Potassium conductivity of the plasma membrane of frog photoreceptor cells

Potassium channels, uniformly distributed over the cell surface (0.5 channel/micron2) have been found in isolated fragments of plasma membranes of frog photoreceptor cells. Their conductance under symmetrical conditions (0.1 M KCl at both the membrane surfaces) is 72 +/- 6 pS for rods and 88 +/- 8 pS for cones. The channels are reversibly blocked by tetraethylammonium (TEA), Cs+, Rb+ at intra- and extracellular membrane surfaces. Half-inactivation of a channel occurs at concentrations of TEA, Cs+ and Rb+ at the intracellular surface 0.12, 2.2 and 3.9 mM, correspondingly.