cAMP-dependent exocytosis and vesicle traffic regulate CFTR and fluid transport in rat jejunum in vivo.

The cystic fibrosis transmembrane conductance regulator (CFTR) channel is regulated by cAMP-dependent vesicle traffic and exocytosis to the apical membrane in some cell types, but this has not been demonstrated in the intestinal crypt. The distribution of CFTR, lactase (control), and fluid secretion were determined in rat jejunum after cAMP activation in the presence of nocodazole and primaquine to disrupt vesicle traffic. CFTR and lactase were localized by immunofluorescence, and surface proteins were detected by biotinylation of enterocytes. Immunoprecipitates from biotinylated and nonbiotinylated cells were analyzed by streptavidin detection and immunoblots. Immunolocalization confirmed a cAMP-dependent shift of CFTR but not lactase from a subapical compartment to the apical surface associated with fluid secretion that was reduced in the presence of primaquine and nocodazole. Analysis of immunoblots from immunoprecipitates after biotinylation revealed a 3.8 +/- 1.7-fold (P < 0.005) increase of surface-exposed CFTR after vasoactive intestinal peptide (VIP). These measurements provide independent corroboration supporting a role for vesicle traffic in regulating CFTR and cAMP-induced fluid transport in the intestine.