Regulation of mucin secretion in human gallbladder epithelial cells: predominant role of calcium and protein kinase C.

Abstract

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. [1-(14)C]-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. 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-12-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 P2U receptors, cytosolic calcium increase, and PKC and by taurochenodeoxycholate via cytosolic calcium increase and Ca2+/CaM-kinase II. 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.