DOES PROTEIN-KINASE-C REGULATE RECEPTOR AGONISTS-MEDIATED ELEVATION IN THE CYTOSOLIC CA2+ IN HUMAN NEUTROPHILS

The feedback regulation of elevated cytosolic free Ca2+ concentrations ([Ca2+](i)) by protein kinase C (PKC) in neutrophils was studied by two approaches. First, the PKC-activity was induced by phorbol 12-myristate 13-acetate (PMA) before the stimulation of Ca2+-signal with N-formyl-methionyl- leucyl-phenylalanine and serum-opsonized zymosan particles. Pretreatment of cells with PMA inhibited agonists-dependent Ca2+-transients. This inhibition was reversed by staurosporine. Second, the PKC-activity was induced simultaneously with the Ca2+-signal by the receptor agonists. In these conditions staurosporine had no effect on the Ca2+-response. In addition, the enhancement of PKC-activity, obtained by accumulating the endogenous PKC-activator diacylglycerol (DAG) with a DAG-kinase inhibitor, failed to change the agonists-stimulated elevations of [Ca2+](i). It is concluded that activation of PKC by PMA inhibits neutrophil Ca2+-responses, whereas receptor-mediated activation of PKC does not yield a negative feedback in elevated[Ca2+](i). (C) 1994 Academic Press, Inc.