Stimulation of cyclic guanosine monophosphate production by natriuretic peptide in human biliary cells

Background and Aims: Guanosine 3',5'-cyclic monophosphate (cGMP), whose production is stimulated by the interaction of nitric oxide, natriuretic peptides, and guanylin with their respective guanylate cyclases, activates secretion through ion channels in several epithelia. Cl^- channels have been identified in the apical membrane of biliary epithelial cells. The aim of this study was to investigate the production of cGMP and its effects on Cl^- permeability in biliary epithelial cells. Methods: Halide efflux measurement, whole-cell patch clamp recording, radioimmunoassay, and reverse- transcription polymerase chain reaction using two human biliary cell lines (H69 and Mz-ChA-1) were performed. Results: In cells equilibrated with ¹²⁵I, bromo-cGMP stimulated halide efflux by 22%. In whole-cell patch clamp recordings, the addition of cGMP intracellularly, or of atrial natriuretic peptide extracellularly, stimulated inward currents at negative membrane potentials, consistent with Cl^- efflux through open channels. In H69 cells, atrial and C-type natriuretic peptides stimulated production of cGMP. Mz-ChA-1 responded only to atrial natriuretic peptide. Both cell lines expressed messenger RNA for the guanylate cyclase type A receptor and the guanylate cyclase free-clearance receptor. Conclusions: These data suggest that natriuretic peptide stimulates cGMP production in human biliary epithelial cells, which in turn may regulate ductular bile formation through the opening of Cl^- channels.