Effect of 4-aminopyridine on potassium permeability of canine tracheal smooth muscle cell membrane.

Effect of 4-aminopyridine (4-AP) on the potassium permeability of the cell membrane of canine tracheal smooth muscle was investigated using 86Rb-efflux. The 86Rb-efflux from the strip was remarkably increased by 20 mM 4-AP in normal physiological solution in the presence of 1 microM atropine. In high potassium and chloride deficient solution, 4-AP (0.3-20 mM) decreased the rate of 86Rb-efflux in a dose-dependent manner. This finding indicates that 4-AP interacted with a single class of site of action in depolarized tracheal smooth muscle. The maximum decrease in 86Rb-efflux and the inhibitory dissociation constant of 4-AP were 42.3% and 1.49 mM, respectively. 4-AP had an inhibitory effect on the K permeability of the cell membrane of canine tracheal smooth muscle, and it seemed to interact with the same site of action of tetraethylammonium (TEA), but was less effective than TEA.