Ca21 and protein kinase C activation of mucin granule exocytosis in permeabilized SPOC1 cells

Scott, C. E., Lubna H. Abdullah, and C. William Davis. Ca21 and protein kinase C activation of mucin granule exocytosis in permeabilized SPOC1 cells. Am. J. Physiol. 275 (Cell Physiol. 44): C285–C292, 1998.—Mucin secretion by airway goblet cells is under the control of apical P2Y2, phospholipase C-coupled purinergic receptors. In SPOC1 cells, the mobilization of intracellular Ca21 by ionomycin or the activation of protein kinase C (PKC) by phorbol 12myristate 13-acetate (PMA) stimulates mucin secretion in a fully additive fashion [L. H. Abdullah, J. D. Conway, J. A. Cohn, and C. W. Davis. Am. J. Physiol. 273 (Lung Cell. Mol. Physiol. 17): L201–L210, 1997]. This apparent independence between PKC and Ca21 in the stimulation of mucin secretion was tested in streptolysin O-permeabilized SPOC1 cells. These cells were fully competent to secrete mucin when Ca21 was elevated from 100 nM to 3.1 μM for 2 min following permeabilization; the Ca21 EC50 was 2.29 6 0.07 μM. Permeabilized SPOC1 cells were exposed to PMA or 4a-phorbol at Ca21 activities ranging from 10 nM to 10 μM. PMA, but not 4a-phorbol, increased mucin release at all Ca21 activities tested: at 10 nM Ca21 mucin release was 2.1-fold greater than control and at 4.7 μM Ca21 mucin release was maximal (3.6-fold increase). PMA stimulated 27% more mucin release at 4.7 μM than at 10 nM Ca21. Hence, SPOC1 cells possess Ca21-insensitive, PKC-dependent, and Ca21-dependent PKCpotentiated pathways for mucin granule exocytosis.