Kinetics of cell death induced in 10T1/2 cells by methyl methanesulfonate and the effects of extracellular calcium on cell death.

The cytotoxic effect of methyl methanesulfonate (MMS) on C3H 10T1/2 cells is characterized by a complex pattern of changes in the permeability of the cell membrane to trypan blue and, therefore, presumably to extracellular calcium. 10T1/2 cells are temporarily, and reversibly, permeable to trypan blue during the initial 30 minutes following exposure to MMS when incubated in the presence of extracellular calcium. By 90-120 minutes after the exposure, the MMS treated cells have restored control of the membrane permeability, and for the next 6-7 hours they exhibit a level of trypan blue uptake comparable to that observed in the untreated cohort population. Between 9 and 15 hours after exposure to MMS the fraction of the population permeable to trypan blue increases rapidly, ultimately approximating the level of cell killing measured concurrently in a colony formation assay. Transient culture in calcium-free medium immediately after exposure to MMS does not protect 10T1/2 cells from cytotoxicity, but incubation in the calcium-free medium does prevent the initial transient episode of permeability to trypan blue observed when the 10T1/2 cells are incubated in calcium-containing medium. These observations suggest that MMS-induced cytotoxicity results from a complex course of events, possibly from damage to an intracellular target rather than from damage to the plasma membrane.