Study on the dehydrating effect of the red cell Na+/K+-pump in nystatin-treated cells with varying Na+ and water contents

Using the antibiotic Nystatin, we have developed a systematic method for the preparation of red blood cells with independently selected levels of intracellular Na⁺ concentrations and water content. Such cells provided an experimental model to study the effect of Na⁺/K⁺ pump stimulation on red cell water content. Even in initially dehydrated cells, stimulation of the Na⁺/K⁺ pump by elevated intracellular Na⁺ caused subsequent further loss of cell water. Cell water loss was reflected in decreased monovalent cation content per unit mass of hemoglobin and by a shift in the density distribution of the cell populations to higher densities on discontinuous Stractan gradients. We conclude that the 3 Na_out⁺ : 2 K_in⁺ stoichiometry of the Na⁺/K⁺ pump results in a net desalting effect with increased pump activity. Under the conditions of these experiments, the cell appears to have no effective mechanism to compensate for a net loss of ions and water.