Differences of Ca²⁺ 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 Ca²⁺ metabolism, we measured ⁴⁵Ca²⁺ washout and uptake and cytosolic free concentration of Ca²⁺ [Ca²⁺], in serially passed skin fibroblasts from normotensive black and white males. Depending on the experimental conditions, ⁴⁵Ca²⁺ washout in these cells was described by either two or three exponential functions, whereas ⁴⁵Ca²⁺ uptake was described only by a two-exponent function. There were no racial differences in ⁴⁵Ca²⁺ uptake and washout of unstimulated fibroblasts. However, stimulation by human serum resulted in an increase in the ⁴⁵Ca²⁺ 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 (k₁) of ⁴⁵Ca²⁺ 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 Ca²⁺ medium and 10% serum from blacks, the respective k₁ (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 k₁ values for cells from blacks and whites were 84.14 ± 2.80 and 76.36 ± 3.23 (overall significance of P .01). In Ca²⁺-deficient medium in the presence of 10% human serum, the k₁ for fibroblasts from blacks and whites were 115.57 ± 3.76 and 102.15 ± 3.30 (P < .05). Serum substantially increased the ⁴⁵Ca²⁺ uptake in fibroblasts from both blacks and whites; however, racial differences were not observed. Basal levels of [Ca²⁺], 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 Ca²⁺ 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 Ca²⁺ 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 Ca²⁺ in fibroblasts from blacks.