AJP - Gastrointestinal and Liver Physiology, Vol 241, Issue 2 104-G108, Copyright © 1981 by American Physiological Society
Ouabain binding to isolated frog gastric mucosa
V. M. France and R. P. Durbin
Inhibition of gastric acid secretion by the cardiac glycoside, ouabain, is
considerably reduced by elevating external K+ as first shown by Davenport
(Proc. Soc. Exp. Biol. Med. 110: 613-615, 1962). To determine the possible
role of K+ in this effect, we measured [3H]ouabain binding in isolated
bullfrog gastric mucosa. Uptake of the labeled drug showed two components:
one that saturated at 0.36 pmol ouabain per milligram wet weight and one
that was linear with the external ouabain concentration. The former
component is considered to represent specific binding to Na+-K+-ATPase;
activity of this enzyme system in mucosal homogenates was 0.2 mumol per
milligram protein per hour. Increase of K+ in the nutrient bathing solution
from 3 to 30 mM, or replacement of Na+ by K+ in the secretory bathing
solution, largely reversed inhibition of acid secretion by ouabain but did
not affect maximum specific binding. The results fit a model in which
Na+-K+-ATPase is normally required in oxyntic cells to maintain a high K+
level, which in turn supports exchange of K+ for H+ at the apical surface.
