Localization of carboxyl groups in gastric mucosa as possible sites of gastrin

Summary Human and pig gastrins contain a sequence of five consecutive glutamic acid residues. An attempt was made to localize gastrin using methods known or assumed to operate on a carboxyl mechanism. General methods for acidic groups were combined with selective blocking (methylation) and unblocking (saponification) methods to increase COOH specificity. Epithelial cells with weakly metachromatic granules could be identified in untreated sections stained with toluidine blue (pH 5). After prolonged methylation and saponification, the same and previously obscured cells were moderately to intensely metachromatic, this residual basophilia attributable to weak COOH groups. Specifically marked metachromatic cells were iron-positive after colloidal iron staining, but were delineated easily only after methylation-saponification. Metachromatic cells were also clearly demonstrated by the carboxyl method of Barrnett and Seligman and by silver impregnation (pH 5). The granular metachromatic cell demonstrated by these methods contains significant amounts of a weakly acidic component which the Barrnett-Seligman reaction indicates to be glutamic acid. Comparable staining results were obtained with gastrin producing Zollinger-Ellison islet cell adenomas. It is postulated that the COOH-rich substance is gastrin or gastrin precursor and that the metachromatic cell is responsible for its production.Supported by General Research Support Grant No 5 S01 FR05411-06.