AJP - Cell Physiology, Vol 262, Issue 4 C899-C906, Copyright © 1992 by American Physiological Society
Sodium-independent effect of aldosterone on initial rate of ouabain binding in A6 cells
A. M. Pellanda, H. P. Gaeggeler, J. D. Horisberger and B. C. Rossier
Institut de Pharmacologie de l'Universite Lausanne, Switzerland.
To estimate the early effect of aldosterone on the number of active
Na(+)-K+ pumps at the basolateral membrane of amphibian tight epithelia, we
have measured the initial rate (at 4 min) of [3H]ouabain binding to the
basolateral membrane of intact monolayers of A6 cells grown on permeable
supports. Within 3 h, aldosterone induced a threefold increase of the Na
transport and, simultaneously, a twofold increase of the binding rate of
ouabain. Because the affinity of ouabain, estimated either by equilibrium
binding studies or inhibition kinetics, was not modified by aldosterone,
the effect on the initial rate of ouabain binding was due to an increase in
the number of binding sites. This effect on ouabain binding was not
prevented by 10 microM amiloride, which reduced the transepithelial sodium
transport below control level. By contrast, the effect of aldosterone on
ouabain binding was abolished by cycloheximide (5 micrograms/ml) or
actinomycin D (2 micrograms/ml), doses which inhibited the
aldosterone-dependent sodium transport response. These data suggest that
aldosterone elicits an early, sodium-independent, protein
synthesis-dependent increase in the expression of active Na(+)-K(+)-ATPase
molecules.
