Mechanism of resistance of Yoshida sarcoma to nitrogen mustard. 3. Mechanism of suppressed transport of nitrogen mustard

Mechanism of decreased transport of nitrogen mustard (HN₂) in HN₂-resistant Yoshida sarcoma cells was investigated. HN₂ uptake by Yoshida sarcoma cells proved to be temperature sensitive, saturable, affected by metabolic inhibitors, and also repressed competitively by choline chloride. In resistant cells, the uptake of choline was markedly depressed. Kinetics of choline transport in resistant cells was comparatively examined, and decreased V_max and increased K_m were observed in some resistant sublines. Accordingly, decrease in choline uptake may be due to decreased activity of choline transport-carrier, both qualitatively and quantitatively. Decreased HN₂ uptake by resistant cells seemed to be produced by the same mechanism.