Ion-transport properties of cultured bovine pancreatic duct epithelial cells.

Primary cultures of bovine pancreatic duct epithelial cells grown on permeable supports exhibit electrogenic transepithelial ion transport. The short-circuit current (I(sc)) generated by unstimulated duct cell monolayers and the increase in I(sc) elicited by increased levels of cyclic adenosine monophosphate (cAMP) were greater in monolayers bathed by bicarbonate-containing solution compared with monolayers bathed by nominally bicarbonate-free solution. An inhibitor of epithelial sodium channels (amiloride, 10 microM) had no effect on I(sc), whereas a Cl- channel blocker, N-phenylanthranilic acid (DPC; 1 mM), reduced the forskolin-stimulated I(sc) by approximately 50% in the absence or presence of bicarbonate. Bumetanide (an inhibitor of Na+,K+,2Cl- cotransport activity; 10 microM) reduced forskolin-stimulated I(sc) by 49 +/- 6% in bicarbonate-free bathing solution and by only 18 +/- 1% in bicarbonate-containing solution. Measurements of unidirectional 36Cl- flux across short-circuited ductal monolayers in a bicarbonate-containing solution revealed that net Cl- secretion accounted for the I(sc) during secretin stimulation. However, the basal I(sc) and the I(sc) measured during exposure to secretin plus bumetanide were significantly greater than net Cl- flux. The permeability coefficient for [14C]acetate (a surrogate tracer for bicarbonate) measured in the secretory direction was approximately 1.5-fold greater than the permeability coefficient measured in the absorptive direction, indicating net secretion. These results suggest that primary cultures of bovine pancreatic duct epithelial cells secrete both Cl- and HCO3-.