Regulation of the plasma membrane potential in Pneumocystis carinii

Many protists use a H- gradient across the plasma membrane, the proton motive force, to drive nutrient uptake. This force is generated in part by the plasma membrane potential (Delta Psi). We investigated the regulation of the Delta Psi in Pneumocystis carinii using the potentiometric fluorescent dye bisoxonol. The steady state Delta Psi in a buffer containing Na+ and K+ (standard buffer) was found to be -78 +/- 8 mV. In the absence of Na+ and K+ (NMG buffer) or Cl- (gluconate buffer), Delta Psi was not significantly changed suggesting that cation and anion conductances do not play a significant role in the regulation of Delta Psi in P. carinii. The Delta Psi was also not affected by inhibitors of the Na+/K+ ATPase, ouabain (1 mM), and the K+/H+-ATPase, omeprazole (1 mM). In contrast, inhibitors of the plasma membrane H+-ATPase, dicyclohexylcarbodiimide (100 mu M). N-ethylmaleimide (100 mu M) and diethylstilbestrol (25 mu M), significantly depolarized the Delta Psi to -43 +/- 7, -56 +/- 5 and -40 +/- 12 mV, respectively. The data support that the plasma membrane H+-ATPase plays a significant role in the regulation of Delta Psi in P. carinii. (C) 2000 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.