AJP - Gastrointestinal and Liver Physiology, Vol 251, Issue 2 161-G168, Copyright © 1986 by American Physiological Society
Role of calcium in secretory and metabolic effects of substrates in the gastric mucosa
J. Chacin, P. Cardenas, P. Lobo and O. Subero
The role of extracellular Ca2+ in the effects and oxidation of metabolic
substrates was investigated in the isolated toad gastric mucosa. In the
presence of lipoate, the stimulating effect of 10 mM glucose on spontaneous
acid secretion was significantly reduced by 76% in Ca2+-free solutions. The
inhibition was overcome by addition of 5 mM Ca2+. The increment in
respiration induced by glucose was also blocked in the absence of external
Ca2+. The effect of 10 mM pyruvate on acid secretion was inhibited by 37%
in Ca2+-free solutions. The secretory responses induced by 10 mM butyrate
and 10 mM octanoate were not significantly affected by Ca2+-free solutions.
The rates of oxidation of [14C]-glucose and [14C]pyruvate were
significantly reduced by incubating in Ca2+-free solutions containing 0.1
mM of EGTA. When O2 uptake and glucose oxidation were measured
simultaneously in the same preparation, the increment in the rate of
glucose oxidation accounted for by 43% of the total increase of respiration
observed in the presence of Ca2+. The rates of oxidation of [14C]butyrate
and [14C]acetate were not significantly affected by Ca2+-free solutions.
The rate of oxidation of [14C]glucose exhibited saturation kinetics versus
concentration and was lower in the absence of external Ca2+ under a range
of glucose concentrations. Similar results were observed when the
experiments were performed in the absence of external potassium to block
the acid secretory process. Ca2+ stimulated the rate of glucose oxidation
in a dose-dependent manner. The kinetics of 45Ca2+ efflux and 45Ca2+ uptake
were not significantly affected by glucose and butyrate.(ABSTRACT TRUNCATED
AT 250 WORDS)
