Diurnal variation of methotrexate transport and accumulation in hepatocytes--a consequence of variations in cellular glutathione.
Diurnal variation of the methotrexate (MTX) initial influx and net uptake in isolated rat liver cells was studied in dependence on diurnal variation of cellular glutathione. It was found that the most significant differences concerning the MTX initial transport and accumulation were observed between hepatocytes prepared at 1200 hr when cellular glutathione reached its maximum, and those isolated at 0000 hr when liver glutathione had its minimal concentration. The initial influx of MTX was the biggest in cells isolated at 0000 hr and the smallest in cells prepared at 1200 hr. The Km values in cells with low cellular glutathione (at 1800 and 0000 hr) were about three times smaller than in cells with high glutathione (at 0700 and at 1200 hr), whereas the Vmax value remained unchanged. Titration of external membrane SH groups by [203Hg]p-CMBS revealed a much larger amount of free SH groups on cells having low glutathione level than on those with high glutathione. Despite big initial influx of MTX found in cells with low cellular glutathione, net accumulation of MTX was significantly smaller in these cells as compared with hepatocytes having high glutathione level. In conclusion, the present studies confirmed a statement of the preceding paper on the important role of cellular glutathione played in methotrexate transport and accumulation in rat liver cells.
D000818:Animals; D001692:Biological Transport; D002940:Circadian Rhythm; D005260:Female; D005978:Glutathione / Q000502:physiology*; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008727:Methotrexate / Q000378:metabolism* / Q000633:toxicity; D051381:Rats; D011919:Rats, Inbred Strains
D005978:Glutathione; D008727:Methotrexate