AJP - Regulatory, Integrative and Comparative Physiology, Vol 249, Issue 1 139-R144, Copyright © 1985 by American Physiological Society
Monosaccharide transport into hemocytes of a sipunculan worm Themiste dyscrita
R. L. Ingermann, R. E. Hall, J. M. Bissonnette and R. C. Terwilliger
The hemerythrin-containing blood cells, or hemocytes, of the sipunculan
worm Themiste dyscrita were found to have a stereospecific and
nonconcentrative monosaccharide transport system. The transport system
transferred both D-glucose and 3-O-methyl-D-glucose (3-OMG), and transport
into cells by this system was rapid, reaching 50% equilibrium in
approximately 20 s at 10 degrees C with an initial concentration gradient
of 0.1 mM; the contribution to total uptake by simple diffusion was very
small. 3-OMG uptake showed saturation kinetics with a low half-saturation
constant (Km less than or equal to 0.1 mM). The uptake of labeled 3-OMG by
the hemocytes was strongly inhibited by unlabeled 3-OMG, 2-deoxy-D-glucose,
alpha- and beta-D-glucose, D-galactose, and D-mannose. It was moderately
inhibited by D-xylose, only slightly by alpha-methyl-D-glucoside and
D-fructose, and uninhibited by sucrose, L-glucose, or D-sorbitol. Phloretin
was more potent than phloridzin in blocking entry of 3-OMG. Cytochalasin B
did not bind tightly to the T. dyscrita transporter and was not a potent
inhibitor of transport; it half-maximally inhibited 3-OMG transport at 0.1
mM. Therefore, despite some differences the data suggest functional
similarities in the mechanism of monosaccharide transport into blood cells
of mammals and this invertebrate.
