in? and Dentistry of N e w lersey, Newark, Ncw lersey 07 103 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 Ca'+ [Ca2+ Ii in serially passed skin fibroblasts from normotensivc 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 4 5 ~~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 (kl) of 45Ca'+ 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 m M Ca2 ' medium and 10% serum from blacks, the respective k, (mean * SEM; x 1 O-'/rnin) values for fibroblasts from blacks and whites were 89.68 2 5.23 and 73.29 * 4.0; in the presence of 10% serum from whites, the k, values for cells from blacks and whites were 84.14 2 2.80 and 76.36 2 3.23 (overall significance of P < .01). In Ca'+-deficient medium in the presence of 10% human serum, the k, for fibroblasts from blacks and whites were 115.57 * 3.76 and 102.15 f 3.30 (P < .05). Serum substantially increased the