Characterization of the myo-inositol transport system in Trypanosoma cruzi.
myo-inositol is a growth factor for mammalian cells as well as for the pathogenic protozoa Trypanosoma cruzi. Most of the cell surface molecules in this organism rely on myo-inositol as the biosynthetic precursor for phosphoinositides and glycosylated phosphatidylinositols. The aim of this work was to investigate the process of myo-inositol translocation across the parasite cell membrane. myo-Inositol uptake was concentration-dependent in the concentration range 0.1-10 microM with maximal transport obtained at 8 microM. Using sodium-free buffers, where Na+ was replaced by choline or K+, myo-inositol uptake was inhibited by 50%. Furosemide, an inhibitor of the ouabain-insensitive Na+-ATPase, inhibited the Na+-dependent and Na+-independent myo-inositol uptake by 68 and 33%, respectively. In contrast, ouabain, an (Na++/K+) ATPase inhibitor, did not affect transport. Part of the myo-inositol uptake is mediated by active transport as it was inhibited when energy metabolism inhibitors such as carbonyl cyanide p-(trifluoromethoxy)-phenylhydrazone (34%), 2,4-dinitrophenol (50%), KCN (71%) and NaN3 (69%) were added to the medium, or the temperature of the medium was lowered to 4 degrees C. The addition of glucose (5-50 mM) or mannose (10 mM) did not change the myo-inositol uptake, whereas the addition of 10 mM nonlabeled myo-inositol totally inhibited this transport, indicating that the transporter is specific for myo-inositol. Phloretin (0.3 mM) and phoridzin (5 mM), but not cytochalasin B, were efficient inhibitors of myo-inositol uptake. A portion of the accumulated myo-inositol is converted to inositol phosphates and phosphoinositides. These data show that myo-inositol transport in T. cruzi epimastigotes is mediated by at least two specific transporters - one Na+-dependent and the other Na+-independent.
Einicker-Lamas
M
M
Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Brasil. einicker@biof.ufrj.br
Almeida
A C
AC
Todorov
A G
AG
de Castro
S L
SL
Caruso-Neves
C
C
Oliveira
M M
MM
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D027682:Cation Transport Proteins; D002851:Chromatography, High Pressure Liquid; D007294:Inositol / Q000378:metabolism*; D007295:Inositol Phosphates / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D014349:Trypanosoma cruzi / Q000201:enzymology / Q000378:metabolism*
D027682:Cation Transport Proteins; D007295:Inositol Phosphates; D007294:Inositol; D000255:Adenosine Triphosphate; D012964:Sodium; D000251:Adenosine Triphosphatases; C021838:sodium-translocating ATPase