HIGH-LEVEL ARSENITE RESISTANCE IN LEISHMANIA-TARENTOLAE IS MEDIATED BY AN ACTIVE EXTRUSION SYSTEM

Leishmania tarentolae cells selected for resistance to the oxyanions p entavalent or trivalent antimonials or to trivalent arsenicals exhibit ed cross-resistance to other oxyanions. The basis for resistance in th ese mutants was studied by transport experiments using radioactive ars enite. All mutants exhibiting high level resistance to arsenite showed a marked decrease in the steady-state accumulation of arsenite. Decre ased accumulation was also observed in antimonials-resistant mutants c ross-resistant to various concentrations of arsenite. Cells depleted o f endogenous energy reserves with metabolic inhibitors were loaded wit h radioactive arsenite; following addition of glucose, rapid efflux of arsenite was observed from arsenite mutant cells. Mutants resistant t o high levels of arsenicals exhibited amplification of P-glycoprotein related gene ltpgpA or of a linear amplicon of unknown function. Howev er, the efflux-mediate arsenite resistance did not correlate with the amplification of the ltpgpA gene or with the presence of the linear am plicon. The calcium channel blocker verapamil and arsenite act in syne rgy in cells exhibiting the efflux system. Overall the oxyanion efflux system in Leishmania shares several properties with other resistance efflux systems mediated by transporters.