Control of electrogenic Na+ absorption in rat late distal colon by nanomolar aldosterone added in vitro.
It has been possible to obtain in a mammalian epithelium of dietetically and surgically untreated animals a dose response of in vitro-added aldosterone (Aldo, 10(-10) to 10(-5) M) on electrogenic Na+ absorption (JeNa). JeNa was measured in the Ussing chamber on stripped rat late distal colon 8 h after in vitro addition of Aldo. Submaximal effects were obtained at 3 nM Aldo; after a lag time of 2 h, short-circuit current (Isc) increased to a maximum of 234 +/- 15 microA/cm2 and dropped after 0.1 mM amiloride to -18 +/- 3 microA/cm2, resulting in JeNa of 9.4 +/- 0.6 mumol.h-1 x cm-1. Net Na+ tracer fluxes and Isc exhibited parallel time courses, so that electroneutral Na+ transport was not induced in late distal colon by acute Aldo. A plot of JeNa vs. Na conductance revealed an electromotive force (ENa) of 126 +/- 1 mV for all Aldo concentrations tested. Kinetic data were as follows: Michaelis constant 1.2 nM, maximal velocity (Vmax) 10.5 mumol.h-1 x cm-2, and Hill coefficient 2.1. In contrast to the large effect in late distal colon, 3 nM Aldo caused JeNa of < 1 mumol.h-1 x cm-2 in early distal colon, proximal colon, and cecum. Antimineralocorticoid sensitivity and ENa did not vary with Aldo concentration or time of the experiment, consistent with a unique mechanism during the early and late response up to 8 h, as well as at mineralocorticoid and glucocorticoid Aldo concentrations. Acute Aldo in a range of 0.1-10 nM fully controls JeNa between zero and Vmax in late distal colon.(ABSTRACT TRUNCATED AT 250 WORDS)
Fromm
M
M
Institut für Klinische Physiologie, Freie Universität Berlin, Germany.
Schulzke
J D
JD
Hegel
U
U
D000450:Aldosterone / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport; D003106:Colon / Q000378:metabolism* / Q000502:physiology; D004594:Electrophysiology; D066298:In Vitro Techniques; D007408:Intestinal Absorption; D008297:Male; D009994:Osmolar Concentration; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism*; D013997:Time Factors
D000450:Aldosterone; D012964:Sodium