[Predominant blocking of fast potassium current channels in mollusk neurons by 4-aminopyridine]

Blocking effects of 4-aminopyridine (4-AP) on ionic currents were studied in Lymnaea stagnalies neurones using the suction pipette method for voltage clamp and internal perfusion. When applied externally, 4-AP blocks transient potassium current as well as early inward and delayed outward currents, apparent dissociation constants being 0.4 mM (E = -40-- -30 mV); 6.5 mM (E = -10-- -20 mV); 24 mM (E = 20 mV), resp. Intracellular 4-AP changes the constants to 0.85, 77, 55 mM. An experimental study of a possible role of the transient potassium channels in the regulation of molluscan unit activity seems to be effective when 4-AP is applied internally as it blocks then the transient potassium channels in a selective manner.