Effects of an intravenous saline load on erythrocyte sodium transport in normal human subjects.

The effects of a 2 litre intravenous infusion of saline (0.9% NaCl solution) over 3 h on erythrocyte transmembrane sodium transport were studied in 12 normal human subjects. After saline infusion a significant (P less than 0.01) reduction of both outward Na+,K+ pump- and Na+,K+ cotransport-mediated Na+ effluxes was observed. The Na+,Li+ countertransport rate and the passive Na+ permeability did not change. The incubation of the subjects' erythrocytes, obtained on a separate occasion, with their own plasma taken after the saline infusion, induced an inhibition of both Na+,K+ pump and Na+,K+ cotransport outward sodium fluxes. The percentage decrease after incubation was closely correlated with the percentage reduction induced by the saline infusion in vivo (r = 0.93 for the pump and r = 0.96 for cotransport; P less than 0.01). These data suggest that extracellular fluid volume expansion affects the release of circulating factors modulating sodium transport by the Na+,K+ pump and by Na+,K+ cotransport.