Calcium-activated chloride channels in a human biliary cell line:
regulation by ca2+/calmodulin-dependent protein kinase.
Schlenker, Thorsten, J. Gregory Fitz.
Department of Medicine, Duke University Medical Center, Durham, NC
27710
APStracts 3:0048G, 1996.
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 Ca2+ concentration. Using the human Mz
-ChA-1 cholangiocarcinoma cell line as a model, the purpose of these
studies was to evaluate the effects of intracellular Ca2+ on channel
activity, and to assess the possible roles of Ca2+-dependent kinases
in channel regulation. Exposure to ionomycin (1 [mu]M) activated ion
channels in the cell-attached configuration in 63/74 attempts,
increasing open probability (Po) 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 EGTA (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
Ca2+/calmodulin-dependent protein kinase (CaMKII) antagonist
calmidazolium (100 [mu]M) decreased Po 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 Ca2+-dependent increases in membrane Cl- permeability
are related in part to opening of 14 pS anion channels through a
mechanism which depends upon both Ca2+ and CaMKII. These channels
represent a potential target for pharmacologic modulation of biliary
cell transport and function.
Received 8 August 1995; accepted in final form 15 February 1996.
APS Manuscript Number G340-5.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 March 96