DIFFERENTIAL-EFFECTS OF THE PROTEIN-KINASE-C ACTIVATOR PHORBOL 12-MYRISTATE 13-ACETATE ON CALCIUM RESPONSES AND SECRETION IN ADHERENT AND SUSPENDED RBL-2H3 MUCOSAL MAST-CELLS

Adhesion of RBL-2H3 mucosal mast cells to fibronectin-coated surfaces has been linked to changes in secretion and tyrosine kinase activity, me now show that adhesion affects the sensitivity of RBL cells to the protein kinase C activator phorbol 12-myristate 13-acetate (PMA). In s uspended cells, PMA inhibited antigen-induced calcium influx (as measu red by manganese influx) and changes in intracellular free calcium and had complex effects on antigen-stimulated secretion, However, in adhe rent cells PMA had little effect on these responses, Suspended cells o nly secreted in response to thapsigargin if they were co-treated with PMA, while adherent cells secreted in response to thapsigargin alone, The thapsigargin-induced secretion in adherent cells was inhibited by protein kinase C down-regulation and by the protein kinase C inhibitor GF 109203X, but not by calphostin C, We suggest that protein kinase C is constitutively activated in adherent cells, possibly due to modifi cation of the regulatory domain of the enzyme.