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 gallbladder epithelial cells were used in primary culture. Methods: [1-C-14]glucosamine-labeled glycoproteins secreted in vitro were analyzed and quantified after exposing cells to activators and inhibitors of the main transduction pathways and to potential biologically active secretagogues. Results: Secreted glycoproteins showed characteristics of biliary mucins. Activators of adenosine 3',5'-cyclic monophosphate-dependent pathway as well as secretin and vasoactive intestinal polypeptide did not significantly modify mucin secretion. By contrast, ionomycin and 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-dependent pathway implicating Ca2+/calmodulin-dependent protein kinase II (Ca2+/CaM-kinase II) and by the activation of protein kinase C (PKC), respectively, as ascertained by using inhibitors. Mucin secretion was stimulated 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. Extracellular adenosine 5'-triphosphate and taurochenodeoxycholate may play a role in the regulation of biliary mucin secretion by activating these different signaling pathways.