The Actions of Secretagogues on Oxygen Uptake by Isolated Mammalian Parietal Cells

Abstract

The action of histamine, carbamylcholine, and gastrin on oxygen uptake by cells isolated from canine fundic mucosa was studied in vitro. Viable mucosal cells were prepared by exposure of separated mucosa sequentially to collagenase and EDTA. Oxygen consumption, determined by polarography, was chosen as an index of physiological response of mucosal cells to secretagogues. Isobutyl methyl xanthine (IMX), carbamylcholine, histamine, and gastrín each independently stimulated oxygen uptake by the unfractionated mucosal cells. The response to histamine was greatly enhanced when IMX was present. In fractions of varying parietal cell content obtained with the Beckman elutriator rotor, basal and stimulated oxygen uptake correlated with the parietal cell content of the fractions. The percentage increases in oxygen uptake in response to histamine, gastrin, carbamylcholine, and IMX were similar in enriched fractions with from 50 to 85% parietal cells and in unenriched starting fractions. The normalized dose-response relations for histamine with an IMX background and for carbamylcholine were also similar in these two fractions. The specificity of these responses was tested by use of an H₂-histamine receptor antagonist, metiamide, and an anticholinergic agent, atropine. At the doses used, neither metiamide (0.1 mM) nor atropine (10 μM) inhibited basal oxygen uptake. Histamine, studied with an IMX background, was inhibited by metiamide but not by atropine, while carbamylcholine was inhibited by atropine but not by metiamide. Neither metiamide nor atropine inhibited gastrin-stimulated oxygen uptake. These data indicate that in this in vitro system parietal cells account for most of the increase in oxygen uptake produced by exposure to gastric secretagogues and that histamine, gastrin, and carbamylcholine each independently stimulate oxygen uptake by the parietal cell. The specificity displayed by atropine and metiamide in this in vitro system suggests that the parietal cell has specific receptors for each of these secretagogues.