Induction of spindle inhibition and abnormal mitotic figures by Cr(II), Cr(III) and Cr(VI) ions.
A differential staining technique for chromosomes and spindles was used to compare the effects of chromium compounds of different oxidation states with either no, or very low (Cr(II) and Cr(III) or high (Cr(VI) carcinogenic properties. Neither CrCl2, nor CrCl3 (except at 10(-4) M) had any effect on spindle formation and/or chromosome segregation after exposure up to 10(-7) and 10(-5) M, respectively. None of them significantly influenced the mitotic index. In contrast, the Cr(VI) products (Na2CrO4 and CaCrO4) induced a dose-dependent increase of aberrant division patterns up to 10(-4) and 10(-5) M, respectively. Moreover, with CaCrO4, a high frequency of cells with dislocated metaphase chromosomes or malformed spindles with clustered chromosomes were observed. Since these cell types are potential sources of aneuploid daughter cells, they represent a potential risk for cancer induction. These experiments clearly demonstrate that the differential staining methods allows discrimination between spindle modifiers which induce lethal toxicity and those which may lead to possible tumour induction.