EPOXYEICOSATRIENOIC ACIDS, POTASSIUM CHANNEL BLOCKERS AND ENDOTHELIUM-DEPENDENT HYPERPOLARIZATION IN THE GUINEA-PIG CAROTID-ARTERY

1 Using intracellular microelectrodes, we investigated the effects of 17-octadecynoic acid (17-ODYA) on the endothelium-dependent hyperpolar ization induced by acetylcholine in the guinea-pig isolated internal c arotid artery with endothelium. 2 In the presence of N-omega-nitro-L-a rginine (L-NOARG. 100 mu M) and indomethacin (5 mu M) to inhibit nitri c oxide synthase and cyclo-oxygenase, acetylcholine (1 mu M) evoked an endothelium-dependent hyperpolarization which averaged -16.4 mV start ing from a resting membrane potential of -56.8 mV. There was a negativ e correlation between the amplitude of the hyperpolarization and the a bsolute values of the resting membrane potential. 3 The acetylcholine- induced endothelium-dependent hvperpolarization was not altered by cha rybdotoxin (0.1 mu M) or iberiotoxin (30 nM). It was partially but sig nificantly reduced by apamin (0.5 mu M) to -12.8+/-1.2 mV (n=10) or th e combination of apamin plus iberiotoxin (-14.3+/-3.4 mV, n=4). Howeve r, the combination of charybdotoxin and apamin abolished the hyperpola rization and under these conditions. acetylcholine evoked a depolariza tion (+ 7.1 +/- 3.7 mV, n = 8). 4 17-ODYA (10 mu M) produced a signifi cant hyperpolarization of the resting membrane potential which average d -59.6 mV and a partial but significant inhibition of the acetylcholi ne-induced endothelium-dependent hyperpolarization (-10.9 mV). 5 Apami n did not modify the effects of 17-ODYA but in the presence of charybd otoxin or iberiotoxin, 17-ODYA no longer influenced the resting membra ne potential or the acetylcholine-induced hyperpolarization. 6 When co mpared to solvent (ethanol, 1% v/v), epoxyeicosatrienoic acids (EpETrE s) (5,6-, 8,9-, 11,12- and 14,15-EpETrE, 3 mu M) did not affect the ce ll membrane potential and did not relax the guinea-pig isolated intern al carotid artery. 7 These results indicate that, in the guinea-pig in ternal carotid artery, the involvement of metabolites of arachidonic a cid through the cytochrome P-450 pathway in endothelium-dependent hype rpolarization is unlikely. Furthermore, the hyperpolarization mediated by the endothelium-derived hyperpolarizing factor (EDHF) is probably not due to the opening of BKCa channels.