HUMAN CORONARY ARTERIOLAR DILATION TO ARACHIDONIC-ACID DEPENDS ON CYTOCHROME-P-450 MONOOXYGENASE AND CA2-ACTIVATED K+ CHANNELS()

Endothelium-dependent hyperpolarization of vascular smooth muscle cell s (VSMCs) plays a crucial role in regulating vascular tone, especially in resistance vessels. It has been proposed that metabolites of arach idonic acid (AA), formed by cytochrome P-450 monooxygenase (P450), are endothelium-derived hyperpolarizing factors (EDHFs). These metabolite s have been reported to mediate dilation to endogenous vasoactive comp ounds, such as bradykinin and acetylcholine. However, it is not known whether these metabolites of AA contribute to dilation of human resist ance vessels. This is important since it has been proposed that EDHF s erves as a compensatory mechanism to maintain dilation in disease stat es. Therefore, we studied the effect of AA on vessel diameter and VSMC membrane potential in isolated human coronary microvessels. Arteriole s (81+/-5 mu m, n=70) were dissected from right atrial appendages at t he time of cardiac surgery and cannulated at a distending pressure of 60 mmHg and zero flow. Changes in internal diameter were recorded with videomicroscopy. Some vessels were impaled with glass microelectrodes to measure membrane potential of VSMCs while internal diameters were simultaneously recorded. After constriction (47+/-2%) with endothelin- 1, AA (10(-10) to 10(-5) mol/L) induced substantial dilation of human coronary microvessels, which was abolished by removal of the endotheli um. Treatment with 17-octadecynoic acid (17-ODYA, 10(-5) mol/L; a P450 inhibitor) attenuated maximal dilation to AA (49+/-9% versus 91+/-4% [control]; P<0.05 versus control), whereas indomethacin (INDO, 10(-5) mol/L; a cyclooxygenase inhibitor) and N-omega-nitro-L-arginine methyl ester (L-NAME, 10(-4) mol/L; a NO synthase inhibitor) were without ef fect. Both I7-ODYA and miconazole (10(-5) mol/L, a chemically distinct P450 inhibitor) further reduced the dilation to AA in the presence of INDO. The presence of 40 mmol/L KCl or charybdotoxin (10(-8) mol/L, a blocker of large-conductance Ca2+-activated K+ channels) impaired dil ation to AA (19+/-9% [KCl] versus 76+/-5% [control] and 47+/-6% [chary bdotoxin] versus 91+/-3% [control]; P<0.05 for both). After depolariza tion with endothelin-1 (-26+/-1 mV from -48+/-3 mV [before endothelin] ), AA (10-5 mol/L) in the presence of INDO and L-NAME induced hyperpol arization of VSMCs (-57+/-5 mV). In the presence of 17-ODYA together w ith INDO and L-NAME, endothelin produced similar depolarization (-26+/ -2 mV from -48+/-3 mV), but hyperpolarization to AA was reduced (-33+/ -2 mV; P<0.05 versus absence of 17-ODYA). AA metabolites formed primar ily by P450 produce potent endothelium-dependent dilation of human cor onary arterioles via opening of Ca2+-activated K+ channels and hyperpo larization of VSMCs. These findings support an important role for P450 metabolites in the regulation of human coronary arteriolar tone.