Abstract 247: Suppression of 8,9-Epoxyeicosatrienoic Acid (EET), 11,12-EET, and 14,15-EET as a Mechanism for Endothelium-Dependent Coronary Arteriolar Vasoconstriction Induced by Coupling Factor 6
Coupling factor 6 (CF6), a component of ATP synthase, inhibits prostacyclin formation by suppressing the release of arachidonic acid (AA). CF6 therefore appears to decrease the formation of cytochrome P-450-mediated AA metabolites, which are said to mediate hyperpolarization-induced coronary arteriolar dilation. We examined the effect of CF6 on coronary microcirculation and the role of cytochrome P-450 metabolites in it. Coronary arterioles (60–140 μm) were isolated from the heart of spontaneously hypertensive rats (SHR) and control rats (WKY) at the age of 22–24 weeks, and pressurized at 60 mmHg by cannulation. We examined the change in coronary arteriolar diameter in response to CF6 (10−12 M to 10−7 M) with or without NG-nitro-L-arginine methyl ester (L-NAME, 10−4 M) and indomethacin (INDO, 10−5 M). We also examined the effect of endothelial denudation, potassium chloride (KCL, 40 mM), or cytochrome P-450 inhibitor 17-octadecynoic acid (17-ODYA, 10−5 M) on it. We further examined the effects of CF6 (10−9 M) and 17-ODYA on bradykinin (BK, 10−10 to 10−7 M)-induced coronary arteriolar dilatation with L-NAME and INDO. After coronary arterioles were incubated with or without CF6 at 10−7M for 3 hours, released epoxyeicosatrienoic acids (EETs) were measured by HPLC after induction by Br-DMEQ and 18-crown using UV light detector. CF6 produced dose-dependent vasoconstriction in coronary arteriolar diameter in WKY and SHR, and the vasoconstrictor response to CF6 in SHR was significantly greater than that in WKY. Neither L-NAME nor INDO affected the vasoconstrictor effect of CF6, whereas all of KCl, 17-ODYA, and endothelial denudation abolished its vasoconstrictor effect. BK produced dose-dependent increase in coronary arteriolar diameter in both rats, and pretreatment with CF6 or 17-ODYA blocked the dilator response to BK. Coronary arterioles released 14,15-EET>8,9-EET=11,12-EET at baseline, and CF6 at 10−7M suppressed the release of all EETs by 20% and 50% in WKY and SHR, respectively. In conclusion, CF6 induces endothelium-dependent coronary arteriolar vasoconstriction, and this vasoconstrictor response is enhanced in SHR. CF6-induced vasoconstriction is independent of nitric oxide and prostacyclin and is mediated by its suppressing effect on EETs.