AJP - Gastrointestinal and Liver Physiology, Vol 244, Issue 3 308-G313, Copyright © 1983 by American Physiological Society
Action of thiocyanate on pH gradient formation by gastric microsomal vesicles
W. W. Reenstra and J. G. Forte
The effects of thiocyanate anion (SCN-) on proton accumulation and ATP
hydrolysis by hog gastric microsomal vesicles have been investigated. The
addition of SCN- to vesicles in the presence of KC1 and valinomycin reduced
ATP-dependent proton accumulation in a dose-dependent manner. Inhibition
was most pronounced in the presence of internal SCN-, which was obtained by
preincubation of vesicles with SCN- or by the addition of K+-valinomycin,
which facilitates entry of SCN-. SCN- does not appear to act by inhibition
of the vesicular H+ pump because 1) there were minimal effects of SCN- on
the rate of ATP hydrolysis, and 2) the initial rate of pH gradient
formation was greater with 20 mM SCN- than with 20 mM Cl-. In the presence
of K+ and valinomycin, external SCN- inhibited ATP-dependent pH gradient
formation by increasing the rate of proton efflux. Preformed pH gradients
(acid interior) were rapidly dissipated by internal, but not external,
SCN-. These results suggest that SCN- acts to increase the rate of passive
proton loss from the vesicle interior and do not support a direct
inhibition of ATP-dependent H+ translocation. The results are consistent
with the formation of the permeant hydrothiocyanic acid within the
vesicles, increasing the rate of proton loss. The data also lend support to
the HSCN backflux hypothesis of Sanders et al. [Am. J. Physiol. 234
(Endocrinol. Metab. Gastrointest. Physiol. 3): E120-E128, 1978] for
inhibition of gastric acid secretion by SCN-.
