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Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, CCS Bloco G, 21949-900 Rio de Janeiro, Brazil
¹ Department of Medicine-Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
² Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA

(Requests for offprints should be addressed to M M Morales; Email: mmorales{at}biof.ufrj.br)

The cystic fibrosis transmembrane conductance regulator (CFTR) is one of the most intensively investigated Cl^– channels. Different mutations in the CFTR gene cause the disease cystic fibrosis (CF). CFTR is expressed in the apical membrane of various epithelial cells including the intestine. The major organ affected in CF patients is the lung, but it also causes an important dysfunction of intestinal ion transport. The modulation of CFTR mRNA expression by atrial natriuretic peptide (ANP) was investigated in rat proximal colon and in human intestinal CaCo-2 cells by RNase protection assay and semi-quantitative reverse transcriptase PCR techniques. Groups of rats subjected to volume expansion or intravenous infusion of synthetic ANP showed respective increases of 60 and 50% of CFTR mRNA expression in proximal colon. CFTR mRNA was also increased in cells treated with ANP, reaching a maximum effect at 10^–9 M ANP, probably via cGMP. ANP at 10^–9 M was also able to stimulate both the CFTR promoter region (by luciferase assay) and protein expression in CaCo-2 cells (by Western blot and immunoprecipitation/phosphorylation). These results suggested the involvement of ANP, a hormone involved with extracellular volume, in the expression of CFTR in rat proximal colon and CaCo-2 intestinal cells.