Glucose Carrier

Like the glucose carrier, the carriers for large neutral amino acids, the so-called L-system - now designated LAT - are present at both sides of the endothelial cell membranes and transport at least 10 essential amino acids. The L-transporter at the BBB has a much higher transport capacity than those in other tissues. Its marked preference for phenylalanine analogs explains why the anticancer drugs melphalan and d,l-NAM-7 are transported by the L-system, as is the L-Dopa used to treat Parkinson s disease [42]. 

Wolffram, S., Block, M., and Ader, P., Quercetin-3-glucoside is transported by the glucose carrier SGLTl across the brush border membrane of rat small intestine, J. Nutr., 132, 630, 2002. 

The Na+-myoinositol cotransporter is 46% identical with the glucose carrier (Kwon et al., 1992). The Na+-proline (Nakao et al., 1987) and Na+-pantothenate (Jackowski and Alix, 1990) carriers from E. coli show 28% and 25% identity, respectively (Pajor et al., 1992), to the Na+ glucose transporter from rabbit intestine. 

Fig. 2. Internalization of insulin receptors and the recruitment of glucose carriers and IGF-II receptors. Occupied insulin receptors are constantly being recycled to and from the plasma membrane with a halftime of 20 min. Presumably, a very slow basal rate also occurs. Receptors can be down-regulated by degradation and up-regulated by increased synthesis. Internalization of the insulin receptor triggers glucose transporters and IGF-II receptors to be recruited to the plasma membrane in adipocytes. Whether these two proteins are in the same or different vesicles remains to be seen.

Gins may. also contribute to the mechanism whereby insulin activates glucose transport in adipocytes and heart. This has been suggested to be a two-step process where the first step involves the recruitment of inactive glucose carriers from an internal vesicle pool to the plasma membrane and the second step involves the activation of the newly inserted carriers in the plasma membrane (vide supra). It is possible that this second step may be controlled by Gins. The reasons for thinking that this may be so are related to observations that, under certain conditions, glucagon... 

Baly, D. L., and Horuk, R. (1987). Dissociation of insulin-stimulated glucose transport from the translocation of glucose carriers in rat adipose cells. /. 8iof. Chem. 26Z, 21-24. 

Autoradiographic Tracers for Neuronal Activation Studies Ex vivo autoradiography is also commonly used with the glucose analog [ C] 2-dcoxyglucose (2-DG) to provide maps of the metabolic demands of neurons (Sokoloff et al. 1977). [ C]2-DG is a substrate for facilitated glucose carriers in the blood-brain barrier... 

Other effects of iodide include the inhibition of glucose transport, presumably by reduction of the number of available glucose carriers in pig cells (Filetti et al, 1986), and the inhibition of amino acid and uridine uptake Kleiman de Pisarev et al., 1978 Pisarev and Itoiz, 1972). The relationship of these effects to the previously described effects is not known. 

The significance of these findings will become clearer when we discuss models for sugar transport in another chapter. Suffice it to point out now that such observations were at the origin of the theory of the sodium-glucose carrier complex. 

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