Chloride Transport inChara

Abstract

Chara cells show an inward positive electric current across the plasmalemma when exposed to Cl⁻ under voltage-clamp conditions. The rapid rise of this current suggests that it is directly associated with the inward transport of Cl⁻. The dependence of the current on Cl⁻ concentration shows saturation, the data fitting the Michaelis-Menten equation with V_m up to 100 nmol m⁻² s⁻¹ (for Cl⁻starved cells) with K_M 10–20 μM, and with some allowance for an unstirred layer of water adjacent to the membrane. The effects on the current of clamp potential, illumination, withdrawal of alkali metal cations, and addition of amine were also investigated. These results suggest that the mechanism is the symport of 2 H⁺ with each Cl⁻, and that the actions of light, external K⁺, and amine in stimulating Cl⁻, influx are indirect.