The overall objectives of this proposal are to study cellular mechanisms underlying secretory function and mucosal resistance to acid-peptic injury. A major focus is to use cell separation techniques to identify the cells producing prostaglandins (PG) in the canine fundic mucosa. PGs will be measured by radioimmunoassay, confirmed by thin layer chromatography. We will verify our recent finding that isolated canine fundic macrophages (CFM) produce large amounts of PGs. Monitoring Factor VIII-related antigen, endothelial cells will be enriched and PG production determined. The regulation of PG formation by fundic macrophages, endothelial cells and mucosal cells will be compared. We will confirm our preliminary finding that CFM produce superoxides in response to phagocytic stimuli, and test the hypothesis that CFM may mediate gastric injury via release of oxygen radicals, lysosomal enzymes, thromboxane and leukotrienes. The mechanisms of secretory cell activation will be studied focusing on the role of cyclic AMP and Ca++. Cytoplasmic [Ca++] will be monitored using Quin2 fluorescence techniques and isotopic flux studies. The role of phosphoinositide turnover in cell activation will be studied in relationship to modulation of cytosolic Ca++ and activation of protein kinase C. The approach will be developed studying chief cells and then applied to parietal and somatostatin cells and, as appropriate, to fundic mast cells and fundic macrophages. Contrasts between activation or inhibition of cell function by various chemotransmitters will provide the critical tool for establishing the specificity and relevance of these cell activation mechanisms. Culture techniques for chief cell monolayers will be refined, focusing on developing conditions (substrates, defined serum-free medium, and conditioned medium) for maintaining differentiation. These monolayers resist a very large H+ gradient and the hypothesis will be tested that specialization of the apical surface underlies barrier function. The resistance of chief cell monolayers to H+ backdiffusion will be studied by electrophysiological and morphological techniques, and differences with nongastric epithelial cells determined. A role for chief cell basolateral membrane acid disposal in cellular resistance to acid-peptic injury will be explored.
