Modulation of erythrocyte Na transport pathway(s) by excess Na intake

Different Na transport pathways were studied in the erythrocytes of 10 normotensive subjects who received 240 meq/day of Na in excess of their usual diet. In most of these subjects the maximal rate (Vmax) of the Na,K pump and the Na,K-cotransport system was markedly decreased on the first day of the diet. In some of these subjects, excess Na intake induced an increase in the apparent affinity for internal Na for the Na,K pump and the Na,K-cotransport system. The decrease in the Na,K pump fluxes was not concomitant to that of the co-transport system and not accompanied with an increase in blood pressure or cation concentration in the plasma. Interestingly, the apparent affinity for internal Li of the Li-Na exchange was markedly increased without alteration of the Vmax. The passive permeability for Na and the cellular Na content were not altered by excess Na intake. Ouabain and bumetanide at low concentrations respectively induced an increase in the apparent affinity for internal Na of the Na,K pump and the Na,K- cotransport system. These results are similar to those observed after excess Na intake. These later agree with the hypothesis that Na homeostasis regulates some endogenous factors with ouabain-like and furosemide-like properties that might contribute to the regulation of cellular Na handling.