EFFECT OF INTRACELLULAR PH ON THE LIGHT-INDUCED POTENTIAL CHANGE AND ELECTROGENIC ACTIVITY IN TONOPLAST-FREE CELLS OF CHARA-AUSTRALIS

Effects of the intracellular H+ concentration on the membrane potential and membrane resistance of tonoplast-free cells of Chara australis were examined under light and dark conditions. Cells were made tonoplast-free by perfusing the vacuole with media containing 5 mM EGTA and 30 mM buffers of various pH values. The electrogenic pump was stopped by removing the intracellular ATP. The ATP-dependent part of the membrane potential was large at pH1 6.2 and 6.9, but decreased in both the acidic (pH1 5.1, 5.7) and alkaline (pH1 7.9, 8.7) ranges. Assuming that the putative electrogenic H+ pump acts solely as a current source, we estimated the current and the work done by the pump. Both the current and the work were at a maximum at pH1 6.9, but decreased to some extent at pH1 7.9-8.7 and decreased greatly at pH1 5.7-5.1.Light caused a significant membrane hyperpolarization at pH1 6.2-7.9, but only a slight hyperpolarization at pH1 5.1, 5.7 and 8.7. The presence of light-induced hyperpolarization at pH1 lower than 6.2 suggests that acidification of the cytoplasm upon illumination does not cause activation of the putative H+ pump.Membrane resistance was very high at pH1 5.1 and 5.7 and very low at pH1 8.7. The very high Rm values at pH1 5.1 and 5.6 are believed to be related to inhibition of the activity of the pump. © 1979 Oxford University Press.