Reassessment of insulin effects on the Vmax and Km values of hexose transport in isolated rat epididymal adipocytes.

Toyoda, Nagayasu; Flanagan, J E; Kôno, Tetsuro

doi:10.1016/s0021-9258(18)61568-6

Cited by 56 publications

(3 citation statements)

References 25 publications

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“…the prescribed conditions, we did not witness a significant "slow phase" of methylglucose equilibration in stimulated cells after 20 s as commented on by Toyoda et al (1987), and illustrated by Okuno and Gliemann (1987). By use of the equilibrium space from the methylglucose uptake time course fitting, the glucose data were fit to the model with = 0.039 s'1, k = 96 yuL/(s-mL), and wX + k = 134 ± 13 qL/fs-mL), and clearance was virtually linear for several seconds.…”

Section: Resultssupporting

confidence: 62%

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Evidence for functionally distinct glucose transporters in basal and insulin-stimulated adipocytes

Whitesell¹,

Regen²,

Abumrad³

1989

Biochemistry

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The activity and Km of glucose transport of rat adipocytes are quite variable in the basal state. This could be due to differing levels of highly saturable transport against a background of less saturable transport. Such heterogeneity could lead to differing conclusions as to the Km of basal cells compared to insulin-stimulated cells depending on the choice of substrate, the range of concentrations tested, and the rigor of data analysis. In the present work, we used a cell preparation which was stable and partially activated by constant agitation. We used a two-component model to fit the concentration dependence of D-glucose uptake. We defined two parallel pathways of glucose entry, a high-affinity/low-capacity pathway and a low-affinity/high-capacity pathway. Both pathways were stereospecific and were inhibited by cytochalasin B. The low-affinity pathway in basal cells had 97% of the total capacity (Vmax) with a high Km (greater than 50 mM). A second pathway had a very low Km (less than 1 mM) and only 3% of the total capacity, but contributed to 30-60% of glucose uptake at 8 mM glucose. In insulin-stimulated cells, a pathway with a Km of 4-5 mM dominated and contributed 85% of glucose transport. The low-affinity but not the very high affinity pathway persisted in stimulated cells, but its contribution was only 10-15% of transport at 8 mM glucose. These results suggest the presence of at least two functionally distinct transporters whose respective contributions can be characterized by nonlinear regression of data over a wide range of glucose concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

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Section: Resultssupporting

confidence: 62%

“…In the present work, we have examined the kinetics of stereospecific D-[14C]glucose transport (corrected for l-[3H]glucose uptake) in rat adipocytes prepared as described by Okuno and Gliemann (1987) and stirred continuously as described by Toyoda et al (1987). This resulted in a relatively stable but partially activated preparation.…”

mentioning

confidence: 99%

Evidence for functionally distinct glucose transporters in basal and insulin-stimulated adipocytes

Whitesell¹,

Regen²,

Abumrad³

1989

Biochemistry

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“…-INSULIN STIM. An effect of this magnitude (>.~40-fold higher than basal) accounts entirely for the 15-30 fold increases in glucose transport that are typically observed in brown and white adipocytes following insulin stimulation (James et al, 1986a,b;Toyoda et al, 1987). This finding is of importance because it has been suggested that insulin may also stimulate glucose transport via a mechanism other than translocation.…”

mentioning

confidence: 86%

Immuno-localization of the insulin regulatable glucose transporter in brown adipose tissue of the rat.

Slot

Geuze

Gigengack

et al. 1991

The Journal of Cell Biology

837

607

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Abstract. Antibodies specific for the insulin-regulatable glucose transporter (GLUT 4) were used to immunolocalize this protein in brown adipose tissue from basal-and insulin-treated rats. Cryosections of fixed tissue were incubated with antibodies, which were subsequently labeled with Protein A/gold and examined by EM. Antibodies against albumin and cathepsin D were also used with gold particles of different sizes to identify early and late endosomes, respectively. Under basal conditions 99 % of the GLUT 4 labeling was located within the cell. Labeling was predominantly in the trans-Golgi reticulum and tubulo-vesicular structures elsewhere in the cytoplasm. In insulin-stimulated cells ,040% of the GLUT 4 labeling was at the cell surface, where it was randomly distributed, except for occasional clustering in coated pits. Moreover, after insulin treatment, GLUT 4 was also enriched in early endosomes. We conclude that translocation of GLUT 4 to the cell surface is the major mechanism by which insulin increases glucose transport. In addition, these results suggest that in the presence of insulin GLUT 4 recycles from the cell surface, probably via the coated pit-endosome pathway that has been characterized for cell surface receptors, and also that insulin causes the redistribution of GLUT 4 by stimulating exocytosis from GLUT 4-containing tubulo-vesicular structures, rather than by slowing endocytosis of GLUT 4.

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Role of Monosaccharide Transport Proteins in Carbohydrate Assimilation, Distribution, Metabolism, and Homeostasis

Cura

Carruthers

2012

Comprehensive Physiology

140

117

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The facilitated diffusion of glucose, galactose, fructose, urate, myoinositol, and dehydroascorbic acid in mammals is catalyzed by a family of 14 monosaccharide transport proteins called GLUTs. These transporters may be divided into three classes according to sequence similarity and function/substrate specificity. GLUT1 appears to be highly expressed in glycolytically active cells and has been coopted in vitamin C auxotrophs to maintain the redox state of the blood through transport of dehydroascorbate. Several GLUTs are definitive glucose/galactose transporters, GLUT2 and GLUT5 are physiologically important fructose transporters, GLUT9 appears to be a urate transporter while GLUT13 is a proton/myoinositol cotransporter. The physiologic substrates of some GLUTs remain to be established. The GLUTs are expressed in a tissue specific manner where affinity, specificity, and capacity for substrate transport are paramount for tissue function. Although great strides have been made in characterizing GLUT‐catalyzed monosaccharide transport and mapping GLUT membrane topography and determinants of substrate specificity, a unifying model for GLUT structure and function remains elusive. The GLUTs play a major role in carbohydrate homeostasis and the redistribution of sugar‐derived carbons among the various organ systems. This is accomplished through a multiplicity of GLUT‐dependent glucose sensing and effector mechanisms that regulate monosaccharide ingestion, absorption, distribution, cellular transport and metabolism, and recovery/retention. Glucose transport and metabolism have coevolved in mammals to support cerebral glucose utilization. © 2012 American Physiological Society. Compr Physiol 2:863‐914, 2012.

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Reassessment of insulin effects on the Vmax and Km values of hexose transport in isolated rat epididymal adipocytes.

Cited by 56 publications

References 25 publications

Evidence for functionally distinct glucose transporters in basal and insulin-stimulated adipocytes

Evidence for functionally distinct glucose transporters in basal and insulin-stimulated adipocytes

Immuno-localization of the insulin regulatable glucose transporter in brown adipose tissue of the rat.

Role of Monosaccharide Transport Proteins in Carbohydrate Assimilation, Distribution, Metabolism, and Homeostasis

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