Glucose transporters insulin affecting

Figure 6.15 Regulation of the number of glucose transporters in the plasma membrane. The transporter affected is GLUT-4. It is unclear which translocation process is affected by insulin, physical activity or a change in the ATP/ADP concentration ratio. Effects on the translocation from within the cell to the membrane or vice versa are indicated here.

FIGURE 15-36 Control of glycogen synthesis from blood glucose in myocytes. Insulin affects three of the five steps in this pathway, but it is the effects on transport and hexokinase activity, not the change in glycogen synthase activity, that increase the flux toward glycogen. 

Sweeney, G., Keen, J., Somwar, R., Konrad, D., Garg, R., and Klip, A. 2001. High leptin levels acutely inhibit insulin-stimulated glucose uptake without affecting glucose transporter 4 translocation in 16 rat skeletal muscle cells. Endocrinology 142 4806-4812. 

Biguanides do not affect glycaemia in normal individuals and do not increase insulin output. However, because the liver is the dominant site of action in a physiological in vivo situation, hepatic glucose transport is reduced leading to an increased hepatic insulin sensitivity. 

Insulin stimulates the transport of glucose into adipose and muscle cells by promoting the recruitment of glucose transporters to the cell membrane (see Fig. 31.15C). Other tissues, such as the liver, brain, and red blood cells, have a different type of glucose transporter that is not as significantly affected by insulin. 

Disuccinimidyl suberate, a cross-linking agent, has been synthesized and used to probe the insulin-responsive D-glucose transport of the rat adipocyte. Incubation of cells with the reagent blocked methyl-a-D-glucopyranoside transport without affecting either basal hexose transport or simple diffusion as indicated by uptake in the presence of cytochalasin B. 

Although insulin probably affects glucose transport in muscle (see below), in liver a primary effect of insulin on hexokinase could not be excluded. Studies performed on dogs with complete end-to-side portocaval shunt, on dog liver perfused in situ, and on liver slices suggested that insulin had no effect on glucose uptake in liver. 

The modern view proposes that insulin binds to specific receptors in all tissues where it exerts an effect. When it affects glucose transport, the formation of an insulin-receptor complex stimulates a carrier protein. When it stimulates macromolecular synthesis, in-... 

Cao, H., Polansky, M.M., and Anderson, R.A. 2007. Cinnamon extract and polyphenols affect the expression of tristetraprolin, insulin receptor, and glucose transporter 4 in mouse 3T3-L1 adipocytes. Archives of Biochemistry and Biophysics. 59 214-222. 

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