BIOELECTRIC POTENTIALS IN VALONIA

Abstract

The P.D. across the protoplasm of V. macrophysa is decreased by lowering and increased by raising the concn. of KCl in artificial sea water bathing the cell. P.D.-time curves with KCl-rich sea water resemble those with Valonia sap (See B. A. 5(5): Entry 13625). Neither the P.D. with natural sea water nor the magnitude of the initial rise in P.D. when natural sea water is replaced by KCl-rich sea water is appreciably affected by varying the reaction of the external soln. between pH 5 and pH 10; the shape of the P.D.-time curve, however, undergoes changes indicating that K enters Valonia protoplasm more rapidly from alkaline than from acid solns. The initial rise in P. D. can be calculated satisfactorily by means of the Planck or the Henderson equation, assuming that this P.D. represents a diffusion potential in a (non-aqueous) external surface layer of the protoplasm, where ionic mobilities may be supposed to differ greatly from their values in water. Using the relative mobilities for Na+ (0.20) and for Cl- (1.00) determined from earlier experiments (See B. A. 6: 15476) an average value for the apparent relative mobility of K+ is found to be approx. 20. Calculation as phase-boundary potentials proved unsatisfactory.