Defective regulation of gap junctional coupling in cystic fibrosis pancreatic duct cells

The cystic fibrosis (CF) gene encodes a cAMP-gated Cl- channel (cystic fibr osis transmembrane conductance regulator [CFTR]) that mediates fluid transp ort across the luminal surfaces of a variety of epithelial cells. We have p reviously shown that gap junctional communication and Cl- secretion were co ncurrently regulated by cAMP in cells expressing CFTR. To determine whether intercellular communication and CFTR-dependent secretion are related, we h ave compared gap junctional coupling in a human pancreatic cell line harbor ing the Delta F508 mutation in CFTR and in the same cell line in which the defect was corrected by transfection with wild-type CFTR. Both cell lines e xpressed connexin45 (Cx45), as evidenced by RT-PCR, immunocytochemistry, an d dual patch-clamp recording. Exposure to agents that elevate intracellular cAMP or specifically activate protein kinase A evoked Cl- currents and mar kedly increased junctional conductance of CFTR-expressing pairs, but not in the parental cells. The latter effect, which was caused by an increase in single-channel activity but not in unitary conductance of Cx45 channels, wa s not prevented by exposing CFTR-expressing cells to a Cl- channel blocker. We conclude that expression of functional CFTR restored the cAMP-dependent regulation of junctional conductance in CF cells. Direct intercellular com munication coordinates multicellular activity in tissues that are major tar gets of CF manifestations. Consequently, defective regulation of gap juncti on channels may contribute to the altered functions of tissues affected in CF.