| Research Abstract |
Control of vascular tone by endothelium-derived relaxing (EDRF) and hyperpolarizing factors (EDHF) was studied in cultured porcine coronary artery smooth muscle cells and endothelial cells using patch clamp techniques. We characterized two major K channels in smooth muscle cells, i.e.ATP sensitive K channel (KATP) and Ca^<2+>-activated K channels (Kca) and studied the target channels for EDRF and EDHF.These channels were targets organs of various vasoactive substances as well, and many vasoactive aubstances exert their actions through thses channels.
In cell-attached patches, EDRF,which is known as nitric oxide (NO), activated Kca channel of smooth muscle cells via production of cGMP.We also found that NO also activated KATP channels and hyperpolarized membrane. In inside-out patches NO did not activated thses channels. We also studied the effect of EDHF on the ionic channles of smooth muslce cells, where is located close to the coronary artery strips with intact endothelium. In the pre
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sence of N^G-monomethyl L-arginine (LNMMA) and indomethacine, acetylcholine activated Kca channels of smooth muscle, suggesting that the target of EDHF was Kca channels. Tetraethylammonium and charybdotoxin, specific Kca channel blockers, suppressed this channels but glibenclamide, a specific KATP channel blocker, did not significantly altered the channel activity.
We also found new pathway for production of NO from endothelium of porcine coronary artery and aorta. Different from previous studies, histamine did not increased cytosolic Ca^<2+> in endothelium but increased cAMP in endothelium. Histamine produced NO in the presence of histamine H_1 receptor antagonist, but NO production was significantly suppressed in the presence of H_2 receptor antagonist, suggesting that the histamine-induced NO production was mediated by H_2 receptor and through cAMP production. Amrinone, a phosphodiesterase inhibitor, and folskoline, an activator of adenylate cyclase, produced NO from porcine endothelium. These results indicated that there in a new pathway of NO production and that NO is produced by increasing cAMP without increase in cytosolic Ca^<2+>. Less
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