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© 1990 Oxford University Press

RESEARCH-ARTICLE

Ionic Currents across the Plasmalemma of Chara inflata Cells

I. OSMOTIC EFFECTS OF SORBITOL ON K+, CI- AND LEAK CURRENTS

J. I. KOURIE and G. P. FINDLAY1

School of Biological Sciences, The Flinders University of South Australia Bedford Park, SA. 5042, Australia

1 To whom correspondence should be addressed.

This paper describes experiments designed to investigate the effects of increases in external osmotic pressure on the electrophysiological behaviour of the plasmalemma in cells of the brackish-water alga, Chara inflata. The electrical conductance of the plasmalemma of these cells of, due to the diffusion of ions, consists mainly of K+, Cl– and leak components. The addition of sorbitol at concentrations in the range 40–280 mol m–3 to the external solution bathing the cells, progressively and reversibly depolarized the cell membrane and increased the total membrane conductance, chiefly due to increases in each of the separate ionic conductances. At concentrations higher than about 280 mol m–3 when the cells became plasmolysed, the effects of sorbitol on the electrical properties of the cell ceased to be fully reversible. When the membrane electrical potential difference is stepped in a negative direction with a voltage-clamp, the resulting inward current has voltage-dependent components consisting of an inactivating K+ current, an activating Cl– current and a constant leak current. The addition of sorbitol to the external solution modified these currents by increasing their magnitude, by increasing the half-time of the inactivation of the K+ current, and by decreasing the half-time of activation of the Cl– current.

Key words: Chara inflata, osmotic effects, K+ and Cl– currents


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