The principal cell of the kidney collecting duct is one of the most highly regulated epithelial
cell types in vertebrates. The effects of hormonal, autocrine, and paracrine factors to regulate
principal cell transport processes are central to the maintenance of fluid and electrolyte
balance in the face of wide variations in food and water intake. In marked contrast with the
epithelial cells lining the proximal tubule, the collecting duct is electrically tight, and ion and
osmotic gradients can be very high. The central role of principal cells in salt and water …