Sodium and potassium flux rates in normal human leucocytes in an artificial extracellular fluid.

1. Sodium and potassium efflux and influx rates were studied in normal human leucocytes in an artificial extracellular fluid using radioactive isotopes. 2. The rate constant for sodium efflux was 4-2 h-l corresponding to a sodium efflux rate of 487 mmol kg cell dry weight-’ h-l. Approximately three-quarters of this flux was ouabain sensitive. 3. Potassium influx was 346 mmol kg cell dry weight-’ h-l. Approximately twothirds of the potassium influx was ouabain insensitive.