K+ Channel in the Chora Plasmalemma: Estimations of K+ Channel Density and Single K+ Channel Conductance

The electromotive force E and the conductance G of the Characorallina plasmalemma were measured under voltage clamp conditions.In the depolarized voltage range less negative than –60mV, E changed according to the Nerhst equation for K⁺, and Gincreased with the external K⁺ concentration [K⁺]_o and alsowith the depolarization of the membrane potential. This is attributedto the voltage-dependent opening of the K⁺ channels in the largelydepolarized voltage region. The voltage-dependent increase ofG was due to the increase of the number of open K⁺ channelsper unit area. The density of the total K⁺ channels in the C. corallina plasmalemmawas estimated to be about 6.50/(10 µm)2. The single K⁺channel conductance _K changed with the external [K⁺]_o; it was79.3, 86.1, 105.9, 119.0 pS for external [K⁺]_o of 0.2, 0.5,2.0 and 5.0 mu respectively. (Received May 22, 1986; Accepted August 22, 1986)