C-TYPE NATRIURETIC PEPTIDE INCREASES CHLORIDE PERMEABILITY IN NORMAL AND CYSTIC-FIBROSIS AIRWAY CELLS

C-type natriuretic peptide (CNP), a hormone which stimulates particula te guanylate cyclase activity, was studied for its ability to stimulat e chloride permeability through the cystic fibrosis transmembrane cond uctance regulator (CFTR) in airway epithelial cells. Two cell lines, C alu-3 and CF-T43, were used as models of normal and cystic fibrosis (C F) airway epithelial cells, respectively. Calu-3 cells, derived from a lung carcinoma, express relatively high levels of wild-type CFTR. CF- T43 is a transformed line derived from a nasal polyp and expresses the mutant CFTR, Delta F508. Calu-3 cells exposed to the nucleotide guano sine-3',5'-monophosphate (cGMP) analogue 8-Br-cGMP exhibit increased C l-36(-) efflux, demonstrating that cGMP can mediate changes in chlorid e permeability. CNP induces a bumetanide-sensitive short circuit curre nt across Calu-3 monolayers. Whole-cell currents stimulated by CNP dis play linear current-voltage relationships and have inhibitor pharmacol ogy and ion selectivity consistent with CFTR channel activity. Sodium nitroprusside (SNP), an activator of soluble guanylate cyclase, and CN P both increase cGMP levels and short circuit current in Calu-3 cells. In contrast, expsoure of CF-T43 cells to CNP resulted in an increased Cl-36(-) efflux rate only when combined with the adenylate cyclase ag onist isoproterenol and the response was sensitive to kinase inhibitor s. CF-T43 cells exposed to isoproterenol and SNP showed no increase in chloride efflux. Together, these data indicate that CNP can activate wild-type and mutant CFTR through a cAMP-dependent protein kinase path way and that the sensitivity of Calu-3 cells for this stimulation is g reater than that of the CF-T43 cells.