IMMUNO-CHARACTERIZATION AND FUNCTIONAL-CHARACTERIZATION OF CFTR IN SUBMANDIBULAR AND PANCREATIC ACINAR AND DUCT CELLS

Cystic fibrosis results from defective Cl- channel activity mediated b y the cystic fibrosis transmembrane conductance regulator (CFTR) gene product. In the gastrointestinal tract this is manifested in abnormal salivary secretion and pancreatic insufficiency. This is generally att ributed to defective Cl- transport by the ductal system of the glands. We provide the first immunocytochemical and functional evidence for e xpression of CFTR protein and Cl- current in rat and mouse submandibul ar gland (SMG) and pancreatic acinar cells, a site proximal to the duc tal system of these secretory glands. Monoclonal and polyclonal antibo dies recognizing COOH-terminal epitopes of CFTR show that duct and aci nar cells from the two glands express CFTR in the luminal membrane. Sp ecificity of the polyclonal antibody was verified by absence of staini ng in duct and acinar cells of the SMG of cf(-)/cf(-) and Delta F/Delt a F mice. Identification of CFTR in acinar cells was aided by demonstr ating coexpression of CFTR and type 3 inositol 1,4,5-trisphosphate rec eptors in the luminal pole of acini and absence of type 3 inositol 1,4 ,5-trisphosphate receptors in ducts. Electrophysiological characteriza tion in single SMG duct and acinar cells shows the presence of a prote in kinase A-activated, voltage- and time-independent, ohmic Cl- curren t and absence of repolarization-dependent tail currents, all of which are kinetic properties of the CFTR-dependent Cl- channel. In addition, the channel was activated by the nonhydrolyzable ATP analog 5'-adenyl ylimidodiphosphate and the benzimidazalone NS-004. Channels activated by all activators were inhibited by glibenclamide and a known inhibito ry antiserum [anti-CFTR-(505-511)]. Combined immunologic, functional, and pharmacological evidence allows us to conclude that acinar cells o f the SMG and pancreas express functional CFTR-dependent Cl- channels. Because this site is proximal to the duct, modification of activity o f this channel in acinar cells is likely to contribute to abnormal sal ivary secretion and pancreatic insufficiency typical of cystic fibrosi s.