PERMEATION SELECTIVITY BY COMPETITION IN A DELAYED RECTIFIER POTASSIUM CHANNEL

Permeation selectivity was studied in two human potassium channels, Kv 2.1 and Kv1.5, expressed in a mouse cell line. With normal concentrati ons of potassium and sodium, both channels were highly selective for p otassium. On removal of potassium, Kv2.1 displayed a large sodium cond uctance that was inhibited by low concentrations of potassium. The cha nnel showed a competition mechanism of selectivity similar to that of calcium channels. In contrast, Kv1.5 displayed a negligible sodium con ductance on removal of potassium. The observation that structurally si milar potassium channels show different abilities to conduct sodium pr ovides a basis for understanding the structural determinants of potass ium channel selectivity.