INCREASED CALCIUM STORES IN PLATELETS FROM AFRICAN-AMERICANS

Differences in cation transport have been observed between African Ame ricans and whites. These differences may underlie the increased predis position of African Americans to essential hypertension. To further ex plore these racial differences, we used platelets as a cellular model for calcium regulation. We measured Ca-45 fluxes in platelets from 21 African American and 25 white men. Additionally, using fura 2, we meas ured cytosolic free calcium levels in resting platelets and platelets treated with ouabain and thrombin. Platelet Ca-45 uptake was described by two exchangeable pools: a small, rapidly exchangeable pool and a l arger, slowly exchangeable pool. Both pools were larger in platelets f rom African Americans than from whites (263 versus 185 pmol per 1 x 10 (8) platelets for the rapidly exchangeable pool, P<.05; 744 versus 532 pmol per 1x10(8) platelets for the slowly exchangeable pool, P<.01). Ca-45 washout was described by a rapidly exchangeable pool and a stati c pool. The former was also higher in platelets from African Americans than from whites (246 versus 202 pmol per 1 x 10(8) platelets, P<.01) . The cytosolic free calcium concentrations in resting platelets were lower in African Americans than in whites. After treatment with ouabai n and thrombin, the sustained posttransient levels of cytosolic free c alcium increased to a greater extent in platelets from African America ns (46.7 nmol/L) than from whites (34.5 nmol/L, P=.033). Platelets fro m African Americans demonstrate higher intracellular calcium stores th an platelets from whites. This racial difference could explain the sen sitivity of African Americans to vasoactive agents acting through calc ium mobilization from intracellular stores and cytosolic calcium.