MUCIN SECRETION BY T84 CELLS - STIMULATION BY PKC, CA-2-KINASE ACTIVATED BY CA-2+ IONOPHORE(, AND A PROTEIN)

T84 adenocarcinoma cells were stimulated to secrete mucin by the phorb ol ester phorbol 12-myristate 13-acetate (PMA) and Ca2+ ionophores A23 187 and ionomycin. In Ca2+-containing media, maximal stimulation by PM A was significantly inhibited by staurosporine, but maximal A23187-sti mulated secretion was not affected. Downregulation of protein kinase C (PKC) reduced maximal PMA-stimulated secretion without affecting the response to A23187. Thus PKC activation is not required for maximal Ca 2+-mediated mucin secretion. PMA stimulated secretion in low-Ca2+ medi a, with and without intracellular chelation of Ca2+ by ,2-bis(2-aminop henoxy)ethane-N,N,N',N'-tetraacetic acid. Surprisingly, Ca2+ ionophore s also stimulated secretion under the same circumstances. Persistent A 23187-stimulated secretion was strongly inhibited by the protein kinas e inhibitors staurosporine and H-7. Secretion in Ca2+-containing media was also inhibited at submaximal levels of Ca2+-ionophore stimulation . These results indicate that PKC and Ca2+ stimulate mucin exocytosis independently. Ca2+ ionophores also stimulate secretion via a protein- kinase dependent pathway. Enhancement of protein kinase inhibition at lower Ca2+ concentrations suggests that the response could be mediated by a Ca2+ ionophore-induced depletion of an intracellular Ca2+ pool.