Characterization of the myoâinositol transport system in Trypanosomaâcruzi
2000; Wiley; Linguagem: Inglês
ISSN
1742-4658
AutoresMarcelo EinickerâLamas, Alessandra C. Almeida, Alex G. Todorov, Solange L. de Castro, Celso CarusoâNeves, Mécia M. Oliveira,
Tópico(s)Lysosomal Storage Disorders Research
ResumomyoâInositol is a growth factor for mammalian cells as well as for the pathogenic protozoa Trypanosomaâcruzi. Most of the cell surface molecules in this organism rely on myoâinositol as the biosynthetic precursor for phosphoinositides and glycosylated phosphatidylinositols. The aim of this work was to investigate the process of myoâinositol translocation across the parasite cell membrane. myoâInositol uptake was concentrationâdependent in the concentration range 0.1â10âµm with maximal transport obtained at 8âµm. Using sodiumâfree buffers, where Na+ was replaced by choline or K+, myoâinositol uptake was inhibited by 50%. Furosemide, an inhibitor of the ouabainâinsensitive Na+âATPase, inhibited the Na+âdependent and Na+âindependent myoâinositol uptake by 68 and 33%, respectively. In contrast, ouabain, an (Na++/K+) ATPase inhibitor, did not affect transport. Part of the myoâinositol uptake is mediated by active transport as it was inhibited when energy metabolism inhibitors such as carbonyl cyanide pâ(trifluoromethoxy)âphenylhydrazone (34%), 2,4âdinitrophenol (50%), KCN (71%) and NaN3 (69%) were added to the medium, or the temperature of the medium was lowered to 4â°C. The addition of glucose (5â50âmm) or mannose (10âmm) did not change the myoâinositol uptake, whereas the addition of 10âmm nonlabeled myoâinositol totally inhibited this transport, indicating that the transporter is specific for myoâinositol. Phloretin (0.3âmm) and phoridzin (5âmm), but not cytochalasinâB, were efficient inhibitors of myoâinositol uptake. A portion of the accumulated myoâinositol is converted to inositol phosphates and phosphoinositides. These data show that myoâinositol transport in T.âcruzi epimastigotes is mediated by at least two specific transportersâââone Na+âdependent and the other Na+âindependent.
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