Subcellular distribution of CFTR in rat intestine supports a physiologic role for CFTR regulation by vesicle traffic

The cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP-ac tivated chloride channel critical to intestinal anion secretion. In additio n to phosphorylation, vesicle traffic regulates CFTR in some epithelial cel ls. Studies of cultured intestinal cells are conflicting regarding the role of cAMP-dependent vesicle traffic in regulating chloride transport. Whethe r CFTR is present in vesicular compartments within chloride secretory cells in the intestine is unknown and the role of cAMP-dependent vesicle inserti on in regulating CFTR and intestinal fluid secretion remains unclear. The p urpose of this study was to: (1) examine and quantify the subcellular distr ibution for CFTR in rat intestine, (2) further define the ultrastructure of the previously identified CFTR High Expresser (CHE) cell, and (3) examine the cellular distribution of CFTR following cAMP stimulation in vivo. Using the sensitive techniques of cryoimmunogold electron microscopy we identifi ed CFTR in subapical vesicles and on the apical plasma membrane in crypt, B runner glands, and CHE cells, cAMP stimulation in rat proximal small intest ine produced a fluid secretory response and was associated with an apical r edistribution of CFTR, supporting a physiologic role for cAMP-dependent CFT R vesicle insertion in regulating CFTR in the intestine.