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(Hypertension. 1995;25:377-383.)
© 1995 American Heart Association, Inc.

Articles

Increased Calcium Stores in Platelets From African Americans

Jwa Hwa Cho; Frederic Nash; Zoltan Fekete; Masayuki Kimura; John P. Reeves; Abraham Aviv

From the Hypertension Research Center, Departments of Internal Medicine and Physiology, University of Medicine and Dentistry of New Jersey, Newark.

Correspondence to Abraham Aviv, MD, Hypertension Research Center, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, 185 S Orange Ave, MSB F-464, Newark, NJ 07103-2714.

Abstract Differences in cation transport have been observed between African Americans and whites. These differences may underlie the increased predisposition of African Americans to essential hypertension. To further explore these racial differences, we used platelets as a cellular model for calcium regulation. We measured ⁴⁵Ca fluxes in platelets from 21 African American and 25 white men. Additionally, using fura 2, we measured cytosolic free calcium levels in resting platelets and platelets treated with ouabain and thrombin. Platelet ⁴⁵Ca uptake was described by two exchangeable pools: a small, rapidly exchangeable pool and a larger, slowly exchangeable pool. Both pools were larger in platelets from African Americans than from whites (263 versus 185 pmol per 1x10⁸ platelets for the rapidly exchangeable pool, P<.05; 744 versus 532 pmol per 1x10⁸ platelets for the slowly exchangeable pool, P<.01). ⁴⁵Ca washout was described by a rapidly exchangeable pool and a static pool. The former was also higher in platelets from African Americans than from whites (246 versus 202 pmol per 1x10⁸ platelets, P<.01). The cytosolic free calcium concentrations in resting platelets were lower in African Americans than in whites. After treatment with ouabain and thrombin, the sustained posttransient levels of cytosolic free calcium increased to a greater extent in platelets from African Americans (46.7 nmol/L) than from whites (34.5 nmol/L, P=.033). Platelets from African Americans demonstrate higher intracellular calcium stores than platelets from whites. This racial difference could explain the sensitivity of African Americans to vasoactive agents acting through calcium mobilization from intracellular stores and cytosolic calcium.

Key Words: calcium pump • calcium channels • whites • hypertension, essential • ouabain • parathyroid hormone • thrombin

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