A study of passive potassium efflux from human red blood cells using ion-specific electrodes

Abstract

Summary. Using ion-specific electrodes, the potassium leakage induced by ouabain in human erythrocytes can be measured continuously and precisely near physiological conditions. Upon small additions of isotonic sucrose solution to a suspension of red cells in physiological saline the passive potassium efflux increases proportionally to the chloride ratio. The same result is obtained upon addition of hypertonic sucrose solution, suggesting that neither osmolarity nor intracellular concentrations have any influence on the passive potassium efflux. The independence of the potassium efflux and osmolarity can be verified by addition of a penetrating substance like glucose to the cell suspension. Adding water or hypertonic sodium chloride solution shows that the potassium efflux increases slightly in more concentrated salt solutions. Inasmuch as it can be interpreted as a pure ionic strength effect, this result supports the hypothesis of independence of potassium efflux and intracellular concentrations. The results of this investigation together with other studies show that the passive permeability of the human red blood cell to potassium depends uniquely on the membrane potential near physiological conditions, while it depends on parameters such as pH or concentrations for large membrane potentials. This suggests that two different mechanisms of transport might be involved: one would control the permeability under normal conditions; the other would represent a leak through the route normally used by anions and become important only under extreme conditions.Because it is readily available in great quantities and its structure is simpler than that of other cells, the erythrocyte is an object of choice for the study of cell membrane properties. The active pumping of sodium and potassium across the red cell membrane has been demonstrated for some time [13] and it is probably now the best studied of all active transport processes.A necessary lemma to the complete elucidation of active transport mechanisms in the red cell membrane is the explanation of the cell's passive transport properties. How does the red cell discriminate between ions and, above all, between anions and cations? What parameters determine the

Mechanism of the increase in cation permeability of human erythrocytes in low-chloride media. Involvement of the anion transport protein capnophorin.

“…He proposed that as the pH increases in these channels, hydrogen ions are liberated, and finally, at very high pH, the charge barrier is so diminished or reversed as to allow the passage of cations. Mond (1927), Passow (1964), Wilbrandt and Schatzmann (1960), La Celle and Rothstein (1966), Donlon and Rothstein (1969), and Morel (1973) found that the rates of cation efflux increased at low external anion concentrations . This was not due solely to an increase in the driving force for cation efflux because of the change in membrane potential, but also represented a true increase in the apparent cation permeability .…”