Effect of ouabain on the Ca 2+-dependent increase in K + permeability in depleted guinea-pig red cells

Abstract

1. 1. The hypothesis that the inhibitory action of ouabain on the Ca 2+-dependent increase in K + permeability observed in depleted human red cells is mediated by changes in the intracellular level of ATP was tested by measuring simultaneously the ouabain sensitive K + loss and the concentration of ATP in depleted guinea-pig red cells in the presence and absence of external Ca 2+. 2. 2. The results showed that ouabain has opposite effects on the K + loss. Thus, in the presence of external K +, when the forward running of the Na + pump contributes to the breakdown of ATP, ouabain reduces K + loss, as observed in human red cells; in a K + free, high Na + medium when the pump running backwards induces a net synthesis of ATP (which can be detected in guinea-pig red cells but not in human red cells), ouabain increases K + loss. 3. 3. The results suggest that the action of ouabain is mediated through the changes in the intracellular level of ATP induced by the forward or reverse operation of the Na + pump.