Ion channels in the membrane ofChara inflata

Summary Voltage-clamped steps in the electric potential difference (PD) across the membrane in cells of the green alga,Chara inflata, cause voltage- and time-dependent current flows, interpreted to arise from opening and closing of various types of ion channel in the membrane. With cells in the light, these channels are normally closed, and the resting PD is probably determined by the operation of an H⁺ efflux pump. Positive steps in PD from the resting level often caused the opening of K⁺ channels with sigmoid kinetics. The channels began to show opening when the PD–120 mV for an external concentration of K⁺ of 1.0mm. Return of the PD to the resting level caused closing of the channels with complex kinetics. Various treatments of the cell could cause these K⁺ channels to open, and remain open continuously, with the PD then lying closer to the Nernst PD for K⁺. The K⁺ channels have been identified by the blocking effects of TEA⁺. Another group of channels, probably Cl^– and Ca²⁺ associated with the action potential open when the PD is stepped to values less negative than –50 mV. Negative steps from the resting PD cause the slow opening, with a time course of seconds, of yet another type of channel, probably Cl^–.