Efflux of 45CA2+ from human fibroblasts in response to serum or growth factors

Abstract

Previous studies have indicated that intracellular Ca²⁺is involved in fetal bovine serum (FBS)‐ or growth factor (GF)‐stimulated Na⁺ influx in human foreskin fibroblasts (HSWP). In the present study, ⁴⁵Ca²⁺ efflux from serum‐deprived HSWP cells was measured in response to 10% FBS or GF [lys‐bradykinin, vasopressin, epidermal growth factor, and insulin]. Efflux data were analyzed using a computer program and the best fit indicated the presence of three Ca²⁺ compartments: a compartment (C₁) with a very fast turnover rate, one (C₂) with a fast turnover rate, and one (C₃) with a slow turnover rate. When serum‐deprived cells were treated with 10% FBS, efflux from C₂ and C₃ increased significantly (p>0.05). Similar effects on efflux were observed when serum‐deprived cells were treated with individual GFs. Combination of the four GFs produced a higher stimulation than any single factor and a response that was equal to that for FBS. On the other hand, when cells were serum‐treated in the presence of the intracellular Ca²⁺ antagonist, 8‐(N‐N, diethylamino)‐octyl 3,4,5‐trimethoxybenzoate (TMB‐8), ⁴⁵Ca²⁺ efflux from C₂ was substantially reduced. Finally, when cells were treated with the Na⁺ transport inhibitor amiloride, there was no significant effect on serum‐stimulated Ca²⁺ efflux. These results are consistent with a FBS‐ or GF‐induced mobilization of Ca²⁺ that can be blocked by intracellular Ca²⁺ antagonists, and support the hypothesis that the action of these agents on Na⁺ influx may be via their effects on intracellular Ca²⁺.