PYRIDINE-NUCLEOTIDE REDOX POTENTIAL MODULATES CYSTIC-FIBROSIS TRANSMEMBRANE CONDUCTANCE REGULATOR CL- CONDUCTANCE

Cl- conductance of the apical membrane of airway epithelial cells has properties of a passive diffusion mechanism but is decreased by inhibi tion of oxidative metabolism. Recent reports that cAMP-dependent Cl- c onductance also requires ATP at the intracellular domains of the cysti c fibrosis transmembrane conductance regulator (CFTR) suggest that ATP concentration could mediate metabolic regulation of Cl- conductance. However, metabolic inhibitors affect processes other than ATP free ene rgy levels, including notably the metabolic pathways that set the redo x potential of pyridine nucleotides within the cell. We have investiga ted the possibility that CFTR-mediated Cl- conductance is affected by the ratio of oxidized to reduced intracellular pyridine nucleotides. C FTR was expressed in airway and heterologous cells and studied under w hole cell. voltage clamp conditions, which permitted the intracellular NAD(P)(+)/ NAD(P)H ratio to be varied independently of ATP concentrat ion. In three cell types expressing CFTR, whole cell dialysis with red uced pyridine nucleotides inhibited activation of Cl- currents by fors kolin and 8-(4-chlorophenylthio)-cAMP (CPT-cAMP), whereas dialysis wit h oxidized pyridines increased both basal and stimulated CFTR-mediated Cl- conductance. In cell-attached membrane patches, the open probabil ity of 5-6-picosiemens Cl- channels that had been activated by forskol in and CPT-cAMP was further and reversibly increased by permeant oxida nts. Neither swelling-induced whole cell K+ currents in CFTR-expressin g cells nor swelling-induced whole cell Cl- currents in multidrug resi stance protein-expressing cells were affected by NADPH. Pyridine nucle otide redox potential had little effect on phosphorylation of histone by protein kinase A. We conclude that CFTR Cl- conductance function ca n be modulated by pyridine nucleotide redox potential. This effect poi nts to the existence of a mechanism or mechanisms by which cytosolic n ucleotides other than ATP can affect plasma membrane Cl- conductance a nd may help explain how a passive ion conductance is linked to cellula r energy metabolism.