Purified, hormonally responsive parietal cells from rabbit gastric mucosae were used as a model to study intracellular mechanisms controlling parietal cell HCl secretion. Using a high-resolution, two-dimensional electrophoretic technique, we demonstrate that histamine increases phosphorylation of two parietal cell proteins with approximate molecular weights of 27 and 40 kDa and respective pIs of 5.9 and 6.2. The increase in phosphorylation appears to be mediated via an adenosine 3',5'-cyclic monophosphate (cAMP)-dependent mechanism because cAMP analogues and forskolin stimulate phosphorylation of these proteins, whereas the cholinergic agonist, carbachol, which elevates parietal cell intracellular free calcium concentration but not cAMP content, and the calcium ionophore, ionomycin, do not. Both phosphoproteins are located in low-speed particulate fractions. The 40-kDa phosphoprotein was found in both enriched chief and parietal cells. This phosphoprotein may be cytoskeleton associated, since it is detected in a Triton-insoluble particulate fraction after prolonged exposure of parietal cells to Triton X-100. The 27-kDa phosphoprotein was detected in parietal but not in enriched chief cells and appeared to be localized in a low-speed fraction previously shown to contain increased H+-K+-ATPase activity after histamine stimulation. The location and rapid increase in phosphorylation of the 27-kDa phosphoprotein upon histamine stimulation make this protein an attractive candidate for future studies of intracellular regulation of parietal cell HCl secretion. The 40-kDa phosphoprotein may play a more general role in control of cytoskeletal activity, and perhaps, in morphological transformations associated with stimulus-secretion coupling.
A dynamic and integrated model of gastric HCl secretion: Focus on “Computer modeling of gastric parietal cell: significance of canalicular space, gland lumen, and variable canalicular [K+]”
