REGULATION OF MUCIN SECRETION IN HUMAN GALLBLADDER EPITHELIAL-CELLS -PREDOMINANT ROLE OF CALCIUM AND PROTEIN-KINASE-C

Background & Aims: The cellular mechanisms that regulate biliary mucin secretion in humans are unknown. To address this question, human gall bladder epithelial cells were used in primary culture. Methods: [1-C-1 4]glucosamine-labeled glycoproteins secreted in vitro were analyzed an d quantified after exposing cells to activators and inhibitors of the main transduction pathways and to potential biologically active secret agogues. Results: Secreted glycoproteins showed characteristics of bil iary mucins. Activators of adenosine 3',5'-cyclic monophosphate-depend ent pathway as well as secretin and vasoactive intestinal polypeptide did not significantly modify mucin secretion. By contrast, ionomycin a nd phorbol-la-myristate 13-acetate increased mucin secretion by 292% /- 48% and 134% +/- 19% over basal level, respectively. The effects of these two agents were additive and were mediated by a calcium-depende nt pathway implicating Ca2+/calmodulin-dependent protein kinase II (Ca 2+/CaM-kinase II) and by the activation of protein kinase C (PKC), res pectively, as ascertained by using inhibitors. Mucin secretion was sti mulated by extracellular adenosine 5'-triphosphate via P-2U receptors, cytosolic calcium increase, and PKC and by taurochenodeoxycholate via cytosolic calcium increase and Ca2+/CaM-kinase II. Conclusions: Mucin secretion in human gallbladder is regulated predominantly by calcium- dependent pathways implicating Ca2+/CaM-kinase II and PKC. Extracellul ar adenosine 5'-triphosphate and taurochenodeoxycholate may play a rol e in the regulation of biliary mucin secretion by activating these dif ferent signaling pathways.