Abstract
Cardiac glycosides inhibit the sodium pump. However, some studies suggest that nanomolar ouabain concentrations can stimulate the activity of the sodium pump.
In this study, using the Na^+^/K^+^‐ATPase of human erythrocytes, we compared the effect of digoxin, ouabain and an ouabain like‐factor (OLF), on ^86^Rb uptake.
Ouabain concentrations below 10^−9^ M significantly stimulate Rb^+^ uptake, and the maximal increase above base‐line values is 18 ± 5% at 10^−10^ M ouabain. No stimulation is observed in the same conditions by digoxin. OLF behaved like ouabain, producing an activation of Rb^+^ flux at concentrations lower than 10^−9^ M ouabain equivalents (14 ± 3% at 10^−10^ M).
Western blot analysis revealed the presence of both α~1~ and α~3~ pump isoforms in human erythrocytes. Our data confirm the analogies between OLF and ouabain and suggest that Na^+^/K^+^‐ATPase activation may be related to the α~3~ isoform.
In addition, we investigated whether ouabain at different concentrations was effective in altering the intracellular calcium concentration of erythrocytes. We found that ouabain at concentration lower than 10^−9^ M did not affect this homeostasis. Copyright © 2006 John Wiley & Sons, Ltd.