Differential effects of trypsin on the epidermis of Rana catesbeiana. Observations on differentiating junctions and cytoskeletons.

The filamentous cytoskeletons of epidermal cells of the bullfrog (Rana catesbeiana) were investigated by electron microscopy. Following treatment with trypsin, sheets of epithelium were removed from swatches of abdominal skin. Trypsinization produces differential effects on the ultrastructure of the various cell layers. The desmosomes of all layers, except those of the stratum corneum, are split by trypsinization and the resulting desmosomal plaques fastened to tonofilaments are retracted into cells to form deep "inpouchings" of the plasma membranes, while tonofilament bundles become diffuse. Epidermal sheets were gently homogenized to form a suspension of cell remnants with damaged plasma membranes as indicated by vital dye exclusion tests and electron microscopy. Cytoskeletons retain their shapes, yet the lateral distances between individual tonofilaments within bundles appear to increase, thus forming diffuse lacelike structures. These observations support the suggestion that tonofilament bundles, when fastened to desmosomes, have elastic properties. The possible role of the cytoskeletons in the maintenance of cell size and shape in an ion-transporting epithelium is discussed.