Roles of muscularis mucosae and myofibroblasts in the healing process of acetic acid-induced ulcer.

The changes in the localization of FITC-phalloidin-positive smooth muscle cells and interstitial cells were studied in control and acetic acid-treated rat fundic mucosa. In the control rats, the FITC-phalloidin-positive cells mostly corresponded to the smooth muscle cells of the muscularis mucosae, and the arteriolar and venular smooth muscle cells. On the other hand, 1 week after the acetic acid treatment, the fluorescence of the smooth muscle cells of the muscularis mucosae disappeared and a large number of fluorescent interstitial cells, probably corresponding to myofibroblasts, appeared in the regenerated mucosal layer. Three weeks after the application, severely thickened fluorescent muscularis mucosae were formed and the fluorescence of the interstitial cells was rather decreased.