CALLUS AND ITS KERATIN BEFORE AND AFTER TREATMENT WITH ACID SODIUM THIOGLYCOLATE.

The structure of callus differs in many respects from that of normal human stratum corneum. This finding was confirmed both by scanning and transmission electron microscopy. Callous material consists of 2 types of horny cell as does normal stratum corneum. Both types, however, are thicker (5–8 μm) and extremely interdigitated as compared with normal horny cells. All intercellular spaces in callus are occupied by a dense cement material; signs of desquamation are therefore absent. After treatment with acid sodium thioglycolate (aNaThG) the dense matrix of callus keratin is reduced, the keratin framework of the horny cells is loosened and the characteristic α-keratin pattern can be observed. Moreover, most of the intercellular cement material is dissolved and some of the desmosomes are degraded. After aNaThG treatment and prolonged fixation in osmium, only the horny cell borders and a fibrillar skeleton remain. According to our findings, callus keratin is constructed similarly to the keratin of finger pad epidermis and of nail. The mode of keratinization in callus resembles that of hyperkeratosis by proliferation and not parakeratosis. Compared to nail keratin and the keratins of hair, however, callus keratin is less resistant to aNaThG. The high aNaThG-resistance of the horny cell border points to its function as a solid, stable container for keratins. [ABSTRACT FROM AUTHOR]