Regulation of the H+ pump activity in the plasma membrane of internally perfused Chara corallina

The role of cytoplasm for the maintenance of the H+ pump activity in Chara corallina internodal cells was examined by the intracellular perfusion tech nique. Cytoplasm-rich and -poor states were obtained by changing the perfus ion time, short-term (less than 2 min) and long-term (more than 5 min), res pectively. A large portion of cytoplasm was left hy short-term perfusion hu t most of the cytoplasm was removed by long-term perfusion, The activities of the H+ pump of these two different conditions were examined by measuring current-voltage relation (I-V curve) and conductance-voltage relation (G-V curve) under voltage clamp conditions. The H+ pump conductance decreased t o 37%, 9% and zero by short-term, long-term and hexokinase perfusion, respe ctively, whereas the passive channel conductance decreased to 71%, 39% and 73% by short-term, longterm and hexokinase perfusion, respectively. On the other hand, the electromotive-force of the H+ pump (similar to -260 mV) and the passive channel (similar to -130 mV) were not affected by either short - or long-term perfusion, It is indicated that the cytoplasm plays an essen tial role to regulate the activity of both the H+ pump and the passive chan nel together with ATP.