EXPRESSION OF CFTR CONTROLS CAMP-DEPENDENT ACTIVATION OF EPITHELIAL K+ CURRENTS

The perforated-patch configuration of the patch-clamp technique was us ed to record whole cell currents from human epithelial CFPAC-1 cells d efective for functional cystic fibrosis transmembrane conductance regu lator(CFTR). In CFPAC-1 cells, adenosine 3',5'-cyclic monophosphate (c AMP) stimulation with forskolin (10 mu M) plus 8-(4-chlorophenylthio)a denosine 3',5'-cyclic monophosphate (400 mu M) activated neither Cl- n or K+ currents. In the same cells transfected with wild-type CFTR gene , cAMP stimulation produced activation of both Cl- and K+ currents. In Cl--depleted medium (gluconate as a substitute), cAMP stimulation evo ked a K+ current in CFTR-transfected but not in untransfected CFPAC-1 cells. This cAMP-evoked K+ current was the sum of two components: 1) a time-independent inwardly rectifying component, and 2) a slowly relax ing component activated at positive voltages. Increasing intracellular Ca2+ with ionomycin (1 mu M) activated K+ currents in either transfec ted or untransfected cells. In transfected cells, blocking the CFTR co nductance with high-concentration glibenclamide (100 mu M) reduced the K+ current when activated by cAMP but not when activated by Ca2+. Pre treating CFTR-transfected cells for 48 h with interferon-gamma downreg ulated CFTR gene expression and reduced cAMP but not Ca2+ activation o f the whole cell K+ current. From these results, we conclude that func tional membrane CFTR protein influences activation by cAMP of epitheli al K+ currents.