Derangement of microtubule arrays in interphase and mitotic PtK2 cells treated with deuterium oxide (heavy water).

The extent and pattern of the rearrangements of microtubule arrays in interphase and mitotic PtK2 cells treated with deuterium oxide (2H2O) were evaluated using light, immunofluorescence and electron microscopy. Combined labelling with anti-tubulin antibodies and staining with a DNA-specific fluorochrome revealed that 2H2O influences the reassembly of the cytoplasmic microtubule complex (CMTC) of interphase cells after depolymerization of microtubules (MTs) with nocodazole. In cells entering mitosis in the presence of 75% 2H2O the conversion of the CMTC into the mitotic spindle was affected, resulting in a retardation of the prophase/prometaphase transition. (Pro)metaphase cells did not assemble a regular mitotic spindle and the metaphase/anaphase transition was blocked. Immunofluorescence and ultrastructural studies suggest that separation of centrosomes, nucleation of MTs around centrosomes, organization of MTs into the mitotic spindle, as well as the ultrastructure and positioning of the mitotic poles, are affected in deuterated PtK2 cells. In comparison with control cells, a significantly higher proportion of multipolar divisions was found after stimulation of proliferation in the presence of 25-50% 2H2O or during recovery after a long-term exposure to 75% 2H2O. On the basis of these results we discuss the mechanism of the antimitotic action of deuterium oxide and suggest that, apart from perturbation of MT polymerization, it could also encompass disturbances in MT reorganization, most probably by impairment of the microtubule-organizing centres (MTOC).