FIG. 3.

Effect of l-proline on ATP production and infectivity of starved T. cruzi metacyclic forms (CL strain). (A) Parasites previously maintained in PBS for 36 h were incubated for 1 h with glucose (1 mM), l-proline (0.75 mM or 3.0 mM), or l-glutamic acid (1 mM). Afterward, the parasite ATP content and the ability to enter HeLa cells were examined. The numbers of intracellular parasites in 250 Giemsa-stained cells were counted. A reference value of 100% was assigned to the controls. Values represent the means ± standard deviations of the results of three independent experiments performed in duplicate. The differences between the results for the 36-h-starved and the l-proline-supplemented parasites were significant (P < 0.005). (B) Transport of glucose, l-proline, or glutamate was assayed by using radioactive compounds as described in Materials and Methods. At different time points after the addition of the radioactive reagent, the uptake was stopped by adding cold glucose, l-proline, or l-glutamic acid in PBS. Values represent the means ± standard deviations of the results of triplicate experiments. (C) Parasites were treated with inhibitors of energy production (rotenone [200 μM] and antimycin A [0.5 μM]) for 30 min, washed in PBS, and then used for cell invasion assays in the absence or presence of 1 mM glucose, 0.75 mM l-proline, or 1 mM l-glutamate. Intracellular parasites were counted in 250 Giemsa-stained cells. Values represent the means ± standard deviations of the results of three independent experiments performed in duplicate.