Mechanism Underlying Endothelium-Dependent Relaxation by 2-Methylthio-ADP in Monkey Cerebral Artery

We recently reported endothelium-dependent relaxation caused by nucleotides in the non-human primate cerebral artery. Here, we investigated the endothelium-dependent, nitric oxide- and prostanoid-independent relaxation induced by 2-methylthio-ADP (2MeSADP) in monkey cerebral artery. Mechanical responses of isolated monkey cerebral arteries to the agents were isometrically recorded. In endothelium-intact arterial strips treated with indomethacin plus NG-nitro-l-arginine and partially contracted with prostaglandin F2α, 2MeSADP (1 nM – 10 μM) induced concentration-dependent relaxation that was abolished by removal of endothelium but was not influenced by either carboxy PTIO or 18α-glycyrrhetinic acid. The 2MeSADP-induced relaxation was inhibited by MRS2179 and U73122. The relaxation was markedly suppressed by exposure of the strips to high K+ media, but was not affected by glibenclamide. Combination of charybdotoxin plus apamin markedly suppressed the relaxation, whereas iberiotoxin partially attenuated it. Relaxation induced by 2MeSADP was inhibited by arachidonyl trifluoromethyl ketone, ketoconazole, and 14,15-epoxyeicosa-5(Z)-enoic acid. The inhibitors that affected the 2MeSADP-induced relaxation did not influence relaxation caused by sodium nitroprusside or forskolin. These findings indicate that 2MeSADP elicits ‘endothelium-derived hyperpolarizing factor (EDHF)-type’ relaxation via stimulation of endothelial P2Y1 receptors in monkey cerebral artery. Furthermore, phospholipase A2, cytochrome P450–derived epoxyeicosatrienoic acids and Ca2+-activated K+ channels appear to be involved in the relaxation. Keywords:: Ca2+-activated K+ channel, endothelium-dependent relaxation, epoxyeicosatrienoic acid, monkey cerebral artery, P2Y1 receptor