K<sup>+</sup> Channel in the <italic>Chora</italic> Plasmalemma: Estimations of K<sup>+</sup> Channel Density and Single K<sup>+</sup> Channel Conductance

Abstract

The electromotive force E and the conductance G of the Chara corallina plasmalemma were measured under voltage clamp conditions. In the depolarized voltage range less negative than −60 mV, E changed according to the Nerhst equation for K+, and G increased with the external K+ concentration [K+]o and also with the depolarization of the membrane potential. This is attributed to the voltage-dependent opening of the K+ channels in the largely depolarized voltage region. The voltage-dependent increase of G was due to the increase of the number of open K+ channels per unit area. The density of the total K+ channels in the C. corallina plasmalemma was estimated to be about 6.50/(10 μm)2. The single K+ channel conductance γK changed with the external [K+]o; it was 79.3, 86.1, 105.9, 119.0 pS for external [K+]o of 0.2, 0.5, 2.0 and 5.0 mu respectively.