Uptake and incorporation of phosphate by frog gastric mucosa

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.