Chloride Transport in Chara: I. KINETICS AND CURRENT-VOLTAGE CURVES FOR A PROBABLE PROTON SYMPORT

Chara cells show an inward positive electric current acrossthe plasmalemma when exposed to Cl^– under voltage-clampconditions. The rapid rise of this current suggests that itis directly associated with the inward transport of Cl^–.The dependence of the current on Cl^– concentration showssaturation, the data fitting the Michaelis-Menten equation withV_m up to 100 nmol m^–2 s^–1 (for Cl^–starvedcells) with K_M 10–20 µM, and with some allowancefor an unstirred layer of water adjacent to the membrane. Theeffects on the current of clamp potential, illumination, withdrawalof alkali metal cations, and addition of amine were also investigated.These results suggest that the mechanism is the symport of 2H⁺ with each Cl^–, and that the actions of light, externalK⁺, and amine in stimulating Cl^–, influx are indirect.