Expression of stress fibers in bullfrog mesothelial cells in response to tension.

The relationship between stress fibers and tension in mesothelial cells of the bullfrog small intestine was examined by fluorescence cytochemistry using en face mesothelial cell preparations. In nontreated controls, actin revealed by rhodamine-phalloidin staining was localized only along the margins of the mesothelial cells. On the other hand, many stress fibers were formed in the mesothelial cells within 5-7 min after stretching of the intestinal wall in a given direction. The orientation of stress fibers within the cells was coincident with the direction of the tension applied. These cytoplasmic fibers disappeared almost completely from the mesothelial cells within 30 min after the release of tension. According to a difference in the intensity of tension necessary for stress fiber expression, the intestinal mesothelial cells were classified into two groups. Furthermore, cells containing stress fibers in each group showed a rapid increase in number once a given value of tension was applied. The present results indicate that the mesothelial cells of bullfrog small intestine may develop stress fibers to counteract tension exerted on the intestinal wall. Such stress fibers may serve to maintain cellular integrity by strengthening the cellular attachment to subepithelial tissue.