Abstract 10649: Upregulation and Adverse Effects of Cardiac Beta3-Adrenoreceptor-Mediated Inducible Nitric Oxide Synthase (iNOS)-Coupled Pathway in Monkeys with Naturally Occurring Type 2 Diabetes
Background. Recent evidence links altered cardiac β-adrenergic receptor (AR) signaling to the pathology of diabetic cardiomyopathy (DCM). Although the β3-AR-mediated inhibitory pathway is increasingly emerging as a major player in controlling normal and pathological cardiac function, its role in diabetes mellitus (DM) is unknown. We hypothesized that DM causes coordinated upregulation of myocyte β3-AR and iNOS, enhancing negative modulations of myocyte function, [Ca2+]i regulation, and β-AR signaling effectiveness, thus playing a critical role in DCM.
Methods. Myocytes were isolated from left ventricular (LV) tissues collected terminally from 8 male cynomolgus monkeys: 4 normal and 4 with naturally occurring Type 2 DM, all with no apparent cardiovascular disease. We compared iNOS and β3-AR protein expression and myocyte contractile and [Ca2+]i transient ([Ca2+]iT) responses to β- and β3-AR stimulation with isoproterenol (ISO,10-8M) and BRL-37344 (BRL,10-8 M), respectively, in the absence and presence of a selective iNOS inhibitor, 1400W (10-5 M).
Results. DM myocytes had significantly increased protein levels of iNOS (0.52 vs 0.26) and β3-AR (0.58 vs 0.27) compared to normal myocytes. These changes were associated with reduced basal cell contraction (dL/dtmax) (69.4 vs 120.8 μm/s), relaxation (dR/dtmax) (-60.8 vs -110.9 μm/s), and [Ca2+]iT (0.16 vs 0.29) with diminished β-AR-stimulated positive inotropic response, but enhanced β3-AR-induced negative inotropic response. In DM myocytes, ISO caused much less increase in dL/dtmax (DM: 31.8% vs N: 74.4%) and [Ca2+]iT (14.7% vs 32.9%), but BRL produced a significantly greater decrease in dL/dtmax (-29.5% vs -13.2%) and [Ca2+]iT (-26.4% vs -11.2%). Moreover, only in DM myocytes, pretreatment with 1400W markedly improved basal (163.9 μm/s) and augmented ISO-stimulated increases in dL/dtmax (61.8%) and [Ca2+]iT (28.9%), but significantly limited BRL-induced decrease in dL/dtmax (-14.6%) and [Ca2+]iT (-11.5%).
Conclusions. Type 2 DM is associated with increased stimulation of β3-AR-mediated iNOS-coupled pathway, depressing contractility reserve, exacerbating dysfunctional [Ca2+]i regulation and β-adrenergic modulation, thus apparently preceding the development of DCM.
- Nitric oxide synthase
- Receptor-mediated signaling
- Beta-adrenergic receptor agonists
- Type 2 Diabetes
- © 2011 by American Heart Association, Inc.