A Ca2+- and Voltage-Dependent Cl− -Sensitive Anion Channel in the Chara Plasmalemma: A Patch-Clamp Study

Abstract

The inside-out patch-clamp technique was applied to the plasmolyzed plasmalemma of inter-nodes of Chara corallina without enzymatic treatment. We found two different types of channel activity that were CP−-sensitive. Both types of channel were Ca2+-dependent. However, the one that exhibited greater dependence on Ca2+ ions was the focus of our studies, and we named it the Ca2+-dependent CP−-sensitive anion channel. When the concentration of Ca2+ ions on the cyto-plasmic side was 1.0 μM, the Ca2+-dependent CP−-sensitive channel opened most frequently between approximately −80 and −100 mV. At 10 μM Ca2+, it opened less frequently, and at 0.1 μM Ca2+ it scarcely opened at all. These observations indicate that the anion channel of interest is voltage-dependent over a restricted range of concentrations of Ca2+ ions. The dependence on Ca2+ and voltage of the channel can explain the behavior of the excitable Ca2+-activated Cl− channel in the Chara plasmalemma. The channel activity was blocked by several antagonists of calmodulin.