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© 1990 Oxford University Press

RESEARCH-ARTICLE

Ionic Currents across the Plasmalemma of Chara inflata Cells

II. EFFECTS OF EXTERNAL Na+, Ca2+ AND Cl– ON K+ AND Cl CURRENTS

J. I. KOURIE and G. P. FINDLAY1

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

1 To whom correspondence should be addressed.

The electrical conductance of the plasmalemma of cells of Chara inflata, due to the diffusion of ions, consists predominantly of K+, Cl– and leak components. When the membrane electrical potential difference is stepped in a negative direction with a voltage-clamp, the resulting inward current has components IK, ICl and IL (leak). During such voltage-clamp steps IK is inactivated, and Ic activated with voltage-dependent half-times. Increases in the external NaCl concentration reduce the magnitude of IK and increase the magnitude of Ic, but reduce the half-time of inactivation or activation. The NaCl-induced changes in Ik and ICl and their kinetics were more pronounced at pH0 =6.5 than at pH0 =9.5. When the concentration of external CaCl2 was increased, Ik, ICl and the half-time of inactivation, (T1/2), of Ik were all reduced. The half-time of activation of ICl was increased.

The NaCI-induced changes could result from increases in both external ion concentration and osmotic pressure. Previous experiments have shown that an increase in external osmotic pressure alone alters the properties of the conductances. In this paper we attempt to separate the purely ionic effects from the osmotic ones.

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


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