Increased calcium permeability is not responsible for the rapid lethal effects of amphotericin B on Leishmania sp

The mode of action of the polyene antibiotic amphotericin B (AmB), the drug of choice for the treatment of systemic fungal infections and visceral leishmaniasis, is still unclear. An increase in intracellular Ca2+ concentration ( Ca2+i), toxic in many cases, has been postulated as a possible lethal mechanism for AmB. Cell permeabilization to ethidium bromide (EB) was used as a criterion of viability. Kinetics of the DNA-EB fluorescent complex formation was studied in ergosterol-containing Leishmania promastigotes. Intracellular Ca2+ concentration was measured using quin-2 fluorescence in parallel aliquots. It is shown in this work that AmB can act as an efficient Ca2+ ionophore. However, the rapid permeabilization effect induced by AmB on these cells was not dependent on an increase in Ca2+i. On the contrary, it was found that leishmanicidal effect of AmB was enhanced in the absence of external calcium. Furthermore, A23187 a Ca2+ ionophore did not provoke cell permeabilization to EB.