Changes in membrane surface areas in mouse parietal cells in relation to high levels of acid secretion

Levels of gastric acid secretion which may be maximal for the mouse were recorded following treatment with histamine and carbachol. A 30-fold increase over control levels was obtained in perfused animals, corresponding to a fourfold increase over highest levels recorded previously for stimulated mice. Stereological methods were used to estimate surface areas of membrane compartments of parietal cells in control and stimulated animals. Estimates of relative changes in membrane surface areas using a surface ratio method in this case substantiated changes detected by calculating surface densities. Main changes in membrane compartments of parietal cells from animals showing maximal acid secretion were a fourfold increase in free (luminal) surface, a 50% increase approximately in lateral and basal membrane, and a 90% reduction approximately in the tubulovesicular membrane compartment. Following withdrawal of secretagogues, acid secretion usually returned to control levels within 3 hours, but complete reconstitution of the tubulovesicular compartment was not seen within any survival period up to 5 hours. Reappearance of tubulovesicular elements first occurred shortly after the peak of a secretory response in focal cytoplasmic areas containing spherical and indented coated vesicles, and also numerous concentric membrane profiles not previously described in parietal cells. The way in which movement of membrane from the tubulovesicular compartment to the free surface occurs is not yet clear. However, reconstitution of the tubulovesicular compartment during a fall in acid secretion appears to involve movement of membrane from the free surface through coated vesicles, and their progression through indented forms and concentric membrane profiles to vesicles of the tubulovesicular compartment.