Vesicle targeting and ion secretion in epithelial cells : implications for cystic fibrosis

The asymmetric distribution of plasma membrane components is a funda­ mental characteristic of epithelial cells. The elucidation of the cellular mechanisms that establish and maintain spatial asymmetry (cellular polar­ ization) continues to be the major quest of modem epithelial cell biology. The level of research activity and depth of our knowledge in this area is evident from the many detailed reviews published in recent years (17, 60, 87, 103, 130, 142, 143). The ability of an epithelium to secrete or absorb fluid is intimately linked to the asymmetric distribution of ion transport processes within its mem­ branes. The last ten years has seen the wide-spread application of high resolution electrophysiologic recording techniques to epithelial cells, which has led to detailed biophysical descriptions of many of the ion transport proteins involved in the conductive movements of ions across apical and basolateral membranes (31, 47, 145). As a result, epithelial cells have