Interactions between oxoglutarate oxidation and acid secretion in isolated rabbit gastric glands

Abstract

SUMMARYThe effects of gastric secretagogues, and other agents that modify H+,K+-ATPase activity and cell calcium concentration, on the rate of oxoglutarate oxidation were investigated in isolated gastric glands. Oxoglutarate was oxidized in a dose-dependent manner by gastric glands, with an apparent Km for oxoglutarate of 3 9 + 0 5 mM. Oxoglutarate progressively inhibited the rate of glucose oxidation. In the presence of 0 5 mM oxoglutarate plus 10 mM glucose, the latter substrate was preferentially oxidized and contributed most to oxygen uptake. With 10 mM oxoglutarate plus 10 mM glucose, the rate of glucose oxidation was greatly inhibited and oxoglutarate oxidation accounted for most of the oxygen consumption. Acid secretion (aminopyrine accumulation) was significantly increased by 0.1 mM histamine in glands oxidizing 10 mM oxoglutarate, although this stimulation was significantly lower than that observed in the presence of 0-5 mM oxoglutarate plus 10 mM glucose. Omeprazole, an inhibitor of the H+,K+-ATPase, significantly reduced the oxidation of oxoglutarate, whereas NH4+, an activator of the enzyme, stimulated the oxidation of a submaximal dose of oxoglutarate. Carbachol at 0.1 mm significantly increased the rate of oxidation of non-saturating concentrations of oxoglutarate. The calcium ionophore ionomycin at 10 /M produced a similar effect. Chelation of intracellular calcium by BAPTA AM caused a significant inhibition of oxoglutarate oxidation. The results provide further evidence that changes in the ATP: ADP ratio resulting from activation of the H+,K+-ATPase, and calcium ions are involved in the mechanisms of activation of oxidative metabolism in the parietal cell.