We examined the effect of ethanol on single potassium channels derived from
plasma membranes of bovine tracheal smooth muscles. The observed potassium
channels had a conductance of 296 +/- 31 pS (mean +/-S.D.) in symmetrical
250 mmol/l KCl solutions, and exhibited a voltage- and Ca2+-dependence simi
lar to BKCa channels. Ethanol at 50, 100 and 200 mM concentrations increase
d the probability of open potassium channels to 112 +/-5, 127 +/-7 and 121
+/- 13% (mean +/-S.E.M.), respectively. It is suggested that increased acti
vity of the BKCa channels by ethanol hyperpolarizes the plasma membrane and
thus may contribute to relaxation of tracheal smooth muscle.