A Mg-dependent ecto-ATPase is increased in the infective stages of Trypanosoma cruzi

In this work, we describe the ability of living epimastigotes of Trypanosoma cruzi to hydrolyze extracellular ATP. In these intact parasites, there was a low level of ATP hydrolysis in the absence of any divalent metal (2.42±0.31 nmol Pi/h×10⁸ cells). ATP hydrolysis was stimulated by MgCl₂, and the Mg-dependent ecto-ATPase activity was 27.15±2.91 nmol Pi/h×10⁸ cells. The addition of MgCl₂ to the extracellular medium increased the ecto-ATPase activity in a dose-dependent manner. This stimulatory activity was also observed when MgCl₂ was replaced by MnCl₂, but not by CaCl₂ or SrCl₂. The apparent K_m for Mg-ATP^2– was 0.61 mM, and free Mg²⁺ did not increase the ecto-ATPase activity. This ecto-ATPase activity was insensitive to the inhibitors of other ATPase and phosphatase activities. To confirm that this Mg-dependent ATPase was an ecto-ATPase, we used an impermeant inhibitor, DIDS (4, 4.diisothiocyanostylbene 2-2-disulfonic acid) as well as suramin, an antagonist of P₂ purinoreceptors and inhibitor of some ecto-ATPases. These two reagents inhibited the Mg²⁺-dependent ATPase activity in a dose-dependent manner. A comparison among the Mg²⁺-ecto-ATPase activities of the three forms of T. cruzi showed that the noninfective epimastigotes were less efficient at hydrolyzing ATP than the infective trypomastigote and amastigote stages.