Ca (2+) -activated C1- channels in a human biliary cell line: regulation by Ca2+/calmodulin-dependent protein kinase
Schlenker, T.; Fitz, J.G.
American Journal of Physiology 271(2 Pt 1): G304-G310
1996
ISSN/ISBN: 0002-9513 PMID: 8770046 Document Number: 464445
Biliary epithelial cells contribute to bile formation through absorption and secretion of fluid and electrolytes. Recent studies indicate that membrane Cl- permeability is regulated in part by increases in intracellular Ca-2+ concentration. The purpose of these studies was to evaluate the effects of intracellular Ca-2+ on channel activity, using the human Mz-ChA-1 cholangiocarcinoma cell line as a model, and to assess the possible roles of Ca-2+-dependent kinases in channel regulation. Exposure to ionomycin (1 mu-M) activated ion channels in the cell-attached configuration in 63 of 74 attempts, increasing open probability (NP-o) from 0 to 0.26 +- 0.15 (n = 17). Multiple channels were present in each patch, and the effects of ionomycin were reversed by subsequent addition of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (2 mM) to the bath. With Cl--containing solutions, channels had a slope conductance of 14 +- 4 pS (n = 11), and the mean open time was estimated to be 5.3 +- 1.8 ms. These channels were anion selective, and currents were carried by efflux of Cl- at the resting potential. Exposure to the Ca-2+/calmodulin-dependent protein kinase II (CaMKII) antagonist calmidazolium (100 mu-M) decreased NP-o in ionomycin-stimulated cells to 0.02 +- 0.06 (n = 19). The protein kinase C antagonist chelerythrine (50 mu-M) was without effect. In parallel studies in subconfluent cell monolayers, CaMKII antagonists were also potent inhibitors of ionomycin-stimulated 125I efflux. These findings indicate that Ca-2+-dependent increases in membrane Cl- permeability are related in part to opening of 14-pS anion channels through a mechanism that depends on both Ca-2+ and CaMKII. These channels represent a potential target for pharmacological modulation of biliary cell transport and function.