QUANTITATIVE ULTRASTRUCTURAL-STUDY OF ACRYLAMIDE INDUCED CYTOPLASMIC DESMOSOME-LIKE STRUCTURES IN CULTURED RAT KERATINOCYTES

Although present in many tumours, the mechanism of formation and the s ignificance of the so-called 'cytoplasmic desmosome' (CD) remain specu lative. Recently, we reported an in vitro model for the induction of C D in rat keratinocytes following acrylamide treatment. In the present study and based on quantitative and qualitative evidence, CD could be divided into two categories. The first comprised individually scattere d desmosomes always located in the cortical cytoplasm and associated w ith tonofilament bundles. Their sizes were comparable with those of in tercellular desmosomes (ID) in control cells. The second category comp rised clusters of homogeneously small-size desmosomes that may be loca ted deep in the cytoplasm and were not always associated with tonofila ment bundles. Whilst the latter group may be formed de novo in the cyt oplasm as a result of the acrylamide-induced inhibition of protein kin ases, the first group may be the result of internalization of surface desmosomes by certain tonofilaments under tension. In order to assess this possibility, we examined tonofilament organization following woun ding of the epithelial sheet. Injured cells exhibited spiral-form tono filaments extending close to the cell membrane. This retraction could be justified ultrastructurally by direct association between tonofilam ents and microfilaments.