Differences of Ca 2+ regulation in skin fibroblasts from blacks and whites

Black people have a higher propensity than caucasions toward essential hypertension. To explore the possibility that this racial difference relates to cellular Ca 2+ metabolism, we measured 45 Ca 2+ washout and uptake and cytosolic free concentration of Ca 2+ [Ca 2+ ], in serially passed skin fibroblasts from normotensive black and white males. Depending on the experimental conditions, 45 Ca 2+ washout in these cells was described by either two or three exponential functions, whereas 45 Ca 2+ uptake was described only by a two‐exponent function. There were no racial differences in 45 Ca 2+ uptake and washout of unstimulated fibroblasts. However, stimulation by human serum resulted in an increase in the 45 Ca 2+ washout that was higher in fibroblasts from blacks than from whites. The racial differences were expressed primarily by higher values of the apparent washout rate constant (k 1 ) of 45 Ca 2+ from the largest and most rapidly exchangeable cellular pool. The effect of human serum was not related to its origin (blacks vs. whites). In 2 mM Ca 2+ medium and 10% serum from blacks, the respective k 1 (mean ± SEM; × 10 −2 /min) values for fibroblasts from blacks and whites were 89.68 ± 5.23 and 73.29 ± 4.0; in the presence of 10% serum from whites, the k 1 values for cells from blacks and whites were 84.14 ± 2.80 and 76.36 ± 3.23 (overall significance of P .01). In Ca 2+ ‐deficient medium in the presence of 10% human serum, the k 1 for fibroblasts from blacks and whites were 115.57 ± 3.76 and 102.15 ± 3.30 (P < .05). Serum substantially increased the 45 Ca 2+ uptake in fibroblasts from both blacks and whites; however, racial differences were not observed. Basal levels of [Ca 2+ ], were not different in fibroblasts of blacks vs. whites (46.8 ± 6.8 and 43.2 ± 7.1 nM for blacks and whites, respectively). However, the peak response of Ca 2+ transients for cell stimulated by 5% human serum was significantly higher in blacks than whites (blacks = 963 ± 213, whites = 481 ± 162 nM; P = .0286). We conclude that Ca 2+ regulation is different in serum‐stimulated fibroblasts from blacks and whites and that, at least in part, this difference may relate to a greater agonist‐induced mobilization of Ca 2+ in fibroblasts from blacks.