ALDOSTERONE-INDUCED APICAL NA+ AND K+ CONDUCTANCES ARE LOCATED PREDOMINANTLY IN SURFACE CELLS IN RAT DISTAL COLON

Aldosterone-induced apical Na+ and K+ conductances are located predominantly in surface cells in rat distal colon. Am. J. Physiol. 266 (Gastrointest. Liver Physiol. 29): G71-G82, 1994.-Aldosterone is a major regulator of Na+-absorptive and K+-secretory processes in the distal segment of mammalian colon. In this study, the distribution of aldosterone-sensitive cell types in isolated rat distal colon was determined using site-directed intracellular microelectrodes, specific Na+- and K+-channel blockers, and aldosterone-receptor binding techniques. Electrophysiological data indicated that aldosterone induced parallel apical membrane Na+ and K+ conductances, mainly in surface cells and to a significantly lesser degree in crypt cells. Scatchard analyses of aldosterone-receptor binding in cytosolic fractions revealed the maximum number of specific binding sites in whole mucosal homogenate and in the upper one-third and lower two-thirds of isolated crypt units to be 74.9+/-2.0, 59.8+/-2.4, and 59.3+/-3.2 fmol/mg protein, respectively, indicating the presence of aldosterone receptors in the crypt cell population. We conclude that in rat distal colon aldosterone-induced Na+ and K+ conductances (and by inference, electrogenic Na+ absorptive and K+-secretory processes) are located predominantly in the surface cell population and to a lesser extent in crypt cells, which also contain aldosterone receptors. This spectrum of aldosterone-induced Naf and Kf conductances may reflect varying stages of differentiation along the surface cell-crypt cell axis.