AJP - Gastrointestinal and Liver Physiology, Vol 248, Issue 4 424-G431, Copyright © 1985 by American Physiological Society
Differential effects of corticosteroids on Na+ transport in rat distal colon in vitro
D. Jorkasky, M. Cox and G. M. Feldman
We studied rat distal colon during in vitro incubation with aldosterone and
dexamethasone. Both hormones caused short-circuit current (Isc) to increase
with a latency period of approximately 3 h. At the 7th h of incubation,
control colons had a Isc of 72 +/- 8 microA . cm-2 while tissues incubated
with 10(-5) M aldosterone and 10(-8) M dexamethasone, the respective
maximal stimulatory concentrations, had similarly increased Isc, 211 +/- 21
and 185 +/- 18 microA . cm-2, respectively. The increase in Isc induced by
steroids reflected increased net sodium transport: control, 3.4 +/- 0.8;
aldosterone, 6.7 +/- 0.7 (P less than 0.05); and dexamethasone, 7.5 +/- 1.0
mueq . h-1 . cm-2 (P less than 0.025). Spironolactone inhibited the
response to both steroids, but the molar ratio of antagonist to agonist was
less for aldosterone (approximately 5,000:1) than for dexamethasone
(approximately 50,000:1). Amiloride inhibited a greater fraction of
aldosterone-induced Isc (0.70 +/- 0.07) than that of dexamethasone (0.37
+/- 0.07; P less than 0.025). The latter value was similar to the effect of
amiloride on control tissues (0.35 +/- 0.04). These data provide evidence
that the cellular mechanisms by which aldosterone and dexamethasone induce
Na+ transport are different.
