Lack of difference in oxalate-dependent Ca2+ uptake by membrane homogenate of African-American and white subjects.

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In order to further characterize previously described racial differences in intracellular Ca2+ homeostasis, the activity of sarcoplasmic-endoplasmic reticulum Ca2+-ATPase was measured in cultured skin fibroblasts from normotensive African-Americans and whites. Cells originated from apparently healthy, normotensive African-American (n = 15) and white (n = 15) subjects. The activity of the sarcoplasmic-endoplasmic reticulum Ca2+-ATPase was measured by: 1) oxalate-dependent only, and 2) oxalate-dependent, thapsigargin-sensitive 45Ca2+ uptake of membrane homogenates. Over 90% of the oxalate-dependent 45Ca2+ uptake was thapsigargin-sensitive. There was no detectable racial difference in the sarcoplasmic-endoplasmic reticulum Ca2+-ATPase activity with either technique. It is concluded that the previously described higher cellular Ca2+ turnover and larger cellular stores of exchangeable Ca2+ in cells from African-Americans versus whites are not due to changes in the sarcoplasmic-endoplasmic reticulum Ca2+-ATPase itself. The findings do not exclude possible increased activity of this enzyme in intact cells of African-Americans where regulatory mechanisms not present in the membrane preparation may operate.