Abstract
Macrophages play an important role against Trypanosoma cruzi infection, via superoxide, nitric oxide, and peroxynitrite production. Peroxynitrite has been shown to be highly cytotoxic against Trypanosoma cruzi epimastigotes. Calcium is involved in many vital functions of the parasites, being its intracellular concentration governed by several transport systems, involving mitochondrial and non-mitochondrial compartments. In this paper, we report the effect of peroxynitrite on the calcium uptake systems, as studied by digitonin-permeabilized trypanosomes in the presence of arsenazo III. Peroxynitrite, at biologically relevant concentrations produced within phagosomes (250–750 μM), inhibited calcium uptake in a dose-dependent manner. Peroxynitrite decreased the mitochondrial membrane potential obtained in the presence of tetramethyl- p-phenylenediamine (TMPD)/ascorbate. In addition, a decrease of the non-mitochondrial Ca 2+-uptake, concomitant with the inactivation of a Ca 2+-dependent ATPase activity, was observed. HPLC analyses of the cellular adenine nucleotide pool showed a time-dependent decrease of ATP content and energy charge of the parasite; however this drop in ATP levels was significantly delayed with respect to decrease of the ATP-dependent Ca 2+-transport. We conclude that the disruption of calcium homeostasis by peroxynitrite may contribute to the observed cytotoxic effects of macrophages against T. cruzi.
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