Sodium movements in high-sodium beef red cells: properties of a ouabain-insensitive exchange diffusion.

1. The relative importance of the Na efflux components in beef red cells has been evaluated. The component which is insensitive to ouabain, which does not require external K but depends on the presence of external Na, accounts for about 90% of the total Na efflux.2. The experiments reported in this paper are consistent with the presence of an ouabain-insensitive Na(+)-Na(+) exchange process accounting for this ouabain-insensitive external Na dependent efflux.3. A strictly parallel behaviour of influx and efflux is observed when the pH is altered. The exchange diffusion process is inhibited over 90% by a decrease in pH from range pH 8.0-5.5.4. Both Na efflux and influx are markedly increased by raising the temperature from 27 to 37 degrees C.5. Energy depleted cells and fresh cells behave similarly in respect to Na movements. In depleted resealed ghosts, a large Na-dependent efflux occurs. No chemical energy and no special nucleotide is required for the Na(+)-Na(+) exchanges.6. When the external or internal Na concentrations are changed, a parallel behaviour of influx and efflux is observed.7. The relation between the magnitude of the exchange diffusion flux and the external or internal Na concentration fits quite well the Michaelis-Menten equation suggesting that only one Na(+) reacts with the transport mechanism. The affinity for Na is lower however at the outer surface than at the inner border of the membrane.8. The relation between this exchange process, the ouabain-insensitive Na-Na exchanges found in human red cell, and Ussing's model of exchange diffusion is discussed.