Sodium and Potassium Concentration and Transmembrane Fluxes in Leukocytes

Reported values for the potassium to sodium ratio in white blood cells range from less than 1 to about 4. This marked variability might be explained by in vitro cation shifts induced by extraordinarily high cation permeability. To test this hypothesis, human leukocytes from 5 ml of blood were maintained in plasma at 37°C and separated by differential centrifugation in specially devised microtubes, within less than 30 min after sampling. Intracellular water content was determined with tritiated water, and trapped plasma with ¹⁴C-sucrose. Under these conditions the intracellular concentration of potassium in human leukocytes was 120 SD ± 7 meq/liter cell water and of sodium 16 SD ± 5 meq/liter cell water, and the resultant ratio was higher than 7. Values in the same range were obtained in rabbit leukocytes and in polymorphonuclear granulocytes isolated from peritoneal exudate in guinea pigs. To determine the cation permeability of these white cells, unidirectional fluxes of potassium and sodium were measured with ⁴²K and ²²Na. All of these fluxes were in a range from 1.2 to 2.7 meq/liter/min, values more than 50 times faster than those observed in erythrocytes. When active fluxes were inhibited by ouabain, potassium loss and sodium gain occurred at an initial rate of about 0.7 meq/liter/ min. Marked changes also occurred upon incubation at low temperature. These very rapid fluxes demand rigid control of environmental conditions for accurate measurement of intracellular cations in leukocytes.