Probes of parietal cell function.

The site of acid secretion in the gastric mucosa has been inferred, but never proven. Using differential interference-contrast (Nomarski) microscopy an expansion of intracellular vacuoles was observed in the parietal cells of living rabbit gastric glands following histamine stimulation. A similar vacuolization occurring only in part of a parietal cell population could be induced by high concentrations of accumulated weak base, aminopyrine, in the absence of secretagogue. In high-K+ medium, 10(-3) M aminopyrine induced massive vacuolization in all parietal cells, consistent with the strong effect of high K+ in stimulating aminopyrine uptake by isolated glands. Electron micrographs showed that the apparent vacuoles correspond to the secretory canaliculi in various stages of swelling. Acridine orange, a fluorescent dye which is distributed across natural membranes as a function of a pH gradient and binds in a multimolecular fashion (stacking) to negative sites, was accumulated by gastric glands as a function of acid secretion. Visualization of such glands by fluorescence or a combination of Nomarski and fluorescence microscopy showed a red fluorescence in the expanding secretory canaliculi that was in sharp contrast to the green fluorescence in the rest of the cell. From these data it is concluded that the site of acid secretion is indeed the secretory canaliculus of the parietal cell. It is also possible that the formation of secretory canaliculi may be induced osmotically and that the peripheral "parietal" position and triangular shape of the parietal cell is necessary to allow expansion and oriented apical flow of HCl.