Ionic Currents across the Plasmalemma ofChara inflataCells

Abstract

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 I_K, I_Cl and I_L (leak). During such voltage-clamp steps I_K is inactivated, and Ic activated with voltage-dependent half-times. Increases in the external NaCl concentration reduce the magnitude of I_K and increase the magnitude of I_c, but reduce the half-time of inactivation or activation. The NaCl-induced changes in I_k and I_Cl and their kinetics were more pronounced at pH₀ =6.5 than at pH₀ =9.5. When the concentration of external CaCl₂ was increased, I_k, I_Cl and the half-time of inactivation, (T_1/2), of I_k were all reduced. The half-time of activation of I_Cl 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.