The effect of external sodium on ouabain-insensitive K influx in fresh human red blood cells

The rate of 42K influx was investigated at various external sodium and ouabain concentrations in human red blood cells. In agreement with earlier reports, in red blood cells not treated with ouabain, Na did not affect K influx when [K]0 was 5.0 mM while it reduced the influx at [K]0 = 0.15 mM. However, Na stimulated 42K influx at both 5.0 mM and 0.15 mM in cells treated with ouabain (1 X 10(-5) M). When external Na concentration was raised from 0 to 72 mM the rate of 42K influx increased at [K]0 = 0.15 mM and at ouabain = 1 X 10(-5) M. The effect of external Na at different ouabain concentrations showed that K influx was inhibited by Na without or with ouabain in less than 5 X 10(-6) M while an increased K influx could be observed with higher ouabain concentrations in the incubation media. The results suggest that in the case of the complete inhibition of ouabain-sensitive K influx the electrochemical gradient of the Na ions may serve as a driving force for the inward movement of potassium.