Inhibition of Cl<sup>−</sup> Channel Activation in <italic>Chara corallina</italic> Membrane by Lanthanum Ion

Abstract

We examined a role of Ca2+ in the activation of the two major ion channels, i.e., Cl− and K+ channels at the excitation of the characean plasmalemma. The current-voltage relation (I-V curve) of the Chara membrane was compared under the ramp voltage clamp condition before and after external application of 20μM of La3+ (a Ca2+ channel blocker). The transient inward current component, which is carried mainly by the efflux of Cl−, disappeared almost completely in about 30 min with La3+ treatment. On the other hand, no effect was observed on the late large outward current, which is mainly carried by the efflux of K+ in a large depolarization region (less negative than −50 mV). These results suggest that the Cl− channel in the Chara plasmalemma is activated by Ca2+ influx, while the K+ channel is simply activated by depolarization.