Calcium-activated potassium current in single Novikoff cell

The electrophysiological properties of the hemichannels of the gap junction in a single Novikoff cell was studied using patch-clamp whole-cell recording techniques. During the experiments, a transient outward current (peak current, Ip) was found to be evoked by the increment of depolarized pulses. Ip was voltage-dependent and could be inhibited partly by CsCl and tetraethylammonium (TEA), but was blocked completely by quinidine. When the intracellular free Ca2+ concentration ([Ca2+]i) was increased, the amplitude of Ip was enhanced. Adding 10 mmol/l EGTA in the pipette solution, Ip disappeared. When the cells were bathed in symmetrical high-K+ solution, Ip also completely disappeared. These results suggest that Ip is a calcium-activated potassium current, although it cannot be blocked by apamin.