BOVINE PANCREATIC DUCT CELLS EXPRESS CAMP-ACTIVATED AND CA2-ACTIVATEDAPICAL MEMBRANE CL- CONDUCTANCES()

Secretion of salt and water by the epithelial cells that Line pancreat ic ducts depends on activation of apical membrane Cl- conductance. In the present study, we characterized two types of Cl- conductances pres ent in the apical cell membrane of bovine pancreatic duct epithelial c ells. Primary cultures of bovine main pancreatic duct epithelium and a n immortalized cell line (BPD1) derived from primary cultures were use d. Elevation of intracellular adenosine 3',5'-cyclic monophosphate (cA MP) or Ca2+ in intact monolayers of duct epithelium induced sustained anion secretion. Agonist-induced changes in plasma membrane Cl- permea bility were accessed by Cl-36(-) efflux, whole cell current recording, and measurements of transepithelial Cl- current across permeabilized epithelial monolayers. Elevation of intracellular cAMP elicited a sust ained increase in Cl- permeability, whereas elevation of intracellular Ca2+ induced only a transient increase in Cl- permeability. Ca2+ but not cAMP-induced increases in Cl- permeability were abolished by prein cubation of cells with the Ca2+ buffer ,2-bis(2-aminophenoxy)ethane-N, N,N',N'-tetraacetic acid, tetra(acetoxymethyl) ester (BAPTA-AM). N-phe nylanthranilic acid (DPC; 1 mM) and glibenclamide (100 mu M), but not 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; 500 mu M), inh ibited the cAMP-induced increase in Cl- permeability. In contrast, DPC and DIDS, but not glibenclamide, inhibited the Ca2+-induced increase in Cl- permeability. We conclude from these experiments that bovine pa ncreatic duct epithelial cells express at; least two types of Cl- chan nels, cAMP and Ca2+ activated, in the apical cell membrane. Because th e Ca2+-activated increase in Cl- permeability is transient, the extent to which this pathway contributes to sustained anion secretion by the ductal epithelium remains to be determined.