Inhibition of Cl^- Channel Activation in Chara corallina Membrane by Lanthanum Ion

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We examined a role of Ca^<2+> 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 20 μM of La^<3+> (a Ca^<2+> channel blocker). The transient inward current component, which is carried mainly by the efflux of Cl^-, disappeared almost completely in about 30 min with La^<3+> 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 Ca^<2+> influx, while the K^+ channel is simply activated by depolarization.
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