Parietal cells contain most of the myosin, filamin and actin present in rat gastric glands.

The association of myosin and a filamin-like protein to the F-actin cytoskeleton of parietal cells was studied in the rat gastric mucosa. Myosin and the filamin-like protein were localized by indirect immunofluorescence microscopy while the distribution of actin was established by using FITC-phalloidin. These cytoskeletal proteins, concentrated in the parietal cells, changed their distribution in correlation with the hydrochloric acid (HCl) secretory state of the cells and the appearance of a developed intracellular canaliculus. Thus, in resting parietal cells, actin showed a patchy distribution, delimiting the poorly developed secretory canaliculi, while myosin and the filamin-like protein distributed diffusely over the cytoplasm. In secreting cells, F-actin was concentrated in the cytoplasmic projections filling the canalicular lumen, while myosin and the filamin-like protein were excluded from this region, concentrating in the adjoining cytoplasm. The present results show that myosin and the filamin-like protein change their association with the secretory membranes in relation to the development of the secretory canaliculus of parietal cells. In resting cells, both proteins associate with the endocellular secretory membranes. In secreting cells, the microvillar projections of the canalicular surface formed by these membranes bind F-actin, but exclude myosin and the filamin-like protein.