AJP - Gastrointestinal and Liver Physiology, Vol 239, Issue 5 411-G417, Copyright © 1980 by American Physiological Society
Uptake and incorporation of phosphate by frog gastric mucosa
R. P. Durbin and D. Hanzel
Labeled inorganic phosphate (32Pi) was used to follow uptake and
incorporation of phosphate into high-energy intermediates of isolated
bullfrog gastric mucosa. Dependence of uptake on levels of external Pi
showed both saturable nonsaturable components. Measurements at 25 microM
Pi, a level at which the saturable component was predominant, showed a
strong dependence of Pi uptake on external Na+ and pH. Labeling of
adenosine 5'-triphosphate (ATP) and creatine phosphate was rapid, followed
by labeling of adenosine 5'-diphosphate, probably by way of adenylate
kinase. Both alkaline nutrient pH and the uncoupling agent, dinitrophenol,
reduced labeling of ATP with a concomitant inhibition of acid secretion. A
feasible interpretation is that dinitrophenol acts by diminishing
mitochondrial production of ATP, whereas alkaline pH reduces the
utilization of ATP by the K+-ATPase considered to be responsible for acid
production. The results thus agree with the hypothesis that ATP is the
immediate substrate for secretion: only a part of the tissue ATP is
directly available to the acid-producing mechanism, however.
