Investigations on the control of ion transport in human erythrocytes. II. Influence of transmembrane potential, exterior surface potential and intracellular pH on the 22Na efflux.

The rate constant of the Na+ efflux of human erythrocytes in isotonic solutions of various ionic strength varied over NaCl concentration was measured. The Na+ efflux remained constant over a wide range of ionic strength. Only under conditions where the transmembrane potential was near O mV, a local minimum could be detected. The rate constant of the ouabain-insensitive part of the Na+ efflux exhibited a strong increase at reduced exterior ionic strength. When reducing the extracellular NaCl concentration and at the same time equivalently increasing the extracellular KCl concentration in solutions of physiological ionic strength, a reduction of the rate constant of the Na+ efflux was found. It was established that an increase of the intracellular pH increases the rate constant of the Na+ efflux. A change of transmembrane potential from -7 to 52 mV at constant intracellular pH had no influence on the Na+ efflux. The change of the exterior surface potential of erythrocytes by preincubation with neuraminidase had no influence on the Na+ efflux in the range of the ionic strength studied.