Membrane Potential in Phaeoceros laevis

Abstract

Gametophyte cells of P. laevis (L.) Prosk. have vacuole electric potentials (PD) of about -175 mV; the steady PD is not affected by light but small transient PD result after changing from light to darkness or darkness to light. The PD is more negative than the Nernst potentials for any of the permeating ions. Changes in the concentration of any one of the external ions between 0.1 and 10 mM have only a very small effect on the PD. Increases in external pH cause the PD to depolarize by a few mV. Azide, 2,4-dinitrophenol and NH4Cl each cause rapid and reversible depressions of the PD; the effects of these agents are similar in magnitude in the light and in the dark. Anoxia depolarizes the PD by about 30 mV in the light and by about 60 mV in the dark. Ouabain and 3-(3,4-dichlorophenyl)-1,1-dimethylurea have no effects on the PD. Apparently the membrane potential is controlled by an electrogenic efflux pump, possibly for H+. It is concluded that the source of energy for the pump is respiration and not photo- synthesis.