The effects of diazepam on mitosis and the microtubule cytoskeleton II. Observations on newt epithelial and PtK1 cells

Summary The effects of diazepam (DZP) on mitosis and the microtubule (MT) cytoskeleton were examined using live and fixed PtK₁ and newt (Taricha granulosa) epithelial lung cells. DZP treatment caused rapid shortening of spindle MTs at prometaphase and metaphase, inducing movement of the poles together while chromosome oscillations continued. DZP treatment slowed the rate of anaphase A but did not detectably affect anaphase B, cell cleavage or interphase cells. Our results suggest that DZP inhibits mitosis by affecting prometaphase and metaphase MTs. Its action is not equivalent to that of common anti-MT drugs, since only a small subpopulation of MTs are significantly susceptible. Likewise, its effects are not equivalent to those generated by metabolic inhibitors. The related benzodiazepines, medazepam and oxazepam, induce effects equivalent to those of DZP.