Filamin and myosin are present in the secretory pole of amphibian oxyntic cells. An immunofluorescence study.

The presence of a filamin-like protein in oxyntic cells was established by indirect immunofluorescence microscopy. The location of this protein and myosin was studied, using specific antibodies, on frozen sections and isolated cells. Antifilamin and antimyosin reacted strongly with the luminal cytoplasm of the cells. In resting oxyntic cells, filamin appeared organized as a reticular sheet in the apical border. In stimulated cells, the apical concentration of filamin decreased, and its distribution appeared rather diffuse. This immunoreactive band seems to correspond to the cytoplasmic region where actin microfilaments have been described previously. The changes in the apical concentration of filamin, induced by the onset of HCl secretion, correlate with the ultrastructural reorganization of the actin network that occurs during the secretory cycle. The use of antimyosin antibodies showed that this protein forms an apical peripheral ring in both resting and stimulated cells. No clear changes in the distribution of myosin, in relation to secretion, could be established by immunofluorescence. These findings, taken together with published morphological and biochemical evidence, suggest that a three-dimensional network composed of actin and filamin is present in the secretory pole of resting amphibian oxyntic cells. The hypothesis that gel-sol transitions play a role in the structural reorganization of the secretory pole of these cells is supported by the present results.