Distribution patterns of cytoplasmic microtubules in epidermal keratinocytes

The distribution of cytoplasmic microtubules in cultured guinea-pig keratinocytes was investigated using immunofluorescence (IF) microscopy with monospecific anti-tubulin antibodies and electron microscopy (EM). In culture, adherent cells displayed networks of thin fluorescent fibres, while a homogeneous and/or granular cytoplasmic IF was shown in the cells of upper layers as well as in trypsinized cells. By EM many microtubules were shown in adherent cells but there were fewer or none in the upper layers. An increase in calcium ion (Ca2+) concentration and the addition of an ionophore (X537A) to the culture medium caused disassembly of microtubules. This effect was cancelled by a calmodulin inhibitor. Cryostat sections of normal human and guinea-pig epidermis stained with anti-tubulin antibodies showed a homogeneous and/or granular cytoplasmic IF from basal to granular layers but no detectable IF was seen in the horny layer. These results suggest that keratinocytes contain a cellular pool of tubulin in various states of polymerization and that microtubule disassembly may occur during differentiation, probably being regulated by Ca2+-calmodulin complexes.