title: Aldosterone-induced apical Na+ and K+ conductances are located predominantly in surface cells in rat distal colon.
abstract: 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 Na+ and K+ conductances may reflect varying stages of differentiation along the surface cell-crypt cell axis.
authors.affiliation: Epithelial Membrane Research Centre, University of Manchester, Hope Hospital, Salford, United Kingdom.
authors.forename: R B
authors.initials: RB
authors.lastname: Lomax
authors.forename: C M
authors.initials: CM
authors.lastname: McNicholas
authors.forename: M
authors.initials: M
authors.lastname: Lombès
authors.forename: G I
authors.initials: GI
authors.lastname: Sandle
mesh_terms: D000450:Aldosterone / Q000494:pharmacology*; D000818:Animals; D002462:Cell Membrane / Q000502:physiology; D003106:Colon / Q000166:cytology / Q000502:physiology*; D004553:Electric Conductivity; D004594:Electrophysiology; D066298:In Vitro Techniques; D008297:Male; D008839:Microelectrodes; D011188:Potassium / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018161:Receptors, Mineralocorticoid / Q000378:metabolism; D012964:Sodium / Q000502:physiology*
chemical_list: D018161:Receptors, Mineralocorticoid; D000450:Aldosterone; D012964:Sodium; D011188:Potassium