Antigen-induced breakdown of membrane phospholipids in basophilic RBL-2H3 cells, appeared to be mediated by Gz-like protein and a tyrosine kinase, and possibly regulated by a phosphatase. Other stimulants, for example, adenosine analogs or carbachol, in RBL-2H3 cells transfected with the gene for the muscarinic ml receptors, operated exclusively through G-proteins to activate phospholipase C and other phospholipases. The ensuing events, however, such as mobilization of intra- and extra-cellular Ca2+, activation of protein kinase C and exocytosis appeared to be identical for all stimulants. In particular, all stimulants recruited Ca2+ from the same intracellular pool of Ca2+ and utilized the same Ca2+-influx mechanism. Studies with inhibitors and purified preparations of recombinant isozymes of protein kinase C in permeabilized RBL-2H3 cells revealed that exocytosis was dependent on both an elevated [Ca2+]i and activation of protein kinase C. In washed permeabilized cells, the secretory response to antigen could be fully reconstituted by buffering [Ca2+]i at 1 microM and addition of nM concentrations of the beta or delta isozymes of protein kinase C.
