cAMP-regulated whole cell chloride currents in pancreatic duct cells

Using the whole cell configuration of the patch-clamp technique, we have identified an adenosine 3',5'-cyclic monophosphate (cAMP)-regulated chloride conductance in pancreatic duct cells. Basal whole cell currents in single isolated cells were very low (approximately 5 pA/pF) but could be stimulated 17-fold by elevation of intracellular cAMP. The cAMP-activated currents exhibited 1) a high chloride selectivity, 2) a near linear current-voltage relationship, 3) time and voltage independence, 4) block by 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) but not by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), and 5) an anion selectivity sequence based on permeability ratios of SCN > NO3 > Br > Cl > I > HCO3 > F > ClO4 > gluconate. Currents in single cells ran down within a few minutes; however, stable chloride currents could be recorded from duct cell clusters in which four or five cells were in electrical communication. We present evidence suggesting that these cAMP-regulated currents are carried by cystic fibrosis transmembrane conductance regulator (CFTR) chloride channels. Physiologically, these CFTR channels act in parallel with chloride-bicarbonate exchangers to facilitate bicarbonate secretion across the apical plasma membrane of the duct cell.