Effect of Na(3)VO(4) on the P State of Nitella translucens

The capacity of sodium orthovanadate to inhibit the plasmalemma H⁺ ATPase of Nitella translucens internodal cells in vivo was tested. Here we show that 1 millimolar vanadate added externally depolarizes strongly and permanently the membrane potential, both in dark and light, to the Nernst potential for potassium consistent with pump inhibition by vanadate. From the results it is clear that the H⁺ ATPase is always active, under light or dark conditions, in contradiction with the widespread idea of pump inactivation by darkness. The changes in conductance for light, dark, and vanadate-induced conditions are analyzed. The effect of dark on membrane passive permeabilities and on the possibility that some plasmalemma channels could be regulated by a phosphorylation-dephosphorylation process is discussed.