Figure 6.

Persistent presence of MK-4 was not required for protection. A, Effect of pretreatment with MK-4 on subsequent cystine depletion-induced cell death. OL precursors were preincubated with or without MK-4 (0.1 μm) for 1 hr in cystine-free medium, followed by wash three times with cystine-free medium, when indicated. Cell viability was determined 24 hr later, and the percentage of cell survival was based on the control in which cells were maintained in normal medium. Results are one representative of three independent experiments with similar results. B, Effect of vitamin K treatment at various time intervals after initiation of cystine depletion. Cells were treated with increasing amounts of K₁ or MK-4 (μm) at the time of cystine depletion or the indicated time after cystine depletion. The total cystine deprivation time is 24 hr, and the cell viability was evaluated. l-Cystine (200 μm) was added back to the cystine-free medium at 8 hr after cystine depletion and was used as a control. Results are representative of three experiments.