Na-K-C1 cotransport and Na pump in red cells of young blacks and blood pressure response to salt loading.

The functional operation of Na and K fluxes, mediated by the furosemide-sensitive (FS) Na-K-C1 cotransport and the ouabain-sensitive Na pump, was studied in a representative young (18-22 years) black population. Cation fluxes (mumol/L cell X hour = FU) were studied prior to salt loading; results were compared with the blood pressure response to chronic oral salt loading. All subjects (n = 26) took 10 g/day NaC1 plus their usual diets for 14 days. A mean arterial blood pressure increase higher than 5 mmHg was considered a sodium-sensitive (SS) response; a response lower than 5 mmHg was considered sodium-insensitive (SI). The Km for Nac to stimulate FS Na efflux was significantly greater in SS (SS = 13.8 +/- 1.39 mmol/L cells, n = 15; SI = 8.5 +/- 0.8 mmol/L cells, n = 11; p less than 0.001). Inward cotransport of Na and K was also studied at constant Nac (13 mmol/L cells) and incubation of 140 mM Na and 4 mM K. No significant differences were found in the Vmax of outward FS Na and K efflux, FS86 Rb, Na influx, net Na movement (efflux minus influx), and the Na/K ratio of inward cotransport. Several parameters of the ouabain-sensitive Na pump (Vmax of the Na efflux, Rb influx, Na/K coupling ratio (2.2), and fresh Nac) were found to be similar in both groups. The results indicate that in young blacks, the Na sensitivity of the blood pressure may be associated with lower affinity for internal Na of the outward Na-K-C1 cotransport system.