CFTR channel insertion to the apical surface in rat duodenal villus epithelial cells is upregulated by VIP in vivo

cAMP activated insertion of the cystic fibrosis transmembrane conductance r egulator (CFTR) channels from endosomes to the apical plasma membrane has b een hypothesized to regulate surface expression and CFTR function although the physiologic relevance of this remains unclear. We previously identified a subpopulation of small intestinal villus epithelial cells or CFTR high e xpressor (CHE) cells possessing very high levels of apical membrane CFTR in association with a prominent subapical vesicular pool of CFTR. We have exa mined the subcellular redistribution of CFTR in duodenal CHE cells in vivo in response to the cAMP activated secretagogue vasoactive intestinal peptid e (VIP), Using anti-CFTR antibodies against the C terminus of rodent CFTR a nd indirect immunofluorescence, we show by quantitative confocal microscopy that CFTR rapidly redistributes from the cytoplasm to the apical surface u pon cAMP stimulation by VIP and returns to the cytoplasm upon removal of VI P stimulation of intracellular cAMP levels. Using ultrastructural and confo cal immunofluorescence examination in the presence or absence of cyclohexim ide, we also show that redistribution was not dependent on new protein synt hesis, changes in endocytosis, or rearrangement of the apical cytoskeleton, These observations suggest that physiologic cAMP activated apical membrane insertion and recycling of CFTR channels in normal CFTR expressing epithel ia contributes to the in vivo regulation of CFTR mediated anion transport.