DEVELOPMENT OF GASTRIC HCL SECRETION

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The general goal of this research is to advance our understanding of the cellular and molecular basis of HCl secretion. The principal pump enzyme responsible for HCl secretion has been identified as the H, K-ATPase. Two very important activities of the H,K-ATPase are fundamental to its participation in gastric secretion; ATP-generated exchange transport of H+ for K+; and stimulation-regulated recycling of H,K-ATPase from a cytoplasmic membrane domain to the apical cell surface. This research will study the gastric pump enzyme, and the accessory elements that contribute to its function and regulation in the secretory cycle. Recent discoveries suggest that the H,K-ATPase is a complex enzyme stabilized as an alpha/beta protomer in the functional membrane, analogous to the closely related Na, K-ATPase. Wee propose that the H,K-ATPase holoenzyme is made up of a 94 kDa catalytic alpha-subunit and a glycoprotein beta-subunit. For one major project of this research specific aims are directed at characterizing the proposed beta-subunit for the H,K-ATPase, and establishing its functional role in the operation and turnover of the pump enzyme. Accordingly, we propose to establish the spatial and temporal concordance of the proposed alpha- and beta-subunits in the putative beta-subunit, including primary amino acid sequence and secondary structure that will be used for functional and theoretical comparisons with other known pump proteins, and detailed oligosaccharide structure as a basis for surface organization and possible protection of parietal cell surfaces. The other major project will exploit the neonatal rabbit stomach model to study genesis and maturation of parietal cells, the H,K-ATPase pumping system, and the signals that control their ontogeny. Specific aims are directed at establishing the origin of cell membrane containing the gastric pump enzyme, the composition and synthetic rates for component peptides (e.g., proposed alpha- and beta-subunits), and post-translational modifications effected during maturation. The nature of accelerated gastric development promoted by glucocorticoid hormones will be defined in terms of location and responsiveness of glucocorticoid receptors, activation of cells and induction of protein synthesis, and the direct or indirect action of glucocorticoid on transcription of the component peptides of the H,K-ATPase.