Ionic Diffusion Through theNitellaCell Wall in the Presence of Calcium

Abstract

Diffusion potentials (concentration and bi- or multi-ionic potentials) in KC1, NaCl, or LiCl solutions have been measured across an isolated cell wall of Nitella, with or without the same concentration of CaCl² on either side of the cell wall. The absolute value of the potentials decreases as the external Ca²⁺concentration increases and it may happen that an inversion of the sign of the concentration potentials results when the external Ca²⁺ solution reaches 1 mM. Dosages of K⁺ and Ca²⁺ in the cell wall have shown that Ca²⁺ easily displaces the monovalent ion from the exchange sites and tends to neutralize the cationic exchanger. However, in most cases, the measured potentials are still more negative than the theoretical potentials which would be set up by a neutral-site membrane in the same conditions. These results suggest that Ca²⁺ largely reduces the discrimination properties of the cell wall between cations and anions.