HUMAN-PLASMA CONTAINS LOW-MOLECULAR WEIGHT FACTORS WHICH STIMULATE ACTIVE SODIUM-TRANSPORT IN ERYTHROCYTES

Abstract The aim of this study was to establish whether differences in sodium efflux rate constants ( K e ) in human erythrocytes occur when artificial media are compared with plasma. Using a 22 Na tracer method, a mean total K e of 0.49 ± 0.10 h −1 and significantly ( p K e values in Hanks' solution (0.43 ± 0.08 h −1 ) and Basic Salt Solution (0.37 ± 0.07 h −1 ) were observed. Exhaustive dialysis of plasma against Hanks' solution over a membrane with relative molecular mass cut-off of 1000 Da resulted in a decrease of the plasma total K e value to that measured in Hanks' solution. After equilibrium dialysis of plasma against Hanks' solution a decrease of total K e was found in plasma and an increase of the K e in Hanks' solution was measured. The data suggest the presence of an excess of dialyzable, active sodium transport stimulating plasma factor(s) with relative molecular mass below 1000 Da.