Endothelium-derived factors and hyperpolarization of the carotid artery of the guinea-pig

1 Transmembrane potentials were recorded from isolated carotid arteries of the guinea-pig superfused with modified Krebs-Ringer bicarbonate solution. Smooth muscle cells were impaled from the adventitial side with intracellular glass microelectrodes filled with KCl (30-80 M Omega). 2 Acetylcholine (1 mu M) in the presence of inhibitors of nitric oxide synthase, (N-omega-nitro-L-arginine (L-NOARG) 100 mu M) and cyclo-oxygenase, (indomethacin 5 mu M) induced an endothelium-dependent hyperpolarization (-18.9+/-1.6 mV, n=15). 3 In the presence of these two inhibitors, 3-nitroso-L-glutathione (10 mu M), sodium nitroprusside (10 mu M), 3-morpholinosydnonimine (SIN-1, 10 mu M) and iloprost (0.1 mu M) induced endothelium-independent hyperpolarizations of the smooth muscle cells (respectively: -16.0+/-2.3, -16.3+/-3.4, -12.8+/-2.0 and -14.5+/-1.5 mV, n=4-6). 4 The addition of glibenciamide (1 mu M) did not influence the acetylcholine-induced L-NOARG/indomethacin-resistant hyperpolarization (-18.0+/-1.8 mV, n=10). In contrast, the responses induced by S-nitroso-L-glutathione, sodium nitroprusside, SIN-1 and iloprost were abolished (changes in membrane potential: -0.8+/-1.1, 1.3+/-3.9, 4.5+/-4.6 and 0.3+/-0.8 mV respectively, n=4-5). 5 In the presence of NO synthase and cyclo-oxygenase inhibitors, charybdotoxin (0.1 mu M) or apamin (0.5 mu M) did not influence the hyperpolarization produced by acetylcholine. However, in the presence of the combination of charybdotoxin and apamin, the acetylcholine-induced L-NOARG/indomethacinresistant hyperpolarization was converted to a depolarization (4.4+/-1.2 mV, n=20) while the endothelium-independent hyperpolarizations induced by S-nitroso-L-glutathione, sodium nitroprusside, SIN-1 and iloprost were not affected significantly (respectively: -20.4+/-3.4, -22.5+/-4.9, -14.5+/-4.7 and -14.5+/-0.5 mV, n=4-5). 6 In the presence of the combination of charybdotoxin and apamin and in the absence of L-NOARG and indomethacin, acetylcholine induced a hyperpolarization (-19.5+/-3.7 mV, n=4). This hyperpolarization induced by acetylcholine was not affected by the addition of indomethacin (-18.3+/-4.6 mV, n=3). In the presence of the combination of charybdotoxin, apamin and L-NOARG (in the absence of indomethacin), acetylcholine, in 5 out of 7 vessels, still produced hyperpolarization which was not significantly smaller (-9.1+/-5.6 mV, n=7) than the one observed in the absence of L-NOARG. 7 These findings suggest that, in the guinea-pig isolated carotid artery, the endothelium-independent hyperpolarizations induced by NO donors and iloprost involve the opening of K-ATP channels while the acetylcholine-induced endothelium-dependent hyperpolarization (resistant to the inhibition of NO-synthase and cyclo-oxygenase) involves the opening of Ca2+-activated potassium channel(s). Furthermore, in this tissue, acetylcholine induces the simultaneous release of various factors from endothelial origin: hyperpolarizing factors (NO, endothelium derived hyperpolarizing factor (EDHF) and prostaglandins) and possibly a depolarizing factor.