Histamine-stimulated Mucosa Research Articles

Ca2+ requirement for metabolic effects of secretagogues in the amphibian gastric mucosa

The role of extracellular Ca2+ in metabolic effects induced by theophylline and histamine was investigated in the isolated toad gastric mucosa. Primary and secondary effects on metabolism were differentiated by using K(+)-free solutions, which blocked the secretory responses but not the metabolic ones. The stimulation of respiration induced by theophylline and histamine was dose dependent and was significantly decreased by Ca2(+)-free solutions. In the presence of 1.8 mM Ca2+, the rate of glycogen breakdown was increased by theophylline in a dose-dependent manner and the dose-response curve was somewhat similar to that obtained with oxygen uptake. This effect was inhibited by incubation in Ca2(+)-free solutions. Ca2+ stimulated the rate of glycogen utilization in a concentration-dependent manner. The rates of oxidation of exogenous glucose and pyruvate were significantly inhibited by Ca2(+)-free solutions in theophylline- and histamine-stimulated mucosa, whereas the rates of oxidation of butyrate and acetate were not significantly affected. The Ca2+ ionophore A23187 significantly stimulated the rate of oxygen uptake and this response was not blocked by omeprazole and Sch 28080, two specific inhibitors of gastric H(+)-K(+)-ATPase. The results indicate that Ca2+ is required for optimal stimulation of carbohydrate catabolism in the toad gastric mucosa.

Potassium selectivity of frog gastric luminal membrane

Transmural potential difference (PD) and resistance (R) changes after luminal or serosal instillation of K+ were determined under various conditions in chambered preparations of frog gastric mucosae. Potassium selectivity of the luminal membrane is indicated by the rapid reversal of the inverted PD of mucosae bathed in NaCl-free, choline sulfate (Ch2SO4)-Ringer on the serosal side and unbuffered hypertonic Ch2SO4 solution on the luminal side on luminal K+ instillation. The delta PD responses are significantly attenuated, however, in histamine-stimulated mucosae bathed in hypotonic or in burimamide-inhibited mucosae bathed in hyper- and hypotonic luminal media, which suggests that the K+ selectivity of the luminal membrane resides largely in the tubular cell apical membrane. Imposing a serosal-to-luminal transmucosal K+ gradient in both histamine-stimulated and omeprazole-inhibited mucosae also reversed the normal orientation of PD but not in those inhibited with burimamide. In the latter, the PD inversion was attenuated but maintained its normal orientation. These data suggest that burimamide, but not omeprazole, acts by blocking luminal membrane K+ conductance. The inverted PD in mucosae bathed in Cl-free media may thus be due partially or fully to K+ diffusion driven by the cell-to-lumen K+ gradient via the luminal K+ conductance pathway. These findings have implications for the controversy surrounding the postulated electrogenicity of the gastric proton pump.

Secretion of H+ and K+ by bullfrog gastric mucosa: characterization of K+ transport pathway.

The transport of K+ and H+ (both expressed as mueq/h) by in vitro chambered bullfrog (Rana catesbeiana) gastric mucosa have been studied under a variety of conditions such as anoxia, addition of p-chloromercuribenzene sulfonic acid (PCMBS) into the secretory solution, inclusion of ouabain in the nutrient solution, addition of thiocyanate (SCN-) into the mucosal solution, and replacement of nutrient chloride (Cl-) with sulfate (SO4(2-)), or gluconate (Gl). Anoxia reversibly reduced the H+ transport close to zero within 15 min and gradually reduces the K+ transport throughout the 2-h period of anoxia. The presence of 2.5 X 10(-4) M mucosal PCMBS in the histamine-stimulated mucosa increases the K+ transport, which is promptly reduced by changing the gas phase to 95% N2-5% CO2. Addition of ouabain to the nutrient solution of the histamine-stimulated mucosa with PCMBS on the mucosal side significantly (P < 0.05) reduces the K+ transport within 60 min. Addition of SCN- to the mucosal solution of a histamine-stimulated mucosa with regular nutrient or O, K+ nutrient and 10, K+ mucosal solution reduces the H+ transport to near zero within 60 min. This SCN- inhibition can be reversed by elevating secretory K+. Substitution of nutrient Cl- with SO4(2-) or Gl in the histamine-stimulated mucosa reversibly inhibits H+ transport and reduces K+ transport to a low level (0.7 +/- 0.05). Our data suggest that the K+ transport across the apical membranes of gastric cells is to a large extent a passive carrier-mediated process, and the transport of both K+ and Cl- are coupled at the apical membrane.

Histamine-stimulated hydrogen ion secretion by in vitro piglet gastric mucosa.

1. A new preparation of gastric mucosa isolated from new-born piglets is described. The piglet gastric mucosa was easily separated from the serosal muscle layers by a "blistering" technique which appeared to cause minimal trauma to the tissue and which allowed extended study in vitro in a suitable chamber. Normal resting p.d. was approximately minus 30 mV (mucosal side negative with respect to serosal side), resistance about 100 omega. cm-2 and H+ secretion was absent or occurred at very low rates (0-1mu-equiv/cm-2. hr). 2. Maximally stimulating doses of histamine (1-6 times 10-5 M) caused H+ secretion to increase (up to 15 muequiv/cm-2. hr), p.d. to increase and resistance to decrease. A close correlation was observed between the increase in H+ secretion and decrease in transmucosal resistance. The threshold dose of histamine appeared to be 10-8 M; concentrations 10-4 M and higher reduced H+ secretion somewhat. 3. Pentagastrin ( 10-9-10-7 M) and acetylcholine (10-7-10-5 M) did not significantly stimulate the piglet gastric mucosa. Pentagastrin concentrations above 4 times 10-6 M reversibly inhibited H+ secretion of histamine-stimulated mucosa. High concentrations of acetylcholine (above 4 times 10-4 M) did not affect histamine-stimulated H+ secretion, but a significant reduction in p.d. was observed. 4. This investigation demonstrates the utility of the piglet gastric mucosa for in vitro studies of the mechanism H+ secretion and the action of secretagogues. From a consideration of such factors as the thinness of tissue and ease of preparation it is suggested that neonatal animals may represent a good source of in vitro mammalian gastric tissue.

Active transport and ATP in frog gastric mucosa

Measurement of adenine nucleotides in isolated frog gastric mucosae showed that ADP levels were elevated by stimulating acid secretion in resting preparations. The ratio, ATP/ADP, was thereby decreased upon stimulation. These changes could be prevented by blocking acid secretion, using Cl-free solutions to bathe the mucosa. Treatment of histamine-stimulated mucosae with ouabain, K-free solutions or acetazolamide significantly depressed acid secretion and increased ATP/ADP. These results are consistent with the hypothesis that ATP is the immediate substrate for acid secretion and they suggest that secretagogues act by increasing ATP utilization.

Phospholipid turnover and ultrastructural changes in resting and secreting bullfrog gastric mucosa

1. 1. Ultrastructural changes and 32P 1 incorporation into phospholipids were studied in resting and histamine-stimulated bullfrog gastric mucosae. 2. 2. The relatively smooth apical surface of the resting oxyntic cell becomes engrossed with elaborate microvilli with the onset of acid secretion induced by histamine. These membranous alterations occur presumably at the expense of the abundant smooth endoplasmic reticulum present in the oxyntic cells. Our observations thus confirm the previous findings of other investigators. 3. 3. The ultrastructural changes were accompanied by an increase in the incorporation of 32P 1 into the phospholipid fraction of the histamine-stimulated mucosae, but did not involve a significant net synthesis of lipids. 4. 4. There was a 2–5-fold enhanced incorporation of 32P 1 into phosphatidyl choline and phosphatidyl ethanolamine, and a smaller change in incorporation into phosphatidic acid and phosphatidyl inositol in the mucosae stimulated by histamine. Phosphatidyl serine and sphingomyelin showed relatively little 32P 1 incorporation. 5. 5. Thiocyanate, an inhibitor of acid secretion, abolished the enhanced 32P 1 incorporation into the specific phospholipids. 6. 6. Changes in 32P 1 incorporation into ATP and acid-soluble phosphate ester fraction of the stimulated mucosae were variable. However, even the greatest change observed was not sufficient to account for the large changes observed in specific phospholipids. 7. 7. [2- 14C]Acetate was incorporated to varying degrees into different phospholipids; the greatest incorporation occurred in phosphatidyl choline. However, histamine stimulation did not significantly alter the incorporation of 14C into any of the phospholipids. 8. 8. The increased turnover of the polar groups of phospholipids thus appears to be correlated with alterations and movements of membranous structures concomitant with the histamine-induced acid secretion in gastric mucosa.

Action of histamine on the permeability of the frog gastric mucosa to potassium and water

The permeability to potassium and water of the isolated gastric mucosa of the frog, Rana pipiens, has been studied. Measurements were realized in spontaneously secreting and histamine (2·10 −5 M) stimulated mucosae in vitro. Electrical potential differences and net potassium fluxes were measured in solutions containing known potassium concentrations. Permeability coefficients for potassium of 11.8·10 −6 and 22.6·10 −6 cm/sec were calculated for the spontaneously secreting and histamine-stimulated mucosae, respectively. A diffusion permeability coefficient for water of 0.42·10 −4 ml/cm 2·sec, was obtained for the spontaneously secreting mucosa using 3H-labelled water; addition of histamine did not change the water diffusion rate. Values of 2.2·10 −2 and 3.7·10 −2 cm 4/sec per mole of glucose were obtained for the permeability coefficient for water filtration in the spontaneously secreting and histamine-stimulated mucosae, respectively. From these findings, it may be concluded (a) that stimulation with histamine increases the permeability of the mucosa to potassium and to water filtration, and (b) that the main barrier for the diffusion of water and that for filtration of water are different, the one for diffusion being insensitive to histamine at the concentration used.