SUBCELLULAR-LOCALIZATION OF CFTR TO ENDOSOMES IN A DUCTAL EPITHELIUM

Plasma membrane chloride transport by the cystic fibrosis transmembran e conductance regulator (CFTR) may be regulated by cellular processes that affect the cycling of CFTR with the plasma membrane. Testing this hypothesis requires cytochemical evidence for the presence of a subce llular compartment of CFTR. In this study, the subcellular distributio n of CFTR in a normal epithelial cell population was characterized usi ng immunofluorescence and immunoelectron microscopy. Two anti-CFTR ant ibodies, raised against different epitopes of the CFTR molecule, speci fically labeled the apical pole of striated duct epithelial cells in t issue sections of rat submandibular gland. By use of electron microsco py, the CFTR immunoreactivity was associated with the apical plasma me mbrane and the membranes of many subapical vesicles. In this preparati on, some of the CFTR-labeled vesicles were also labeled with antibodie s against transferrin receptor and rab4, two markers of early endosome s and receptor-mediated endocytosis. These observations provide direct cytochemical evidence for the existence of peripherally located CFTR- expressing endosomes and support the hypothesis that membrane recyclin g may contribute to CFTR function.