GASTRIC PARIETAL-CELL DEVELOPMENT - EXPRESSION OF THE H+ K+ ATPASE SUBUNITS COINCIDES WITH THE BIOGENESIS OF THE SECRETORY MEMBRANES/

The early development of the parietal cell in the embryonic murine gas tric mucosa was investigated with particular attention paid to the bio genesis of the secretory membranes and the localization of the gastric H/K+ ATPase alpha and beta subunits. Gastric glands were recognized i n the day 18 foetus. However, at this stage in development no parietal cells could be distinguished ultrastructurally in the glands, and no immunoreactivity was detected with monoclonal antibodies to either the alpha or beta subunits of the gastric H/K+ ATPase. In the 19 day embr yo, parietal cells were recognizable morphologically by the presence o f slender microvilli on the apical (lumenal) surface and differentiati ng intracellular canaliculi in the apical cytoplasm. Both subunits of the proton pump were found to be specifically associated with the apic al and canalicular membranes and with the membranes of relatively larg e vesicles distributed in the subapical cytoplasm and the cytoplasm su rrounding t canaliculi. In the parietal cells of the day 1 neonate, th e intracellular canaliculi had extended basally to form the extensive compartments typical of parietal cells in the adult animal. Again, pro files of vesicles showing H/K+ ATPase immunoreactivity were present in the pericanalicular cytoplasm. These results indicate that the intrac ellular canaliculi are formed by expansion of the apical surface and s uggest that the delivery of newly synthesized gastric H/K+ ATPase alph a and beta subunits to the apical plasma membrane is mediated by typic al Golgi transport vesicles. The large immunoreactive vesicles that oc cur in the apical and pericanalicular cytoplasm of the developing cell s may represent artefacts generated by fixation-induced fragmentation of the differentiating canalicular membrane system during preparation.