Ionic currents across the plasmalemma of Chara inflata cells. II. Effects of external Na+, Ca2+ and Cl- and K+ and Cl- currents

Kourie, J.; Findlay, G.

Journal of experimental botany 41(223): 151-163


ISSN/ISBN: 0022-0957
Accession: 013147209

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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 IL (leak). During such voltage-clamp steps I(K) is inactivated, and I(Cl) activated with voltage-dependent half-times. Increases in the external NaCl concentration reduce the magnitude of I(K) and increase the magnitude of I(Cl), 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 pH(o) = 6.5 than at pH(o) = 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 NaCl-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.