Endothelium-Derived Metabolites of Cytochrome P450 Produce Relaxation of Coronary Small Arteries by Opening Ca'-Dependent IC Channels (Kc.)

摘要

Previously, we reported that acetylcholine (ACh)-induced relaxation that was resistant to inhibition of nitric oxide synthase (NOS) was mediated by opening of K~+ channels in hamster coronary small arteries (150-250 urn). The present study was designed to determine if this vasodilatory response to ACh was due to release of endothelium-derived metabolites of cytochrome P450 acting via opening of Ca~(2+)-dependent K~+ channels (Kca). Intraluminal diameter was continuously recorded in isolated coronary arteries (150-250 urn) obtained from male Golden Syrian hamsters. All vessels were maintained at a constant intraluminal pressure of 40 nmfflg and pretreated with indomethacin (IO ptM). To assess the role of large (BKca) and small (SKCa) channels in regulating relaxation, coronary arteries were pretreated with a combination of charybdotoxin (CTX, O.luM) and apamin (AP, 0.5muM). Relaxation to Ach (10~(-9)to3xl0~(-5) M) was completely abolished by CTX/AP. In endothelium-denuded coronary arteries, relaxation to ACh was also completely abolished indicating that the Independent relaxation is mediated by release of endothelium-derived relaxing factors. The role of the cP450 pathway in mediating relaxation to ACh was determined with inhibitors of cP450 that act through different mechanisms. Miconazole (20muM), which forms a nitrogenous ligand to the heme iron of P450, proadifen (30 muM), which is converted to a reactive intermediate that sequesters cytochrome in a catalytically inactive complexed state, and 1-aminobenzotriazole (I mM), which causes autocatalytic destruction of cP450, significantly inhibited relaxation to ACh that was resistant to inhibition of NOS. These results indicate that endothelium-derived cP450 metabolites contribute to ACh-induced opening of KCa, channels and vascular relaxation of hamster coronary small arteries.