Change in subcellular localization of gastrin-like immunoreactivity in epithelial cells of rat duodenum induced by carbachol.

The present study provides morphological evidence to support the contention of exocrine secretion from duodenal gastrin-containing cells. The isolated vascularly perfused duodenal preparation with or without carbachol stimulation was used. At the end of perfusion, tissue was fixed and prepared for electron microscopic examination. For immunoelectron microscopic study for gastrin, postembedding immunogold reaction combined with preembedding DAB staining was used. In saline-treated controls, DAB reaction was restricted to the basal cytoplasm and immunogold labeling was concentrated over electron-dense cores of secretory granules packed at the basal cytoplasm. However, in carbachol-stimulated animals, immunogold labeling as well as DAB reactions were accumulated at the apical portion of the cytoplasm, suggesting that a high concentration of gastrin was involved in the apical cytoplasm. In carbachol-stimulated cells, aggregation of small vesicles was observed beneath the microvilli, and most of these vesicles had no cores but were similar in size to the basal secretory granules. Immunogold particles were diffusely scattered at the cytoplasm outside these vesicles. These findings suggest that the gastrin-like immunoreactivity was pooled at the matrix of apical cytoplasm in carbachol-stimulated cells, which might be derived from the secretory granules migrated from the basal cytoplasm into apical portion of the cells. In conclusion, the present study demonstrated the change in subcellular localization of gastrin-like immunoreactivity in intestinal gastrin cells after stimulation with carbachol. Aggregation of immunoreactivity at the apical portion of the cells suggests that gastrin may be released into the intestinal lumen.