Ionic relations of cells of Chara australis I

Summary The effect of divalent cations and of high chloride ion concentration on voltage-clamp currents in the plasmalemma of O. australis was investigated. Either calcium or strontium ions were necessary in the medium for a transient current to appear during a voltage clamp_ The transient current with strontium was about 20% of that with calcium present. Barium. cadmium, magnesium, manganous, or nickelous ions were unable to replace calcium in. this function. In media containing a chloride concentration of 30 InN, the transient current reversed in sign if the membrane was clamped at potentials more positive than about -50mV. An analysis of the peak transient current as a function of membrane potential was made with the assumptions that a negative transient current corresponded to (a) an inward current of calcium ions, or (b) an outward current of chloride ions. The observations were fairly well fitted by the theory involving chloride ion current if it was assumed that the peak permeability to chloride was of the order of lO~4 cm sec-1 and that the chloride activity in the cytoplasm was 1-10 ruN. It was concluded that calcium ions mediate an increase in the permeability of the plasmalemma not to chloride specifically but to anions such as 01-, Br-, and NO;, following a suitable stimulus. The same peak anion permeabilities were reached and the time courses of the permeability changes were similar during action potentials and during voltage clamps.