Glucose uptake in Plasmodium falciparum-infected erythrocytes is an equilibrative not an active process.
The uptake of glucose into human erythrocytes infected with Plasmodium falciparum was investigated using a number of different glucose analogues. In short time-courses with cells suspended in media containing 5 mM glucose, 2-deoxy-D-glucose equilibrated rapidly between the intracellular and extracellular compartments. Its transport into the infected cell was primarily via the host cell (cytochalasin B-sensitive) transporter. 2-Deoxy-D-glucose did permeate the broad-specificity pathway that is induced in infected cells by the intracellular parasite. However, this pathway made little contribution to the total uptake of 2-deoxy-D-glucose under physiological conditions. In parasitised cells incubated with [14C]2-deoxy-D-glucose for prolonged periods the intracellular concentration of radiolabel increased to values higher than that in the external medium; it reached a maximum value three to six times higher than the extracellular concentration before falling back to a concentration similar to that outside the cells. This transient intracellular accumulation of radiolabel was due entirely to the phosphorylation of the [14C]2-deoxy-D-glucose and its consequent trapping within the cell. The specific characteristics of the 2-deoxy-D-glucose uptake time courses measured under different conditions were accounted for by the kinetics of the phosphorylation process and the energy status of the cell. The data indicate that 2-deoxy-D-glucose (as well as the non-phosphorylated compounds 3-O-methyl-D-glucose and L-glucose) enter the intracellular parasite via a passive (i.e. equilibrative) rather than an active (i.e. concentrative) transport process.
Kirk
K
K
University Laboratory of Physiology, Oxford, UK. kiaran.kirk@anu.edu.au
Horner
H A
HA
Kirk
J
J
D019325:3-O-Methylglucose / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D002478:Cells, Cultured; D003847:Deoxyglucose / Q000378:metabolism; D004912:Erythrocytes / Q000378:metabolism* / Q000469:parasitology*; D005947:Glucose / Q000031:analogs & derivatives / Q000378:metabolism*; D006400:Hematocrit; D006801:Humans; D007700:Kinetics; D010766:Phosphorylation; D010963:Plasmodium falciparum / Q000378:metabolism*
D019325:3-O-Methylglucose; D000255:Adenosine Triphosphate; D003847:Deoxyglucose; D005947:Glucose