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  • Title: Characterization of Na(+)-K+ homeostasis of cultured human skin fibroblasts in the presence and absence of fetal bovine serum.
    Author: Hopp L, Lasker N, Bamforth R, Aviv A.
    Journal: J Cell Physiol; 1992 May; 151(2):427-32. PubMed ID: 1572913.
    Abstract:
    Previously, we demonstrated that removal of fetal bovine serum (FBS) from the medium of human skin fibroblasts resulted in an accelerated 86Rb+ washout, decreased cellular K+, and increased Na+ contents. In the present study we examined the mechanism underlying these changes. The efflux rate constant for 86Rb+, and the cellular contents of Na+ and K+ were measured. Verapamil (K1/2 = 15 microM) and chlorpromazine (K1/2 = 1 microM) reduced by approximately 70% the increased 86Rb+ washout evoked by FBS removal. The effect of the two drugs was additive at low, but not high, concentrations. Verapamil and chlorpromazine also attenuated the decrease in cellular K+ content and prevented the increase in cellular Na+ content associated with FBS depletion. Bumetanide (50 microM) was only partially effective in offsetting the enhanced 86Rb+ efflux and was completely without any effect on the cellular Na+ and K+ changes induced by FBS removal. In the presence of FBS, A-23187 produced a slight and transient increase of the 86Rb+ washout. The protein kinase C activator phorbol 12-myristate 13-acetate enhanced the 86Rb+ efflux in FBS-containing medium for a prolonged period but this increase was only a fraction of that caused by serum removal. Cellular Na+ and K+ contents were not changed by the phorbol ester. We conclude that FBS removal raises the cellular Na+ content, and enhances 86Rb+ efflux, through a calmodulin-dependent pathway activated by calcium influx.
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