Absence of black-white differences in sodium and calcium in platelets.

Consistent differences in sodium transport in red blood cells are observed in blacks compared to whites and have been the basis for speculation regarding physiologic differences in the vascular bed as well. The theoretical link between these metabolic markers and the risk of hypertension generally assumes a secondary effect on calcium. Calcium metabolism in red cells is difficult to study, however, so this proposition has never been tested directly. Given the growing importance of platelets in this area of research, and the availability of sensitive laboratory methods, we carried out a systematic examination of calcium and sodium homeostasis in this cell line among black and white normotensive subjects. No differences were noted in resting cytosolic calcium, mobilizable stores, agonist-induced response, or sodium-calcium exchange. In addition, resting sodium was not different between groups, nor was the increase in sodium induced by ouabain. A correlation of 0.3 was observed between blood pressure and both resting and stimulated cytosolic calcium (P < .05). Red cells may be atypical for studies of calcium and sodium homeostasis, and their relevance for interethnic studies of causal pathways in hypertension should be reconsidered.