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(Circulation. 1999;99:1802-1809.)
© 1999 American Heart Association, Inc.

Clinical Investigation and Reports

Functional Effects of Endothelin and Regulation of Endothelin Receptors in Isolated Human Nonfailing and Failing Myocardium

Presented in part at the 69th Scientific Sessions of the American Heart Association, New Orleans, La, November 10–13, 1996, and published in abstract form (Circulation. 1996;94[suppl I]:I-406).

Burkert Pieske, MD, ; Beate Beyermann, MD, ; Volker Breu, PhD, ; Bernd M. Löffler, MD, ; Klaus Schlotthauer, MD, ; Lars S. Maier, MD, ; Stephan Schmidt-Schweda, MD, ; Hanjörg Just, MD, ; Gerd Hasenfuss, MD,

From the Zentrum Innere Medizin, Abteilung Kardiologie und Pneumologie, Georg-August-Universität, Göttingen, Germany (B.P., B.B., K.S., L.S.M., G.H.); Preclinical Research, Hoffmann–La Roche, Basel, Switzerland (V.B., B.M.L.); and Medizinische Klinik III, Abteilung Kardiologie und Angiologie, Albert-Ludwigs-Universität, Freiburg, Germany (S.S., H.J.).

Correspondence to Priv-Doz Dr Burkert Pieske, MD, Zentrum Innere Medizin, Abteilung Kardiologie und Pneumologie, Georg-August-Universität, Robert-Koch-Str 40, 37075 Göttingen, Germany.

	Abstract

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Background—An activated endothelin (ET) system may be of pathophysiological relevance in human heart failure. We characterized the functional effects of ET-1, ET receptors, and ET-1 peptide concentration in left ventricular myocardium from 10 nonfailing hearts (NF) and 27 hearts in end-stage failure due to idiopathic dilative cardiomyopathy (DCM).

Methods and Results—Inotropic effects were characterized in isolated muscle strips (1 Hz; 37°C). ET-1 0.0001 to 0.3 µmol/L significantly (P<0.05) increased twitch force by maximally 59±10% in NF and by 36±11% in DCM (P<0.05 versus NF). Preincubation with propranolol 1 µmol/L and prazosin 0.1 µmol/L did not affect the response to ET-1, but the mixed ET receptor antagonist bosentan and the ET_A receptor antagonist BQ-123 shifted the concentration-response curves for ET-1 rightward. The ET_B receptor agonist sarafotoxin S6c 0.001 to 0.3 µmol/L had no functional effects. The inotropic response to ET-1 was not associated with increased intracellular Ca²⁺ transients, as assessed in aequorin-loaded muscle strips. ET receptor density (B_max; radioligand binding) was 62.5±12.5 fmol/mg protein in NF and 122.4±24.3 fmol/mg protein in DCM (P<0.05 versus NF). The increase in B_max in DCM resulted from an increase in ET_A receptors without change in ET_B receptors. ET-1 peptide concentration (radioimmunoassay) was higher in DCM than in NF (14 447±2232 versus 4541±1340 pg/mg protein, P<0.05).

Conclusions—ET-1 exerts inotropic effects in human myocardium through ET_A receptor–mediated increases in myofibrillar Ca²⁺ responsiveness. In DCM, functional effects of ET-1 are attenuated, but ET_A receptor density and ET-1 peptide concentration are increased, indicating an activated local cardiac ET system and possibly a reduced postreceptor signaling efficiency.

Key Words: endothelin • cardiomyopathy • contractility • receptors • Ca²⁺ handling

	Introduction

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Endothelin-1 (ET-1) is an endogenous vasoconstrictive peptide that increases blood pressure as well as the plasma concentrations of vasopressin, renin, aldosterone, epinephrine, norepinephrine, and atrial natriuretic peptide.¹ In addition, ET-1 acts as a growth factor inducing hypertrophy.² Furthermore, ET-1 exerts positive inotropic effects in rat,^{3 4} rabbit,^{5 6} and ferret⁷ but not in guinea pig⁸ or dog⁶ myocardium. Recently, a local ET production in the heart has been demonstrated; it is secreted from the endocardium, the myocardium, and the coronary endothelium,^{9 10} thereby acting in a paracrine and autocrine fashion on myocytes.

ET plasma levels are elevated in patients with chronic heart failure,^{11 12} and increased ET-1 levels participate in the maintenance of cardiac contractile function in rats with congestive heart failure.¹³ Endogenous ET-1 contributes to the maintenance of vascular tone in healthy men¹⁴ and to vasoconstriction in severe chronic heart failure.^{15 16} However, a possible functional role of ET-1 in the human heart remains to be elucidated. Despite controversial reports on the effects of ET-1 in mammalian myocardium, little is known about its direct actions in human myocardium. Qiu et al¹⁷ showed a Ca²⁺-sensitizing effect of ET-1 in myocytes from failing human hearts, and Schömisch-Moravec et al¹⁸ demonstrated a slight increase in force in muscle strips from failing hearts. However, both studies investigated only one concentration of ET-1 and made no comparison between nonfailing and failing myocardium. Autoradiographic studies have shown the existence of ET receptors in human atrial and ventricular myocardium but did not address the question of ET receptor regulation in heart failure.^{19 20} Recently, Pönicke et al²¹ demonstrated both ET_A and ET_B receptors in human cardiac tissue by radioligand binding studies. ET-1 peptide has been detected in human myocardium, but no comparison between nonfailing and failing tissue was made.²²

Therefore, the goal of the present study was to characterize the inotropic effects of ET-1, the ET receptor subtype involved in this effect, and the subcellular mechanism of action of ET-1 in isolated myocardium from nonfailing and end-stage failing human hearts. Furthermore, possible alterations of ET receptors and ET-1 peptide concentrations in idiopathic dilative cardiomyopathy (DCM) were characterized.

	Methods

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Myocardial Tissue
Functional experiments were performed in isolated left ventricular muscle strips from 10 nonfailing human hearts that could not be transplanted for technical reasons and 27 end-stage failing hearts (DCM; ejection fraction, 22±1%). For biochemical analyses, transmyocardial specimens of left ventricular tissue (1 to 3 g), free of macroscopic fatty tissue and coronary arteries, were frozen in liquid nitrogen immediately after explantation and stored at -80°C. The study was approved by the Ethical Committee of the University Clinics of Freiburg.

Functional Measurements
Muscle Strip Preparation
Muscle strips were prepared as previously described,²³ mounted in an organ chamber, superfused with modified Krebs-Ringer solution (37°C; pH 7.4), and attached to a force transducer (F30; Hugo Sachs Electronics). The solution contained (in mmol/L) Na⁺ 152, K⁺ 3.6, Cl^- 135, HCO₃^- 25, Mg²⁺ 0.6, H₂PO₄^- 1.3, SO₄^2- 0.6, Ca²⁺ 2.5, and glucose 11.2, and 10 IU/L insulin. The muscle strips were electrically stimulated by field stimulation and gradually stretched until maximum isometric twitch tension (mN/mm² cross-sectional area) was reached. Cross-sectional area was determined as the ratio of blotted muscle weight to length (average for nonfailing, 0.43±0.07 mm² and for DCM, 0.48±0.05 mm², P=NS).

Experimental Protocol
After complete mechanical stabilization, cumulative concentration-response curves for ET-1 0.0001 to 0.3 µmol/L or the specific ET_B receptor agonist sarafotoxin S6c 0.001 to 0.3 µmol/L were established. Additional experiments were performed after muscle strips had been preincubated for 30 minutes with prazosin 0.1 µmol/L, propranolol 1 µmol/L, the mixed ET receptor antagonist bosentan 3 and 30 µmol/L, or the specific ET_A receptor antagonist BQ-123 0.03 and 0.3 µmol/L.

Aequorin Measurements
To assess the effects of ET-1 on intracellular Ca²⁺ transients, muscle strips were loaded with the photoprotein aequorin as described previously.²³ Briefly, aequorin 1 to 3 µL was macroinjected through a fine-tipped glass micropipette into the quiescent muscle. Changes in aequorin light emission, reflecting changes in intracellular Ca²⁺ transients, were detected by a photomultiplier (XP 2802, Philipps). Light emission (mV photomultiplier output) and isometric force (mN) were recorded simultaneously on an oscilloscope with signal-averaging function (Nicolet PRO 10C, Nicolet Instrument Corp) and on a chart recorder (WR 3310, Graphtec). After complete stabilization of aequorin light and force signals, cumulative concentration-response curves for ET-1 0.0001 to 0.3 µmol/L or extracellular Ca²⁺ ([Ca²⁺]_o) 1.25 to 4 mmol/L were performed in nonfailing and end-stage failing myocardium.

Radioligand Binding
Membrane Preparation
Microsomal membrane preparations and radioligand binding studies were performed as described in detail elsewhere.²⁴ Briefly, myocardial tissue was homogenized by use of a Polytron homogenizer PT-K (Brinkman Instruments) for 2 minutes in ice-cold buffer of the following composition (in mmol/L): Tris/HCl 5, MgCl₂ 1, and sucrose 250; pH 6.4. After repeated centrifugation and rehomogenization steps, the resulting microsomal membrane homogenate was suspended in 1 mL incubation buffer (Tris/HCl 75 mmol/L, MnCl₂ 25 mmol/L, sucrose 250 mmol/L, chymostatin 2 mg/L, leupeptin 4 mg/L, bacitracin 40 mg/L, pH 7.4), divided into aliquots, and stored at –80°C.

Competitive Radioligand Binding
Incubation suspensions were prepared by addition of 100 µL of microsomal membrane homogenates (final protein concentration, 200 µg/mL), 50 µL of radioactive ¹²⁵I-labeled ET-1, and 100 µL of the competitive cold ligand ET-1, ET-3, or BQ-123 at increasing concentrations. The concentration of ¹²⁵I-labeled ET-1 was 32 pmol/L, equivalent to 30 000 cpm. For displacement of the iodinated ligand, ET-1 was added in 15 different concentrations, ranging from 10^-13 to 10^-6 mol/L. To assess the relative amount of ET_A and ET_B receptors, displacement experiments were performed with increasing concentrations of ET-3 (showing a relative selectivity for the ET_B receptor) and the selective ET_A receptor antagonist BQ-123. All experiments were performed in triplicate and started by adding the membrane homogenate, followed by 180 minutes of incubation at 25°C. Incubation was terminated by filtration of the suspension through a Whatman GF/C glass filter. Filters were washed, and membrane-bound radioactivity remaining in the filter was measured by scintillation gamma counter. Specific binding was determined by subtracting nonspecific binding, as assessed with ET-1 0.1 µmol/L, from total binding. The individual binding experiments were analyzed for receptor distribution, receptor density (B_max), and ligand affinity (K_D) by use of the LIGAND program.

Endothelin-1 Peptide Expression
ET-1 peptide concentration in tissue homogenates was measured by radioimmunoassay (RIA) as described by Löffler and Maire.²⁵ Frozen tissue samples were thawed on ice and homogenized in a 10-fold wet weight volume of 0.9% NaCl solution and kept at 0°C to 4°C. Aliquots of 100 and 200 µL were mixed with 1 mL methanol. Precipitated protein was sedimented at 3000g for 10 minutes. The methanol/water phase was evaporated to dryness and redissolved in RIA buffer, and ET-1 was determined as described.²⁵ ET extraction efficacy, as measured by spiking of homogenates with ET-1 10 to 100 pg, was determined to be >90%.

Materials
ET-1 (porcine/human; Sigma Chemical Co) was dissolved in deionized water in a concentration of 10 µmol/L and stored at -80°C until use. BQ-123, sarafotoxin S6c, and isoproterenol hydrochloride were also obtained from Sigma. Bosentan was obtained from Hoffmann–La Roche.

Statistical Analysis
Average values are given as mean±SEM. Comparison within one group of myocardium was performed by use of paired t test and Bonferroni-Holms equation. Comparisons between different groups were performed by ANOVA followed by Student-Newman-Keuls test. For analysis of binding data, the average from triplicate experiments under each condition was used. Differences were considered significant at P<0.05.

	Results

Top Abstract Introduction Methods Results Discussion References

 
Positive Inotropic Effects of ET-1 in Isolated Human Myocardium
ET-1 exerted clear positive inotropic effects in human myocardium. Figure 1 shows original recordings from typical experiments. In a nonfailing preparation (top panel), isometric force increased from 6.5 to 11.4 mN. In a preparation from a failing heart (bottom panel), the positive inotropic effect was less pronounced (increase from 4.9 to 6.4 mN). There was no initial depression of tension before the rise in twitch force, as has been previously described in atrial preparations.²⁶

View larger version (13K): [in this window] [in a new window]   Figure 1. Original recordings of positive inotropic effect of a single maximal effective concentration of ET-1 (0.1 µmol/L) in a muscle strip from a nonfailing heart (top) and a DCM heart (bottom).

The concentration-dependent inotropic response to ET-1 is shown in Figure 2. In nonfailing myocardium, the effect started at a concentration of 0.001 µmol/L and was maximal at 0.1 µmol/L ET-1. At that concentration, force had increased by 5.3±1.2 mN/mm², or 52±11% (P<0.05; n=10). In DCM, the effect of ET-1 was likewise maximal at 0.1 µmol/L. However, ET-1 increased force only by 3.0±0.5 mN/mm², or 36±11% (P<0.05 versus baseline; n=14). At concentrations >0.01 µmol/L, the positive inotropic effect was significantly more pronounced in nonfailing than in failing myocardium. Despite the reduced effectiveness of ET-1 in failing myocardium, its potency remained unchanged: the EC₅₀ was 4.28 nmol/L (CI, 1.25 to 14.67 nmol/L) in nonfailing and 3.42 nmol/L (CI, 1.52 to 7.66 nmol/L) in failing myocardium (P=NS). ET-1 prolonged both time to peak and relaxation time in a concentration-dependent manner (Table 1).

View larger version (18K): [in this window] [in a new window]   Figure 2. Concentration-response curves for ET-1 0.0001 to 0.3 µmol/L in human nonfailing (, n=10) and end-stage failing (, n=14) myocardium. Increase in twitch force in mN/mm2; *P<0.05 vs basal value before intervention; #P<0.05 vs corresponding value in DCM.

View this table: [in this window] [in a new window]   Table 1. Influence of ET-1 0.1 µmol/L on Time Parameters of the Isometric Twitch

-Adrenergic receptor blockade with prazosin 0.1 µmol/L and ß-adrenergic receptor blockade with propranolol 1 µmol/L did not affect the inotropic response to ET-1 in end-stage failing myocardium (increase in force by 31.7±9.9%; n=8; P=NS versus data without antagonists, not shown). In contrast, the mixed ET receptor antagonist bosentan 3 and 30 µmol/L shifted the concentration-response curves for ET-1 to the right, and at 30 µmol/L bosentan, the maximal inotropic response to ET-1 was attenuated at the concentrations of ET-1 used (Figure 3, left).

View larger version (17K): [in this window] [in a new window]   Figure 3. Left, Effect of bosentan (Bos) on concentration-response curves for ET-1 in DCM. Experiments without Bos (, n=8) or with 3 µmol/L (, n=7) or 30 µmol/L (, n=6) Bos. EC50 values: 3.01 nmol/L (CI, 1.22 to 6.98 nmol/L) without bosentan and 72.43 nmol/L (CI, 31.44 to 112.36 nmol/L) after 3 µmol/L bosentan. Right, Effect of BQ-123 on concentration-response curves for ET-1 in DCM. Experiments without BQ-123 (, n=8) or with 0.03 µmol/L (, n=8) or 0.3 µmol/L (; n=7) BQ-123. EC50 values: 3.01 nmol/L (CI, 1.22 to 6.98 nmol/L) without BQ-123 and 26.54 nmol/L (CI, 5.22 to 134.87 nmol/L) after 0.03 µmol/L BQ-123.

To test whether the inotropic effect of ET-1 is mediated via ET_A or ET_B receptors, experiments were performed after selective blocking of ET_A receptors with BQ-123. BQ-123 at 0.03 and 0.3 µmol/L shifted the concentration-response curve for ET-1 to the right, and with 0.3 µmol/L BQ-123, the maximal inotropic effect of ET-1 was reduced (Figure 3, right). Furthermore, the selective ET_B receptor agonist sarafotoxin S6c 0.001 to 0.3 µmol/L did not elicit any inotropic effects in nonfailing or failing myocardium (Figure 4), whereas ET-1 at 0.1 µmol/L applied after sarafotoxin S6c increased force to 181±20% and 139±18%, respectively (P<0.05 versus baseline for both groups). These data indicate that the functional effects of ET-1 are mediated exclusively via ET_A receptors.

View larger version (14K): [in this window] [in a new window]   Figure 4. Concentration-response curves for sarafotoxin S6c 0.001 to 0.3 µmol/L in 6 muscles from 3 nonfailing (NF, ) and 7 muscles from 7 DCM () hearts. After S6c, ET-1 0.1 µmol/L was applied. *P<0.05 vs basal value before intervention; #P<0.05 vs NF.

Aequorin Experiments
ET-1 increased twitch force with only slight changes in aequorin light emission. This can be seen from superimposed original tracings in aequorin-loaded muscle strips from a nonfailing (Figure 5, left) and a failing heart (Figure 5, middle). In contrast, a similar increase in twitch force in a muscle strip from a nonfailing heart after [Ca²⁺]_o was raised to 4 mmol/L was associated with a substantial increase in aequorin light emission (Figure 5, right). Figure 6 shows concentration-response curves for ET-1 in aequorin-loaded muscle strips from 5 nonfailing (left) and 7 DCM (right) hearts. In nonfailing myocardium, ET-1 resulted in a pronounced increase in force but only slight increases in aequorin light emission. In DCM, the maximal inotropic effect of ET-1 was smaller, and there were only minor changes in aequorin light emission. In contrast, [Ca²⁺]_o (1.25 to 4 mmol/L; data related to basal values at [Ca²⁺]_o=2.5 mmol/L) concentration-dependently increased twitch force from 69±7% to 154±9% in nonfailing (n=6) and from 60±8% to 153±8% in failing (n=6) myocardium, with parallel increases in aequorin light emission (from 68±8% to 138±18% in nonfailing and from 70±8% to 160±13% in failing myocardium, respectively; P<0.05 versus baseline; data not shown). Time to 50% decline of the aequorin light transient (baseline versus 0.1 µmol/L ET-1) increased from 64±7 to 76±7 ms (P<0.05) in nonfailing and from 91±6 to 98±12 ms in failing myocardium (P=NS). Time to 90% decline increased from 199±11 to 215±12 ms (P=NS) and from 194±16 to 213±22 ms (P=NS), respectively.

View larger version (16K): [in this window] [in a new window]   Figure 5. Influence of ET-1 0.1 µmol/L on aequorin light signals (top) and isometric twitches (bottom) in a muscle strip from a nonfailing (left) and a DCM (middle) heart. For comparison, effect of increasing [Ca2+]o from 2.5 to 4 mmol/L is shown on right in a muscle strip from a nonfailing heart.

View larger version (16K): [in this window] [in a new window]   Figure 6. Concentration-dependent effects of ET-1 0.0001 to 0.3 µmol/L on aequorin light emission () and isometric force () in 6 muscles from 5 nonfailing hearts (left) and 9 muscles from 7 end-stage failing (right) hearts. *P<0.05 vs basal values.

For comparing the subcellular mechanism of action of ET-1 and [Ca²⁺]_o, the relation between the concentration-dependent change in twitch force and aequorin light emission for both interventions is plotted in Figure 7 for nonfailing myocardium (according to Reference 27²⁷ ). It becomes obvious that the increase in force after [Ca²⁺]_o is raised is associated with a proportional increase in aequorin light emission, whereas similar changes in force after ET-1 are associated with only minor increases in aequorin light emission.

View larger version (20K): [in this window] [in a new window]   Figure 7. Relationship between % change in isometric twitch force (ordinate) and aequorin light emission (abscissa) for increasing [Ca2+]o and ET-1 concentrations in nonfailing myocardium. Slope of ET-1 line is steeper than slope of [Ca2+]o line, indicating increased Ca2+ responsiveness of myofilaments with ET-1. *P<0.05 vs basal value at [Ca2+]o 2.5 mmol/L or without ET-1.

Radioligand Binding Studies
ET receptors in human myocardium were characterized by competitive radioligand binding using ¹²⁵I-labeled ET-1 and unlabeled ET-1, which binds with similar affinity to ET_A and ET_B receptors, ET-3 with 100-fold higher affinity for the ET_B receptor, and the selective ET_A receptor antagonist BQ-123. Figure 8 shows average values from displacement experiments for increasing concentrations of ET-1, ET-3, and BQ-123 in left ventricular myocardial membrane preparations from 5 nonfailing and 7 DCM hearts. In DCM, compared with nonfailing myocardium, the remaining ¹²⁵I-labeled ET-1 binding in the presence of BQ-123 is significantly decreased, from 40% to 25%. Accordingly, the upper part of the ET-3 displacement curve is shifted rightward, indicating a low affinity of the ET_B-specific ligand ET-3. LIGAND analysis of the individual experiments revealed both ET_A and ET_B receptors in human cardiac tissue, and the relative proportion of the ET_A receptor increased from 63±5% in nonfailing to 73±3% in failing myocardium (Table 2). This was the result of an increased absolute number of ET_A receptors. ET_A receptor density was 38.1±6.3 fmol/mg protein in nonfailing and 88.3±17.4 fmol/mg protein in DCM hearts (P<0.05 versus nonfailing). ET_B receptor density was lower than ET_A receptor density in both types of myocardium and was not altered in DCM. Total ET receptor density (B_max) was 62.5±12.5 fmol/mg protein in nonfailing myocardium and increased to 122.4±24.3 fmol/mg protein in DCM (P<0.05 versus NF) because of the selective upregulation of ET_A receptors. There were no significant differences in the K_D values for ET-1, ET-3, and BQ-123 between nonfailing and failing myocardium. B_max values and binding characteristics of both ET_A and ET_B receptors are summarized in Table 2.

View larger version (17K): [in this window] [in a new window]   Figure 8. Radioligand binding experiments performed with 125I-labeled ET-1 and increasing concentrations of ET-1, ET-3, and BQ-123 in membrane preparations from 5 nonfailing (left) and 7 DCM (right) hearts. B/B0 percentage indicates bound-to-free ratio.

View this table: [in this window] [in a new window]   Table 2. Characterization of Endothelin Receptors

Endothelin-1 Peptide Tissue Concentration
ET-1 peptide concentration was measured in left ventricular homogenates from 5 nonfailing and 5 end-stage failing hearts. ET-1 peptide concentration in nonfailing myocardium was 4541±1340 pg/mg protein (1.8±0.5 fmol/mg). ET-1 peptide concentration was significantly increased in DCM to 14 447±2232 pg/mg protein (5.8±0.9 fmol/mg; P<0.05 versus nonfailing).

	Discussion

Top Abstract Introduction Methods Results Discussion References

 
The main findings of this study are that (1) ET-1 exerts direct inotropic effects in human ventricle that are reduced in failing compared with nonfailing myocardium, (2) functional responses are mediated via ET_A receptors and are not associated with significant increases in intracellular Ca²⁺ transients, and (3) ET_A receptor density and ET-1 peptide concentration are increased in DCM.

Functional Effects of ET-1
Direct positive inotropic effects of ET-1 have been described in rat, rabbit, and ferret^{3 4 5 6 7} but not in guinea pig⁸ or dog⁶ myocardium. Recently, a direct inotropic effect of ET-1 has been reported for human atrial myocardium,²⁶ and a single concentration of ET-1 showed inotropic responses in muscle strips¹⁸ and isolated myocytes¹⁷ from failing human hearts. Furthermore, ET_A and ET_B receptors were demonstrated in human myocardium, and ET_A receptor mRNA was recently found in human cardiac myocytes.²⁸ However, the exact characterization of the functional effects of ET-1 in nonfailing and failing human ventricles and the ET receptor subtype involved in this effect remained to be determined.

From this study, it is evident that ET-1 exerts a concentration-dependent inotropic response in nonfailing and failing myocardium. This effect is comparable to -adrenergic receptor stimulation but is only 20% to 30% of the maximal inotropic effect that can be obtained with ß-adrenergic receptor stimulation in human cardiac muscle. As assessed by - and ß-adrenergic receptor blockade, the inotropic response to ET-1 is independent of activation of these receptors. In contrast, the mixed ET receptor antagonist bosentan as well as the selective ET_A receptor antagonist BQ-123 shifted the concentration-response curve for ET-1 to the right. In contrast, selective ET_B receptor stimulation with sarafotoxin S6c did not elicit any inotropic response. These data suggest that the inotropic effect of ET-1 is mediated specifically and exclusively via ET_A receptors located on ventricular myocytes. This is in contrast to the rat heart, in which ET_B receptor–mediated inotropic effects of ET-1 have been reported.²⁹

Endothelin Receptor Densities
Elevated ET plasma levels in patients with congestive heart failure^{11 12 15} might influence ET receptor regulation. In contrast to observations in the ß-adrenergic receptor system,³⁰ but similar to -adrenergic receptors,³¹ the present study shows increased cardiac ET receptor densities in DCM without changes in the affinity of the receptors for their ligands. The upregulation of ET receptors was due to a selective upregulation of ET_A receptors with no change in ET_B receptor density.

In animal models of heart failure, both upregulation and downregulation of ET receptors were reported.^{32 33} ET receptor densities in this study in DCM are similar to results from autoradiographic studies by Molenaar et al¹⁹ in 4 failing human hearts. Corresponding to our data, a subtype distribution of 57% ET_A and 43% ET_B was observed.¹⁹ Furthermore, autoradiographic experiments by Bax et al²⁰ in nonfailing human hearts revealed a subtype distribution of 53% ET_A and 47% ET_B receptors, but these data were not compared with failing myocardium.

In agreement with our binding data, Morawietz and Holtz (Department of Physiology, University of Halle, Germany) observed a significant upregulation of ET_A-receptor mRNA in end-stage failing compared with nonfailing human myocardium (personal communication). However, our results seem to be in contrast to receptor binding data by Pönicke et al²¹ in human cardiac tissue. These authors found a total ET receptor density of 113±27 fmol/mg protein in nonfailing myocardium. Using pooled myocardium from end-stage failing hearts due to both idiopathic dilative and ischemic cardiomyopathy, the authors detected an increase in ET receptor density to 147.5±44 fmol/mg protein, which was not significant. Interestingly, in their study, separate analysis of ET receptors according to pathogenesis of cardiac disease revealed a decline of ET receptors in ischemic (81.9±12 fmol/mg protein; n=5) but a 2-fold increase in dilative cardiomyopathy (213±82 fmol/mg protein; n=5). We also found a decline of ET receptor expression in ischemic cardiomyopathy (43.2±5.7 fmol/mg protein; n=6; unpublished data). Therefore, it seems possible that ET receptor expression is differentially regulated in dilative versus ischemic cardiomyopathy, and pooling of myocardium with both diseases might contribute to the lack of significance for the ET receptor increase in the study by Pönicke et al.²¹

Because radioligand binding studies in myocardial homogenates do not allow us to discriminate between receptors on myocytes and on nonmyocytes, the possibility cannot be excluded that upregulation of ET_A receptors on fibroblasts, smooth muscle cells, or endothelium mask a downregulation on cardiac myocytes. However, ET_A receptors are not expressed on human coronary endothelium,³⁴ ET receptor density is lower on fibroblasts than on myocytes,³⁵ and ET receptor number on smooth muscle cells does not exceed ET receptor number on myocytes.³⁶ Therefore, the observed marked upregulation of ET_A receptors in DCM hearts most likely results from increased myocyte receptor density.

ET-1 Tissue Concentration
The existence of a local cardiac ET system has been postulated on the basis of the expression of preproET-1 mRNA³⁷ and peptide,²² but no information about changes in peptide content in human failing myocardium is available. ET-1 exerts its local action in a paracrine and autocrine fashion³⁷ through secretion from endothelial cells toward their abluminal borders³⁸ and direct secretion from cardiac myocytes.¹⁰ We detected a 3-fold increase in ET-1 peptide concentration in DCM, possibly indicating the activation of a local cardiac ET system. However, from our experiments in myocardial homogenates, we cannot localize ET-1 peptide overexpression to either endothelial cells, smooth muscle cells, or cardiac myocytes.

Subcellular Mechanism of Action of ET-1
It was previously reported that ET-1 induces phosphoinositide breakdown,²¹ mediating protein kinase C activation and subsequent stimulation of Na⁺-H⁺ exchange.⁴ This results in intracellular alkalinization and sensitization of the myofilaments for Ca²⁺. Consistently, we did not detect significant increases in intracellular Ca²⁺ after ET-1. Furthermore, we demonstrated that inhibition of protein kinase C or Na⁺/H⁺ exchange prevented the inotropic response to ET-1 but not to isoproterenol in human atrial trabeculae.²⁸

Our findings of an ET-1–induced positive inotropic effect with only minor changes in intracellular Ca²⁺ transients are in agreement with previous reports in animal experiments in ventricular tissue. ET-1 increases contractility but does not change intracellular Ca²⁺ transients in isolated adult ventricular myocytes from rats⁴ and rabbits.³⁹ In contrast, using isolated ferret papillary muscle, Wang and Morgan⁴⁰ demonstrated a slight, albeit significant, increase in [Ca²⁺]_i after ET-1 associated with a 64% increase in twitch force. Furthermore, Qiu et al¹⁷ did not observe an increase in Indo-1 fluorescence associated with increased shortening after ET-1 in human myocytes. For human ventricular myocardium, our results suggest increased myofibrillar Ca²⁺ responsiveness as the major mechanism of action of ET-1. However, we recently found a slight increase in aequorin light emission in human atrial trabeculae,²⁶ but different coupling of endothelin receptors in atrial compared with ventricular myocardium was described.⁴¹ Therefore, we cannot exclude the possibility that small increases in intracellular Ca²⁺, possibly related to increased transsarcolemmal Ca²⁺ influx⁴² or mobilization of Ca²⁺ from intracellular stores⁴³ contributes to the positive inotropic effect of ET-1 in human ventricular tissue.

Possible Mechanisms Underlying the Reduced Functional Effect of ET-1 in DCM
The present finding of a reduced inotropic effect of ET-1 in failing human myocardium is in agreement with a previous report in a rabbit heart failure model.⁴⁴ Downregulation of the ET_A receptor is unlikely to contribute to reduced functional effects of ET-1, because we detected an increased expression and unchanged affinities of the ET_A receptors in DCM. Accordingly, Pönicke et al²¹ found unchanged inositol phosphate accumulation after ET-1 stimulation in failing compared with nonfailing myocardium. However, Freedman et al⁴⁵ recently described a rapid homologous ET_A receptor desensitization by ET-1–induced activation of G protein–coupled receptor kinases and phosphorylation of the receptor. This process may be of importance in the light of increased ET-1 plasma levels in heart failure. Furthermore, the effectiveness of ET-1 to stimulate Na⁺/H⁺ exchange activity was impaired in rat cardiac hypertrophy, resulting in blunted functional effects of ET-1.⁴⁶ This might indicate that alterations in subcellular mechanisms mediating functional responses of ET-1 could contribute to the reduced inotropic effect in diseased myocardium. However, few data regarding such defects were reported for human myocardium. Furthermore, because binding data in myocardial homogenates cannot provide final proof for an upregulation of ET_A receptors on cardiomyocytes, the alterations underlying the reduced effectiveness of ET-1 in DCM deserve further investigation.

Clinical Relevance of the Endothelin System in Heart Failure
The relevance of an activated ET system for maintaining cardiac function has recently been shown for a rat infarct model of heart failure.¹³ However, this may not completely translate into the situation of patients with chronic congestive heart failure, for several reasons: (1) in addition to its positive inotropic effects, ET-1 constricts coronary arteries and peripheral resistance vessels, thereby reducing coronary blood flow and increasing afterload, which might impair contractility^{47 48} ; (2) the inotropic effect of ET-1 is small and accounts for only 20% to 30% of the maximal ß-adrenergic receptor–mediated inotropic effect in nonfailing and failing myocardium; and (3) short-term treatment of patients with severe congestive heart failure with the nonselective ET receptor antagonist bosentan resulted in favorable acute hemodynamic effects,¹⁵ and long-term treatment with bosentan increased survival in a rat model of chronic heart failure.⁴⁹ Therefore, the beneficial effect of ET-1 on contractile performance in the human heart may be offset by increased load, reduced coronary blood flow, and induction of cardiac hypertrophy and remodeling, and treatment of heart failure patients with ET receptor antagonists may be beneficial despite the loss of ET-1–related positive inotropy.

	Footnotes

 
Guest Editor for this article was Richard A. Walsh, MD, University of Cincinnati Medical Center, Cincinnati, Ohio.

Received October 23, 1998; revision received December 4, 1998; accepted December 30, 1998.

	References

Top Abstract Introduction Methods Results Discussion References

 
1. Miller WL, Redfield MM, Burnett JC Jr. Integrated cardiac, renal, and endocrine action of endothelin. J Clin Invest. 1989;83:317–320.

2. Ito H, Hirata Y, Hiroe M, Tsujino M, Adachi S, Takamoto T, Nitta M, Taniguchi K, Marumo F. Endothelin-1 induces hypertrophy with enhanced expression of muscle-specific genes in cultured neonatal rat cardiomyocytes. Circ Res. 1991;69:209–215.[Abstract/Free Full Text]

3. Kelly RA, Eid H, Kramer BK, O'Neill M, Liang BT, Reers M, Smith TW. Endothelin enhances the contractile responsiveness of adult rat ventricular myocytes to calcium by a pertussis toxin-sensitive pathway. J Clin Invest. 1990;86:1164–1171.

4. Krämer BK, Smith TW, Kelly RA. Endothelin and increased contractility in adult rat ventricular myocytes: role of intracellular alkalosis induced by activation of the protein kinase C–dependent Na⁺/H⁺ exchanger. Circ Res. 1991;68:269–279.[Abstract/Free Full Text]

5. Li K, Stewart DJ, Rouleau JL. Myocardial contractile actions of endothelin-1 in rat and rabbit papillary muscles: role of endocardial endothelium. Circ Res. 1991;69:301–312.[Abstract/Free Full Text]

6. Takanashi M, Endoh M. Characterization of positive inotropic effect of endothelin on mammalian ventricular myocardium. Am J Physiol. 1991;261:H611–H619.[Abstract/Free Full Text]

7. Wang JX, Paik G, Morgan JP. Endothelin-1 enhances myofilament Ca²⁺ responsiveness in aequorin-loaded ferret myocardium. Circ Res. 1991;69:582–589.[Abstract/Free Full Text]

8. Volkmann R, Bokvist K, Wennmalm A. Endothelin has no positive inotropic effect in guinea-pig atria or papillary muscle. Acta Physiol Scand. 1990;138:345–348.[Medline] [Order article via Infotrieve]

9. Evans HG, Lewis MJ, Shah AM. Modulation of myocardial relaxation by basal release of endothelin from endocardial endothelium. Cardiovasc Res. 1994;28:1694–1699.[Medline] [Order article via Infotrieve]

10. Suzuki T, Kumazaki T, Mitsui Y. Endothelin-1 is produced and secreted by neonatal rat cardiac myocytes in vitro. Biochem Biophys Res Commun. 1993;191:823–830.[Medline] [Order article via Infotrieve]

11. McMurray JJ, Ray SG, Abdullah I, Dargie HJ, Morton JJ. Plasma endothelin in chronic heart failure. Circulation. 1992;85:1374–1379.[Abstract/Free Full Text]

12. Wei CM, Lerman A, Rodeheffer RJ, McGregor CG, Brandt RR, Wright S, Heublein DM, Kao PC, Edwards WD, Burnett JC Jr. Endothelin in human congestive heart failure. Circulation. 1994;89:1580–1586.[Abstract/Free Full Text]

13. Sakai S, Miyauchi T, Sakurai T, Kasuya Y, Ihara M, Yamaguchi I, Goto K, Sugishita Y. Endogenous endothelin-1 participates in the maintenance of cardiac function in rats with congestive heart failure: marked increase in endothelin-1 production in the failing heart. Circulation. 1996;93:1214–1222.[Abstract/Free Full Text]

14. Haynes WG, Ferro CE, Webb DJ. Physiological role of endothelin in maintenance of vascular tone in humans. J Cardiovasc Pharmacol. 1995;26(suppl 3):183–185.

15. Kiowski W, Sütsch G, Hunziker P, Müller P, Kim J, Oechslin E, Schmitt R, Jones R, Bertel O. Evidence for endothelin-1-mediated vasoconstriction in severe chronic heart failure. Lancet. 1995;346:732–736.[Medline] [Order article via Infotrieve]

16. Webb DJ. Evidence for endothelin-1–mediated vasoconstriction in severe chronic heart failure: endothelin antagonism in heart failure. Circulation. 1995;92:3372.[Free Full Text]

17. Qiu Z, Wang J, Perreault CL, Meuse AJ, Grossman W, Morgan JP. Effects of endothelin on intracellular Ca²⁺ and contractility in single ventricular myocytes from the ferret and human. Eur J Pharmacol. 1992;214:293–296.[Medline] [Order article via Infotrieve]

18. Schömisch-Moravec C, Reynolds E, Stewart R, Bond M. Endothelin is a positive inotropic agent in human and rat heart in vitro. Biochem Biophys Res Commun. 1989;159:14–18.[Medline] [Order article via Infotrieve]

19. Molenaar P, O'Reilly G, Sharkey A, Kuc RE, Harding DP, Plumpton C, Gresham GA, Davenport AP. Characterization and localization of endothelin receptor subtypes in the human atrioventricular conducting system and myocardium. Circ Res. 1993;72:526–538.[Abstract/Free Full Text]

20. Bax WA, Bruinvels AT, van Sylen RJ, Saxena PR, Hoyer D. Endothelin receptors in the human coronary artery, ventricle and atrium: a quantitative autoradiographic analysis. Arch Pharmacol. 1993;348:403–410.

21. Pönicke K, Vogelsang M, Heinroth M, Becker K, Zolk O, Böhm M, Zerkowski HR, Brodde OE. Endothelin receptors in the failing and nonfailing human heart. Circulation. 1998;97:744–751.[Abstract/Free Full Text]

22. Plumpton C, Ashby MJ, Kuc RE, O'Reilly G, Davenport AP. Expression of endothelin peptides and mRNA in the human heart. Clin Sci. 1996;90:37–46.[Medline] [Order article via Infotrieve]

23. Pieske B, Sütterlin M, Schmidt-Schweda S, Minami K, Meyer M, Olschewski M, Holubarsch C, Just H, Hasenfuss G. Diminished post-rest potentiation of contractile force in human dilated cardiomyopathy. J Clin Invest. 1996;98:764–776.[Medline] [Order article via Infotrieve]

24. Fischli W, Clozel M, Guilly C. Specific receptors for endothelin on membranes from human placenta: characterization and use in a binding assay. Life Sci. 1989;44:1429–1436.[Medline] [Order article via Infotrieve]

25. Löffler BM, Maire JP. Radioimmunological determination of endothelin peptides in human plasma: a methodological approach. Endothelium. 1994;1:273–286.

26. Meyer M, Lehnart S, Pieske B, Schlotthauer K, Munk S, Holubarsch C, Just H, Hasenfuss G. Influence of endothelin-1 on human atrial myocardium: myocardial function and subcellular pathways. Basic Res Cardiol. 1996;91:86–93.[Medline] [Order article via Infotrieve]

27. Blinks JR, Endoh M. Modification of myofibrillar responsiveness to Ca²⁺ as an inotropic mechanism. Circulation 1986;73(suppl III):III-85–III-98.

28. Hasegawa K, Fujiwara H, Koshiji M, Inada T, Ohtani S, Doyama K, Tanaka M, Matsumori A, Fujiwara T, Shirakami G, Hosoda K, Nakao K, Sasayama S. Endothelin-1 and its receptor in hypertrophic cardiomyopathy. Hypertension. 1996;27:259–264.[Abstract/Free Full Text]

29. Beyer ME, Nerz S, Kazmaier S, Hoffmeister HM. Effect of endothelin-1 and its combination with adenosine on myocardial contractility and myocardial energy metabolism in vivo. J Mol Cell Cardiol. 1995;27:1989–1997.[Medline] [Order article via Infotrieve]

30. Brodde OE. ß-Adrenoceptors in cardiac disease. Pharmacol Ther. 1993;60:405–430.[Medline] [Order article via Infotrieve]

31. Vago T, Bevilacqua M, Norbiato G, Baldi G, Chebat E, Bertora P, Baroldi G, Accinni R. Identification of ₁-adrenergic receptors on sarcolemma from normal subjects and patients with idiopathic dilated cardiomyopathy: characteristics and linkage to GTP-binding protein. Circ Res. 1989;64:474–481.[Abstract/Free Full Text]

32. Löffler BM, Roux S, Kalina B, Clozel M, Clozel JP. Influence of congestive heart failure on endothelin levels and receptors in rabbits. J Mol Cell Cardiol. 1993;25:407–416.[Medline] [Order article via Infotrieve]

33. Miyauchi T, Sakai S, Ihara M, Kasuya Y, Yamaguchi I, Goto K, Sugishita Y. Increased endothelin-1 binding sites in the cardiac membranes in rats with chronic heart failure. J Cardiovasc Pharmacol. 1995;26(suppl 1):S448–S451.

34. Russell FD, Skepper JN, Davenport AP. Detection of endothelin receptors in human coronary artery vascular smooth muscle cells but not endothelial cells by using electron microscope autoradiography. J Cardiovasc Pharmacol. 1997;29:820–826.[Medline] [Order article via Infotrieve]

35. Fareh J, Touyz RM, Schiffrin E, Thibault G. Endothelin-1 and angiotensin receptors in cells from rat hypertrophied heart: receptor regulation and intracellular Ca²⁺ modulation. Circ Res. 1996;78:302–311.[Abstract/Free Full Text]

36. Dagassan PH, Breu V, Clozel M, Künzli A, Vogt P, Turina M, Kiowski W, Clozel JP. Upregulation of endothelin ET_B receptors in atherosclerotic human coronary arteries. J Cardiovasc Pharmacol. 1996;27:147–153.[Medline] [Order article via Infotrieve]

37. Ito H, Hirata Y, Adachi S, Tanaka M, Tsujino M, Koike A, Nogami A, Murumo F, Hiroe M. Endothelin-1 is an autocrine/paracrine factor in the mechanism of angiotensin II-induced hypertrophy in cultured rat cardiomyocytes. J Clin Invest. 1993;92:398–403.

38. Yoshimoto S, Ishizaki Y, Kurihara H, Sasaki T, Yoshizumi M, Yanagisawa M, Yazaki Y, Masaki T, Takakura K, Murota S. Cerebral microvessel endothelium is producing endothelin. Brain Res. 1990;508:283–285.[Medline] [Order article via Infotrieve]

39. Fujita S, Endoh M. Effects of endothelin-1 on [Ca²⁺]_i-shortening trajectory and Ca²⁺-sensitivity in rabbit single ventricular cardiomyocytes loaded with indo-1/AM: comparison with the effects of phenylephrine and angiotensin II. J Cardiac Failure. 1996;4S:45–57.

40. Wang J, Morgan JP. Endothelin reverses the effects of acidosis on the intracellular Ca²⁺ transients and contractility in ferret myocardium. Circ Res. 1992;71:631–639.[Abstract/Free Full Text]

41. Vogelsang M, Boede-Sitz A, Schäfer E, Zerkowski H-R, Brodde O-E. Endothelin ET_A-receptors couple to inositol phosphate formation and inhibition of adenylate cyclase in human right atrium. J Cardiovasc Pharmacol. 1994;23:344–347.[Medline] [Order article via Infotrieve]

42. Lauer MR, Gunn MD, Clusin WT. Endothelin activates voltage-dependent Ca²⁺ current by a G-protein-dependent mechanism in rabbit cardiac myocytes. J Physiol (Lond). 1992;448:729–747.[Abstract/Free Full Text]

43. Marsden PA, Danthuluri NR, Brenner BM, Ballermann BJ, Brock TA. Endothelin action on vascular smooth muscle involves inositol triphosphate and calcium mobilisation. Biochem Biophys Res Comm. 1989;158:170–176.[Medline] [Order article via Infotrieve]

44. Kelso EJ, Geraghty RF, McDermott BJ, Trimble ER, Nicholls DP, Silke B. Mechanical effects of ET-1 in cardiomyocytes isolated from normal and heart-failed rabbits. Mol Cell Biochem. 1996;157:149–155.[Medline] [Order article via Infotrieve]

45. Freedman NJ, Ament AS, Oppermann M, Stoffel RH, Exum ST, Lefkowitz RJ. Phosphorylation and desensitization of human endothelin A and B receptors. J Biol Chem. 1997;272:17734–17743.[Abstract/Free Full Text]

46. Ito N, Kagaya Y, Weinberg EO, Barry WH, Lorell BH. Endothelin, and angiotensin II stimulation of Na⁺/H⁺ exchange is impaired in cardiac hypertrophy. J Clin Invest. 1997;99:125–135.[Medline] [Order article via Infotrieve]

47. Dagassan PH, Clozel M, Breu V, Clozel JP. Role of endothelin in spontaneous phasic contraction of human coronary arteries. J Cardiovasc Pharmacol. 1995;26(suppl 3):S200–S203.

48. Karwatowska-Prokopczuk E, Wennmalm A. Effects of endothelin on coronary flow, mechanical performance, oxygen uptake, and formation of purines and on outflow of prostacyclin in the isolated rabbit heart. Circ Res. 1990;66:46–54.[Abstract/Free Full Text]

49. Mulder P, Richard V, Derumeaux G, Hogie M, Henry JP, Lallemand F, Compagnon P, Mace B, Comoy E, Letac B, Thuillez C. Role of endogenous endothelin in chronic heart failure: effect of long-term treatment with an endothelin antagonist on survival, hemodynamics, and cardiac remodeling. Circulation. 1997;96:1976–1982.[Abstract/Free Full Text]

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