Red blood cell Na+ transport as a predictor of blood pressure response to Na+ load in young blacks and whites.

The present study was designed to investigate the role of abnormalities in red blood cell sodium-potassium-chloride (Na-K-Cl) cotransport and Na+ pump as predictors of the pressor response to chronic oral Na+ loading in young whites and blacks. Subjects were healthy adults from 18 to 23 years of age and included normotensive whites (n = 24) and normotensive blacks (n = 35). Red blood cell transport studies were performed before Na+ loading. The Na+ load consisted of 10 g NaCl daily added to the usual diet. A sodium-sensitive response was defined as an increase of 5 mm Hg or more in mean arterial pressure after the Na+ load; a sodium-insensitive response was a less than 5 mm Hg increase in mean arterial pressure. A sodium-sensitive response occurred in 16% of whites and 57% of blacks. Black subjects have a significantly lower (p less than 0.005) maximal rate of furosemide-sensitive Na+ efflux and a higher Km for cellular Na+ (p less than 0.05) to activate Na-K-Cl cotransport than white subjects. Normotensive blacks with sodium-sensitive blood pressure response had a higher Km (14.4 +/- 6 mmol/l cell, n = 17, mean +/- SD) to activate the cotransport than sodium-insensitive blacks (9.9 +/- 3.7 mmol/l cell, n = 13, p less than 0.001). Normotensive whites had a significantly lower red blood cell Na+ content (p less than 0.05) and a higher maximal rate of cotransport (p less than 0.005) than young normotensive blacks.(ABSTRACT TRUNCATED AT 250 WORDS)