Morphometrical analysis of ultrastructural transformation in gastric parietal cells reverting from the active to the resting state processed by high‐pressure freezing.

To elucidate a functional transformation of gastric parietal cells, we have newly developed an isolated rat gastric mucosa model whose parietal cells exhibited a reverting process from the active to resting state of acid secretion. Briefly, the parietal cells were treated with H2‐receptor blocker following prior stimulation of acid secretion in the model, and cryofixed by high‐pressure freezing for electron microscopy. As a result, immunohistochemistry of H + /K + ‐ATPase demonstrated a progressive translocation of H + /K + ‐ATPase from the apical to the cytoplasmic region. The ultrastructure of parietal cells at 5 min in the reverting phase was quite similar to that of maximally stimulated one. The apical membranes were subsequently internalized into the cytoplasm forming unique penta‐laminar membranes. Interestingly, at 90 min in the reverting phase, the penta‐laminar membranes formed a number of multilamellar autophagosomes that were intensely labeled for H + /K + ‐ATPase. Then, the parietal cells exhibited well‐developed Golgi apparatus and lysosomal compartments, and mostly reverted to their resting conformation at 120 min in the reverting phase. Morphometrical analysis indicated a remarkable decrease in the apical membrane/tubulovesicular membrane ratio and increase in the number of both lysosomes and multivesicular bodies as the reverting process.