Characterization of glycerol uptake in bloodstream and procyclic forms of Trypanosoma brucei.
Uptake of glycerol was studied in bloodstream and insect forms of the African parasite Trypanosoma brucei using [14C]glycerol in combination with the oil centrifugation technique. Our kinetic measurements revealed that in bloodstream forms glycerol appeared to be transported by two different mechanisms: firstly by a facilitated-diffusion carrier showing a Km of 0.17 mM and a Vmax of 44 nmol 10(-8) cells min(-1) that predominates at low glycerol concentrations, and secondly by simple diffusion. The effects induced by various inhibitors suggest that uptake is neither sodium dependent nor proton-motive-force driven. The saturable component of transport was phloretin and cytochalasin B sensitive and could also be inhibited by the substrate analogue glyceraldehyde, which led to a 74% decrease in glycerol uptake. In insect forms, however, glycerol is taken up by simple diffusion only. Uptake was insensitive to mercury ions and was not influenced by a variety of different channel inhibitors. Our data show that in T brucei glycerol transport across the plasma membrane occurs by simple diffusion. In addition, bloodstream forms express a carrier protein which promotes a rapid transport at low glycerol concentrations. Expression of this transport protein may account for a selective secretion of intracellular glycerol which otherwise could become toxic for the parasite due to its specific compartmentation of glycolysis.
Wille
U
U
Physiologisch-chemisches Institut, Universität Tübingen, Germany.
Schade
B
B
Duszenko
M
M
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D001769:Blood / Q000469:parasitology*; D002454:Cell Differentiation; D003571:Cytochalasin B / Q000494:pharmacology; D004058:Diffusion; D005990:Glycerol / Q000031:analogs & derivatives / Q000378:metabolism*; D007700:Kinetics; D010693:Phloretin / Q000494:pharmacology; D014346:Trypanosoma brucei brucei / Q000166:cytology / Q000378:metabolism*
D003571:Cytochalasin B; D005990:Glycerol; D010693:Phloretin