Influence of amytal and menadione on high-energy phosphates and acid secretion in frog gastric mucosa

Measurement of ATP and creatine phosphate in isolated frog gastric mucosa showed that amytal depressed the level of both high-energy compounds and inhibited acid secretion. Addition of menadione restored the ATP level to control values and partially restored the creatine phosphate levels but did not support acid secretion. Menadione was found to support that portion of active chloride transport which is not associated with acid output. It is concluded that an amytal-sensitive reaction, presumably mitochondrial coupling site I, is required for acid secretion to occur and that ATP is not a sufficient source of energy for this secretory process.     

Integration of biochemical functions of different cells of RAT gastric mucosa for hydrochloric acid secretion

Summary The regulation patterns of gastric acid secretion in rats were investigated. Pentagastrin and histamine stimulate gastric acid secretion, but the inhibitors of DNA-dependent synthesis of RNA and of proteins prevent only the pentagastrin action. It has been found that pentagastrin induces histidine decarboxylase in gastric mucosa, ensuring local accumulation of histamine. The latter activates adenylate cyclase and results in 3,5-AMP accumulation in gastric tissues. The administration of pentagastrin, histamine or 3,5-AMP enhances the activity of gastric carbonic anhydrase, the enzyme which takes part in HCI formation. The data suggest that these three compounds act sequentially (pentagastrin histamine 3,5-AMP) and the effect of the last one could be mediated through 3,5-AMP dependent protein kinase. The experiments in vitro demonstrated that gastric carbonic anhydrase can be separated into two isoenzymes and the phosphorylation of one of them by the 3,5-AMP dependent protein kinase sharply increases its activity. The findings raise the possibility that histamine and 3,5-AMP, mediating gastrin action, form together with enzymes (histidine decarboxylase, adenylate cyclase, protein kinase, carbonic anhydrase) a cascade of amplifiers.Autoradiographic studies have shown that [³H]-pentagastrin is not bound by oxyntic cells but adheres preferentially to histamine-producing-like endocrine cells and to the chief cells, while³H-histamine adheres preferentially to oxyntic and to chief cells. Electron microscopy indicates that only pentagastrin (but not histamine) initiates in-like endocrine cells ultrastructural changes characteristic for induction. Pentagastrin, histamine and 3,5-AMP administration produces in oxyntic cells ultrastructural changes typical for the secretion processes.These results lead to assumption that pentagastrin (gastrin) induces histidine decarboxylase in-like endocrine cells of gastric glands. Histamine which is secreted enhances adenylate cyclase activity in the neighbouring oxyntic cells where 3,5-AMP dependent protein kinase activates carbonic anhydrase by means of phosphorylation. These different cells form, probably, a multicellular functional unit for gastric acid secretion.An invited article.     

Electromotive chloride transport and gastric acid secretion in the frog

The total active transport of chloride ions across the gastric mucosa can be considered as the sum of two fractions; an acidic one which is equivalent to the acid secreted, and an electromotive one which accounts for the electric energy generated by the gastric mucosa. In the present studies, the relationship between this electromotive chloride transport and acid secretion has been investigated, using specific inhibitors. The rate of electromotive chloride transport was found to be essentially unaffected by changes in the rate of acid secretion, and also by inhibition of acid secretion by thiocyanate. On the other hand, diamox, in combination with histamine, was shown to depress or abolish the gastric electromotive force and to inhibit partially the total chloride transport, while acid was secreted at an almost normal rate. This kind of inhibition is undefined as to its mechanism but seems to be more specific for the gastric chloride transport than any other inhibitor known. It is concluded that acid secretion and electromotive chloride transport involve two different mechanisms, and are not absolutely essential for each other. The present results do not support the view that carbonic anhydrase is essential for acid secretion. They rather suggest an important function of this enzyme in the mechanism of active chloride transport.     

Redox involvement in acid secretion in the amphibian gastric mucosa

Summary Gastric fundic metabolism was studied by spectroscopic observation in frog mucosa during transitions of secretory status in vitro and by direct measurement of pyridine nucleotides and associated metabolites in biopsies of dog fundic mucosa also during secretory oxidation of the redox components from flavin adenine dinucleotide (FAD) to cytochromea ₃. Addition of histamine resulted in reduction of these components with onset of secretion by about 50%. In contrast, the effect of apparently, burimamide and subsequently histamine on the ratio of nicotinamide adenine dinucleotide to nicotinamide adenine dinucleotide, reduced (NAD⁺/NADH) was relatively slight. Further, the presence of burimamide substantially reduces the effect of amytal on the pyridine nucleotide spectrum and abolishes the effect of amytal on FAD and the cytochromes. Measurements of lactate, pyruvate, -ketoglutarate, NH₃ and glutamate in the dog showed that whereas the calculated NAD⁺/NADH ratio in the cytoplasm declined with onset of secretion, the calculated mitochondrial ratio rose. No change was noted in the nicotinamide adenine dinucleotide phosphate/nicotinamide adenine dinucleotide phosphate, reduced (NADP⁺/NADPH) ratio. It is concluded that (1) H₂ antagonists act by blocking substrate flow into the mitochondrial respiratory chain, (2) conversely, histamine stimulation acts at the level of substrate mobilization, and (3) there may be a cross-over in the mitochondrial chain between NAD⁺ and FAD.     

Water flow through frog gastric mucosa

To elucidate the role of protein synthesis in DNA formation, E. coli R2 infected with phage T2 was studed as a model, employing chloramphenicol to inhibit protein synthesis. The following results were obtained. 1. Chloramphenicol inhibited protein synthesis but not synthesis of nucleic acids in uninfected bacteria. 2. Studies of the effect of chloramphenicol on phage maturation indicated a delay of 2 minutes between time of addition and cessation of phage growth. 3. The increase of DNA in phage-infected bacteria was completely suppressed by the addition of chloramphenicol within 2 minutes following infection. Addition at later times showed progressively less inhibitory action depending upon the time interval, and addition after the 10th or 12th minute showed no appreciable effect on DNA synthesis despite the cessation of intracellular phage formation and protein synthesis. 4. When chloramphenicol was added to infected cells the increase of resistance to UV stopped within 2 minutes, whether or not DNA synthesis continued. Thus evolution of resistance paralleled the rate of DNA synthesis achieved, but not the amount of DNA accumulated. 5. We conclude that in infected bacteria, protein synthesis is necessary to initiate DNA synthesis but is not essential for its continuation. The resistance to UV that characterizes infected cells near the midpoint of the latent period is not due to accumulation of DNA, but depends on some chloramphenicol-sensitive process (probably protein synthesis) completed at about the time the rate of DNA synthesis becomes maximal.     

Effect of sterols of cholesterol series on secretion of hydrochloric acid in mucosa of animals

Secretion of hydrochloric acid of frog gastric mucosa in vitro was studied as affected by some sterols of the cholesterol series. This effect is found to depend on both the sterol molecule structure and the substance concentration. 7-dehydrocholesterol and its products of oxidation are supposed to have a specific effect on the process of hydrochloric acid secretion. Possible mechanism of this effect is under discussion.     

Effects of phenothiazines on acid secretion in the toad gastric mucosa

The effect of phenothiazine antipsychotic drugs on acid secretion was investigated in the isolated toad gastric mucosa. The acid secretory responses induced by maximal doses of histamine, carbachol and theophylline were all inhibited in a similar fashion by chlorpromazine. The ID50 was between 300 and 600 microM. Histamine-stimulated H+ secretion was also inhibited by trifluoperazine. Soluble cyclic AMP-dependent protein kinase activity was not significantly affected by 300 microM chlorpromazine. Microsomal (H+ + K+)-ATPase activity was significantly reduced by chlorpromazine. The results indicate that phenothiazines can inhibit acid secretion in the toad gastric mucosa and that inhibition of the gastric (H+ + K+)-ATPase may be involved in the mechanism of action.