Ionic currents across the plasmalemma of chara inflata cells i. osmotic effects of sorbitol on potassium chloride and leak currents
Kourie, J.I.; Findlay, G.P.
Journal of Experimental Botany 41(223): 141-150
ISSN/ISBN: 0022-0957 Accession: 007488316
This paper describes experiments designed to investigate the effects of increases in exteranl 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 in 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.