Immunocytochemical studies of gastric H+,K+-ATPase in the developing rat.

The appearance of the enzyme H+,K+-ATPase was studied in the gastric mucosa of rats during the perinatal period. By means of monoclonal antibodies against the enzyme, immunoreactivity was regularly detected in parietal cells 1 day before birth. The intensity of the staining and the frequency of stained cells increased up to 10-12 days after birth, when adult levels were approached. Electron microscopy showed that the initial staining occurred at the apical surface of the parietal cells, with only faint or no staining at the secretory canaliculi. From 5 days after birth immunoreactivity was observed also at the tubulovesicular membranes.