in this work we describe the ability of living cells of Trypanosoma brucei brucei to hydrolyze extracellular ATP. In these intact parasites there was a low level of ATP hydrolysis in the absence of any divalent metal (4.72 +/- 0.51 nmol Pi x 10(-7) cells x h(-1)). The ATP hydrolysis was stimulated by MgCl2 and the Mg-dependent ecto-ATPase activity was 27.15 +/- 2.91 nmol Pi x 10(-7) cells x h(-1). This stimulatory activity was also observed when MgCl2 was replaced by MnCl2. CaCl2 and ZnCl2 were also able to stimulate the ATPase activity, although less than MgCl2. The apparent K-m for ATP was 0.61 mM. This ecto-ATPase activity was insensitive to inhibitors of other ATPase and phosphatase activities. To confirm that this Mg-dependent ATPase activity is an ecto-ATPase activity, we used an impermeable inhibitor, DIDS (4, 4'-diisothiocyanostylbene 2'-2'-disulfonic acid), as well as suramin, an antagonist of P-2 purinoreceptors and inhibitor of some ecto-ATPases. These two reagents inhibited the Mg2+-dependent ATPase activity in a dose-dependent manner. Living cells sequentially hydrolyzed the ATP molecule generating ADP, AMP and adenosine, and supplementation of the culture medium with ATP was able to sustain the proliferation of T brucei brucei as well as adenosine supplementation. Furthermore, the E-NTPDase activity of T brucei brucei is modulated by the availability of purines in the medium. These results indicate that this surface enzyme may play a role in the salvage of purines from the extracellular medium in T brucei brucei. (c) 2006 Elsevier Inc. All rights reserved.1154315323