Differences between store-dependent Ca²⁺ fluxes in lymphocytes from African Americans and whites

Objective. To investigate differences between store-dependent Ca²⁺ in African American and white men. Method. Thapsigargin, a potent and specific inhibitor of the sarco(endo)plasmic reticulum Ca²⁺-ATPase, was used as a probe to elicit store-dependent Ca²⁺ fluxes. Treatment with this agent caused a rise in the cytosolic free Ca²⁺ due to the egress of Ca²⁺ from thapsigargin-sensitive Ca²⁺ stores and the acceleration of external Ca²⁺ influx through store-dependent Ca²⁺ channels. Design. Lymphocytes were obtained from 22 African Americans and 23 whites. These cells were subjected to thapsigargin treatment and changes in the cellular Ca²⁺ profiles were monitored. Results. Both in Ca²⁺-free and in Ca²⁺-containing media the increases in cytosolic free Ca²⁺ concentrations after thapsigargin treatment were greater in lymphocytes from African Americans than they were in those from whites. The greater levels of cytosolic Ca²⁺ concentration were coupled with higher rates of Ca²⁺ extrusion in thapsigargin-treated lymphocytes from African Americans. Conclusions. These findings suggest that store-dependent Ca²⁺ fluxes are greater in lymphocytes from African Americans than they are in those from whites. This phenomenon increases the Ca²⁺ turnover rate and might augment the sensitivity to agonists acting through Ca²⁺ signaling systems, thereby predisposing African Americans to essential hypertension.