Fig. 2.
Kinetic analysis of MTX accumulation in an erythroblastoid cell line. K562 cells maintained under normal culture conditions were treated with MTX at extracellular concentrations of 10, 100, and 1000 nM for 0, 1, 2, 4, 8, and 24 hours. Cellular levels of MTX and its polyglutamate metabolites (MTX-PGtotal) were determined by liquid chromatography–tandem mass spectrometry and normalized to cellular protein content. MTX-PGtotal, expressed in PA per microgram of protein, is presented as the mean ± S.D. from three independent experimental evaluations. Data were fit by linear regression, and the resulting slopes were expressed as the calculated rate of MTX-PGtotal accumulation under each treatment condition.