| Abstract: | Gastric heavy microsomal membranes highly enriched in (H+-K+)-ATPase were obtained from cimetidine- or carbachol-treated rats through 2H2O and Percoll gradient centrifugations. Both the resting (cimetidine-treated) and the stimulated (carbachol-treated) heavy membranes which presumably represent the apical membrane of gastric parietal cells were enriched with the polypeptides of 81,000 and 45,000 besides that of 93,000 representing (H+-K+)-ATPase. No apparent differences could be detected between the resting and the stimulated heavy membranes in their polypeptide profiles or their specific activity of (H+-K+)-ATPase. Nevertheless, the level of 86RbCl uptake was greater in the stimulated than the resting heavy microsomal membrane vesicles. The light gastric microsomes which abound in intracellular tubulovesicles containing reserve (H+-K+)-ATPase as isolated from cimetidine-treated rats were similarly purified with respect to (H+-K+)-ATPase. The purified light gastric membranes were largely devoid of the polypeptides of 81,000 and 45,000 found in the heavy gastric membranes. These observations further support the current hypothesis that secretagogues bring about changes in the environment of (H+-K+)-ATPase and induce KCl permeability in the apical membrane of the parietal cells, although at present we have been unable to identify the polypeptide(s) responsible for the KCl pathway. |
