Erythrocyte cation metabolism in salt-sensitive hypertensive blacks as affected by dietary sodium and calcium.

The role of dietary salt and calcium on changes in cellular cation metabolism has been evaluated in 11 salt-sensitive hypertensive black adults maintained on the following four metabolic diets for 56 days, 14 days on each diet in a repeated measures format: 356 mg Ca-1000 mg sodium (NA); 356 mg Ca-4000 mg Na; 934 Ca-1000 mg Na; and 934 mg Ca-4000 mg Na. Increasing dietary Na at the lower Ca intake caused significant (P less than 0.05) increases in parathyroid hormone (PTH) and 24-hour cyclic AMP excretion that were associated with significant (P less than 0.01) increases in erythrocyte intracellular calcium (from 5.4 +/- 0.7 to 11.1 +/- 3.7 microM), Ca-ATPase (from 37.2 +/- 2.4 to 42.2 +/- 2.1 pmol/min/10(6) cells) and intracellular sodium (from 220.5 +/- 7.4 to 262.0 +/- 8.3 micrograms/mL) and decreases (P less than 0.05) in Na/K-ATPase (from 1.90 +/- 0.55 to 1.48 +/- 0.47 pmol/min/10(6) cells) and intracellular magnesium (Mg) (from 52.4 +/- 3.5 to 43.8 +/- 2.4 micrograms/mL). Adding calcium to this high sodium diet reversed these effects, whereas adding calcium to the low sodium diet was without significant effect. These results indicate that dietary salt causes increases in intracellular sodium and calcium and that the antihypertensive effect of dietary calcium in salt-sensitive individuals may be attributable in part to preventing this salt-induced elevation in intracellular calcium. This increase in intracellular calcium could be due to the observed increase in PTH levels or to the salt-induced reduction in intracellular magnesium that appears to suppress Na/K-ATPase and thereby increases intracellular sodium.