Ontogeny of the rat parietal cell: analysis using anti-parietal cell antibody and transmission electron microscopy.

We studied the ontogeny of the rat parietal cell using human anti-parietal cell antibody and transmission electron microscopy. In the gastric fundus of the rat, we found that the epithelium changed from stratified to columnar at gestational day 18.5. Gastric pits began to form at gestational day 19.5. Primitive fundic glands appeared at gestational day 20.5. Human anti-parietal cell antibody specifically stained the rat parietal cells. By this immunohistochemical staining, rat parietal cells were identified from gestational day 19.5. At first we observed only a few plump parietal cells sparsely located in the fundic glands. In neonatal rats, the parietal cells increased in number and began to distribute themselves over a wider area of the primitive fundic glands especially in the lower half. As the rats grew, the distribution area of the parietal cells expanded to cover the whole of the glands except for the foveolar region. Parietal cells in the isthmus and neck regions were round and plump, while those in the basal region were slender and polygonal. We found that throughout the development of the fundic glands there were several ultrastructural changes of the parietal cells. In the late fetal period, parietal cells containing lysosomes and secretory granules were observed, but no tubulovesicles were identified. Development of the tubulovesicles was remarkable until one week after birth. The ultrastructure of the parietal cells of the neonate and adult varied, depending on their distribution area. We found that parietal cells in the basal region of the fundic glands which are fully matured cells had wider intracellular secretory canaliculi, while cells in the upper region had narrower canaliculi; this indicates the functional difference between hydrochloric acid secretion in parietal cells of the two regions.