Protein kinase C activator PMA reduces the Ca2+ response to antigen stimulation of adherent RBL-2H3 mucosal mast cells by inhibiting depletion of intracellular Ca2+ stores

Activation of protein kinase C has been shown to reduce the Ca2+ responses of a variety of cell types. In most cases, the reduction is due to inhibition of Ca2+ influx, but acceleration of Ca2+ efflux and inhibition of Ca2+ store depletion by protein kinase C activation have also been described. For adherent RBL-2H3 mucosal mast cells, results from whole-cell patch clamp experiments suggest that protein kinase C activation reduces Ca2+ influx, white experiments with intact, fura-2-loaded cells suggest that Ca2+ influx is not affected. Here we present single-cell data from Ca2+ Imaging experiments with adherent RBL-2H3 cells, showing that antigen-stimulated Ca2+ responses of phorbol 12-myristate 13-acetate (PMA)-treated cells are more transient than those of control cells. PMA also reduced the response to antigen in the absence of extracellular Ca2+, indicating that depletion of intracellular Ca2+ stores is inhibited. If PMA was added after stores had been depleted by thapsigargin, a small decrease in [Ca2+](i) was observed, consistent with a slight inhibition of Ca2+ influx. However, the major effect of PMA on the antigen-stimulated Ca2+ response is to inhibit depletion of intracellular Ca2+ stores. We also show that inhibition of protein kinase C did not enhance the Ca2+ response to antigen, suggesting that inhibition of the Ca2+ response by activation of protein kinase C does not contribute to the physiological response to antigen. J. Cell. Physiol. 181:113-123, 1999. (C) 1999 Wiley-Liss Inc.