The cystic fibrosis gene product, CFTR, is a Cl- channel that possesses specific binding sites for cytosolic ATP and is activated by cAMP-dependent protein kinase. Most recently, it was reported that CFTR localizes at the surface apical compartment of normal airway epithelial cells, but accumulates in the cytosol of airway cells from CF patients with the delta F508 mutation. In order to explore whether the same difference exists in normal and CF established cell lines that are commonly used in physiological and pharmacological investigations of the CF defect, we employed monoclonal antibodies raised against synthetic peptides corresponding to two different regions of the CFTR protein. One antibody (MATG 1061) was generated against amino acids 503-515 delta 508 in the nucleotide binding domain 1, whereas the other (MATG 1031) was generated against amino acids 107-117 situated in a putative external loop. We used confocal laser scanning microscopy to localize the CFTR protein in T84 (a colonic derived carcinoma), CAPAN-1 (a pancreatic carcinoma), and in CFPAC-1 (a pancreatic carcinoma homozygous for the delta F508 deletion) cell lines. In permeabilized T84 and CAPAN-1 cells, immunolabeling with MATG 1061 predominated at the apical domain. By contrast, CFTR staining with MATG 1061 was homogeneously distributed in the cytoplasm of CFPAC-1 cells. In non-permeabilized non-CF cell lines, MATG 1031 specifically labeled an apical membrane surface epitope. No such labeling was present in CFPAC-1 cells.(ABSTRACT TRUNCATED AT 250 WORDS)