Ouabain-insensitive Na+-ATPase activity in Trypanosoma cruzi epimastigotes

in the present paper, the presence of a ouabain-insensitive Na+-stimulated, Mg2+-dependent ATPase activity in T. cruzi epimastigotes CL14 clone and Y strain was investigated. The increase in Na+ concentration (from 5 to 170 m M), in the presence of 2 mM ouabain, increases the ATPase activity in a sat urable manner along a rectangular hyperbola. The V-max was 18.0 +/- 1.0 and 21.1 +/- 1.1 moles Pi x mg(-1) x min(-1) and the half-activation value (K- 50) for Na+ was 34.3 +/- 5.8 mM and 37.7 +/- 5.3 in CL14 clone and in Y str ain, respectively. The Na+ stimulated ATPase activity was inhibited by 5-[a minosulfonyl]-3-chloro-2-[(2-furanylmethyl)-amino] benzoic acid (furosemide ) in a dose-dependent manner. The half-inhibition value (I-50) was 0.22 +/- 0.03 and 0.23 +/- 0.07 mM, and the Hill number (n) was 0.99 +/- 0.2 and 2. 16 +/- 0.29 for CL14 clone and Y strain, respectively. These data indicate that both cell types express the ouabain-insensitive Na+-ATPase activity, w hich might be considered the biochemical expression of the second Na+ pump.