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.
Subero
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O
Laboratorio de Investigaciones Gastrointestinales, Facultad de Medicina, Universidad del Zulia, Maracaibo, Venezuela.
Lobo
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Chacín
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J
D000085:Acetates / Q000378:metabolism; D000818:Animals; D000897:Anti-Ulcer Agents / Q000494:pharmacology; D002024:Bufo marinus; D002087:Butyrates / Q000378:metabolism; D020148:Butyric Acid; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D005750:Gastric Juice / Q000187:drug effects / Q000378:metabolism*; D005753:Gastric Mucosa / Q000187:drug effects / Q000378:metabolism*; D006003:Glycogen / Q000378:metabolism; D006632:Histamine / Q000494:pharmacology*; D007093:Imidazoles / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D009853:Omeprazole / Q000494:pharmacology; D010101:Oxygen Consumption / Q000187:drug effects*; D011188:Potassium / Q000494:pharmacology; D013806:Theophylline / Q000494:pharmacology*
D000085:Acetates; D000897:Anti-Ulcer Agents; D002087:Butyrates; D007093:Imidazoles; C035235:Sch 28080; D020148:Butyric Acid; D000001:Calcimycin; D006632:Histamine; D006003:Glycogen; D013806:Theophylline; D009853:Omeprazole; D011188:Potassium; D002118:Calcium