K. Kirk et al., GLUCOSE-UPTAKE IN PLASMODIUM-FALCIPARUM-INFECTED ERYTHROCYTES IS AN EQUILIBRATIVE NOT AN ACTIVE PROCESS, Molecular and biochemical parasitology, 82(2), 1996, pp. 195-205
The uptake of glucose into human erythrocytes infected with Plasmodium
falciparum was investigated using a number of different glucose analo
gues. In short time-courses with cells suspended in media containing 5
mM glucose, 2-deoxy-D-glucose equilibrated rapidly between the intrac
ellular and extracellular compartments. Its transport into the infecte
d cell was primarily via the host cell (cytochalasin B-sensitive) tran
sporter. 2-Deoxy-D-glucose did permeate the broad-specificity pathway
that is induced in infected cells by the intracellular parasite. Howev
er, this pathway made little contribution to the total uptake of 2-deo
xy-D-glucose under physiological conditions. In parasitised cells incu
bated with [C-14]2-deoxy-D-glucose for prolonged periods the intracell
ular 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 c
oncentration similar to that outside the cells. This transient intrace
llular accumulation of radiolabel was due entirely to the phosphorylat
ion of the [C-14]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 b
y 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 no
n-phosphorylated compounds 3-O-methyl-D-glucose and L-glucose) enter t
he intracellular parasite via a passive (i.e. equilibrative) rather th
an an active (i.e. concentrative) transport process.