CHARACTERIZATION OF ACETYLCHOLINE-INDUCED MEMBRANE HYPERPOLARIZATION IN ENDOTHELIAL-CELLS

The characteristics of the hyperpolarization response to acetylcholine (ACh) in endothelial cells from the guinea pig coronary artery were studied by microelectrode recording technique. ACh (30 nM to 3-mu-M) induced membrane hyperpolarization in a dose-dependent manner. The sustenance of the response required the presence of external calcium. The hyperpolarization was not affected by nifedipine (1-mu-M) but was inhibited by the potassium channel blockers charybdotoxin (10 nM), tetraethylammonium (1 mM), and 4-aminopyridine (0.5 mM). Glibenclamide (10-mu-M) and apamin (1-mu-M) were not effective. The inhibitors of endothelium-derived relaxing factor/nitric oxide synthesis N(omega)-nitro L-arginine (50-mu-M) and N(G)-monomethyl L-arginine (30-mu-M) had no effect on the resting membrane potential or the ACh-induced responses. No hyperpolarization was observed with application of sodium nitroprusside (10-mu-M) or 8-bromo-cGMP (0.1-mu-M). Ouabain (10-mu-M) depolarized the membrane significantly by 5 mV, but the ACh hyperpolarization was not affected. Indomethacin (10-mu-M) was without effect on the resting membrane potential or the hyperpolarization to ACh. These results show that ACh-induced hyperpolarization is dependent on external calcium and can be inhibited by certain potassium channel blockers. The hyperpolarization response is not mediated by endothelium-derived relaxing factor/nitric oxide, cGMP, a cyclooxygenase product, or stimulation of the Na-K pump.