Effects of bicarbonate and thiocyanate on fluxes of Na and K, and on glucose metabolism of actively transporting human red cells.

Abstract

AbstractIt has been shown in a previous work that sodium influx is trebled, whereas potassium efflux is slightly reduced, when erythrocytes are suspended in a 142 mM bicarbonate medium containing ouabain. The present work deals with the active transport of sodium and potassium occurring in the presence of 142 mM bicarbonate (38° C, pH 7.40). Sodium influx and potassium efflux were unaffected by the removal of ouabain, whereas sodium efflux, potassium influx, and glucose metabolism were all strongly stimulated. The relation between ouabain sensitive ion transport and the calculated extra formation of ATP was 3.1 moles Na/mole ATP and 2.3 moles K/mole ATP, in agreement with values previously found on red cells transporting Na and K in plasma. Red cells incubated in the bicarbonate medium accumulated potassium until extracellular potassium concentration had been reduced to 1.8–2 mM. The normal volume regulation of the cells was severely interfered with, because accumulation of sodium and potassium was accompanied by a net flux of water of 6 g per meq cation. All effects observed could be interpreted to be secondary to the increased sodium influx, leading to an increase of intracellular sodium concentration, which in turn stimulated active cation transport, thereby accelerating the rate of ATP turn‐over. The properties of the ouabain sensitive transport mechanism were not affected by the presence of bicarbonate.Both potassium efflux and sodium influx are increased by 200–300 per cent in the presence of 120 mM thiocyanate. It was found, however, that active cation transport is not stimulated in a 120 mM thiocyanate medium. On the contrary the ouabain sensitive ion transport was steadily decreasing during incubation in spite of conditions otherwise favouring transport of Na and K, i.e. increasing extracellular potassium and intracellular sodium concentrations.