Kinetics of Na+ and K+ transport in red blood cells of Dahl rats. Effects of age and salt.

Blood pressure response to chronic high salt intake and kinetics of red blood cell Na+ and K+ (Rb+) transport were studied in salt-sensitive (DS) and salt-resistant (DR) Dahl rats fed a high salt diet (8% NaCl) for 7 weeks from the fifth (young), 12th (adult), or 23rd (old) week of age. The kinetics of ouabain-sensitive Rb+ uptake and Na+ extrusion were determined in Na+ media as a function of both intracellular Na+ (Na+i, 2-8 mmol/l cells) and extracellular Rb+ (Rb+o). In addition, the kinetics of furosemide-sensitive Rb+ uptake (related to Rb+o) and the magnitude of the Na+ and Rb+ leaks were assessed. High salt induced hypertension in young and adult but not in old DS rats although red blood cell Na+ was slightly increased in all age groups of DS rats fed a high salt diet. The kinetic parameters of the Na(+)-K+ pump were similar in DS and DR rats fed a low salt diet. Ouabain-sensitive transport rates were not suppressed in erythrocytes of salt hypertensive Dahl rats. Maximal velocities of the Na(+)-K+ pump (related to Na+i) decreased significantly with age in all groups except in DS rats fed a high salt diet. This was compensated by an age-dependent increase in the affinity for Na+i so that no substantial differences in transport rates between young and old rats were seen at physiological cell Na+ and plasma K+ levels.(ABSTRACT TRUNCATED AT 250 WORDS)