Role of endothelial cell hyperpolarization in EDHF-mediated responses in the guinea-pig carotid artery

1 Experiments were performed to identify the potassium channels involved in the acetylcholine-induced endothelium-dependent hyperpolarization of the g uinea-pig internal carotid artery. Smooth muscle and endothelial cell membr ane potentials were recorded in isolated arteries with intracellular microe lectrodes. Potassium currents were recorded in freshly-dissociated smooth m uscle cells using patch clamp techniques. 2 In single myocytes, iberiotoxin (0.1 mu M)-, charybdotoxin (0.1 mu M)-, a pamin (0.5 mu M)- and 4-aminopyridine (5 mM)-sensitive potassium currents w ere identified indicating the presence of large- and small-conductance calc ium-sensitive potassium channels (BKCa and SKCa) as well as voltage-depende nt potassium channels (K-V) Charybdotoxin and iberiotoxin inhibited the sam e population of BKCa but a conductance specifically sensitive to the combin ation of charybdotoxin plus apamin could not be detected. 4-aminopyridine ( 0.1-25 mM) induced a concentration-dependent inhibition of K-V without affe cting the iberiotoxin- or the apamin-sensitive currents. 3 In isolated arteries, both the endothelium-dependent hyperpolarization of smooth muscle and the hyperpolarization of endothelial cells induced by ac etylcholine or by substance P were inhibited by 5 mM 4-aminopyridine. 4 These results indicate that in the vascular smooth muscle cells of the gu inea-pig carotid artery, a conductance specifically sensitive to the combin ation of charybdotoxin plus apamin could not be detected, comforting the hy pothesis that the combination of these two toxins should act on the endothe lial cells. Furthermore, the inhibition by 4-aminopyridine of both smooth m uscle and endothelial hyperpolarizations, suggests that in order to observe an endothelium-dependent hyperpolarization of the vascular smooth muscle c ells, the activation of endothelial potassium channels is likely to be requ ired.