beta(3)-adrenoceptor control the cystic fibrosis transmembrane conductanceregulator through a cAMP/protein kinase A-independent pathway

In human cardiac myocytes, we have previously identified a functional beta( 3)-adrenoceptor in which stimulation reduces action potential duration. Sur prisingly, in cardiac biopsies obtained hom cystic fibrosis patients, beta( 3)-adrenoceptor agonists produced no effects on action potential duration. This result suggests the involvement of cystic fibrosis transmembrane condu ctance regulator (CFTR) chloride current in the electrophysiological effect s of beta(3)-adrenoceptor stimulation in non-cystic fibrosis tissues. We th erefore investigated the control of CFTR activity by human beta(3)-adrenoce ptors in a recombinant system: A549 human cells were intranuclearly injecte d with plasmids encoding CFTR and beta(3)-adrenoceptors. CFTR activity was functionally assayed using the 6-methoxy-N-(3-sulfopropyl) quinolinium fluo rescent probe and the patch-clamp technique. injection of CFTR-cDNA alone l ed to the expression of a functional CFTR protein activated by cAMP or cGMP . Co-expression of CFTR (but not of mutated Delta F508-CFTR) with high leve ls of beta(3)-adrenoceptor produced an increased halide permeability under base-line conditions that was not further sensitive to cAMP or beta(3)-adre noceptor stimulation. Patch-clamp experiments confirmed that CFTR channels were permanently activated in cells co-expressing CFTR and a high level of beta(3)-adrenoceptor. Permanent CFTR activation was not associated with ele vated intracellular cAMP or cGMP levels. When the expression level of beta( 3)-adrenoceptor was lowered, CFTR was not activated under base-line conditi ons but became sensitive to beta(3)-adrenoceptor stimulation (isoproterenol plus nadolol, SR 58611, or CGP 12177). This later effect was not prevented by protein kinase A inhibitors. Our results provide molecular evidence tha t CFTR but not mutated Delta F508-CFTR is regulated by beta(3)-adrenoceptor s expression through a protein kinase A-independent pathway.