Modulation Of Glucose Transport Research Articles

Nitric oxide: a new player in the modulation of energy metabolism.

Nitric oxide (NO) is a key messenger molecule in several cell types. NO formation is catalyzed by a family of NO synthases (NOS) that use L-arginine as a substrate. Rat adipose tissue expresses the inducible, macrophage-type, nitric oxide (NO) synthase isoform (iNOS). Systemic administration of the bacterial endotoxin lipopolysaccharide (LPS) markedly increases the expression and activity of iNOS in both white and brown adipose tissues, as well as in skeletal muscle. iNOS induction can be reproduced in vitro by treatment of cultured white or brown adipocytes or L6 myocytes with LPS and inflammatory cytokines (TNFalpha, IFNgamma). The physiological role of NO in adipose tissues and skeletal muscle is still obscure. Recent evidence suggests that NO may be implicated in the regulation of energy metabolism. Using both pharmacological and genetic models of iNOS invalidation, we have recently begun to uncover a role for NO in the modulation of glucose transport and lipoprotein hydrolysis. These studies support the emerging concept that NO may fulfill the dual role of modulating energy metabolism in both physiological and pathological conditions as well as contributing to local immune defense during inflammatory processes.

Preconditioning Enhanced Glucose Uptake Is Mediated by p38 MAP Kinase Not by Phosphatidylinositol 3-Kinase

Ischemia is reported to stimulate glucose uptake, but the signaling pathways involved are poorly understood. Modulation of glucose transport could be important for the cardioprotective effects of brief intermittent periods of ischemia and reperfusion, termed ischemic preconditioning. Previous work indicates that preconditioning reduces production of acid and lactate during subsequent sustained ischemia, consistent with decreased glucose utilization. However, there are also data that preconditioning enhances glucose uptake. The present study examines whether preconditioning alters glucose transport and whether this is mediated by either phosphatidylinositol 3-kinase (PI3K) or p38 MAP kinase. Langendorff-perfused rat hearts were preconditioned with 4 cycles of 5 min of ischemia and 5 min of reperfusion, with glucose as substrate. During the last reflow, glucose was replaced with 5 mM acetate and 5 mM 2-deoxyglucose (2DG), and hexose transport was measured from the rate of production of 2-deoxyglucose 6-phosphate (2DG6P), using (31)P nuclear magnetic resonance. Preconditioning stimulated 2DG uptake; after 15 min of perfusion with 2DG, 2DG6P levels were 165% of initial ATP in preconditioned hearts compared with 96% in control hearts (p < 0.05). Wortmannin, an inhibitor of PI3K, did not block the preconditioning induced stimulation of 2DG6P production, but perfusion with SB202190, an inhibitor of p38 MAP kinase, did attenuate 2DG6P accumulation (111% of initial ATP, p < 0. 05 compared with preconditioned hearts). SB202190 had no effect on 2DG6P accumulation in nonpreconditioned hearts. Preconditioning stimulation of translocation of GLUT4 to the plasma membrane was not inhibited by wortmannin. The data demonstrate that ischemic preconditioning increases hexose transport and that this is mediated by p38 MAP kinase and is PI3K-independent.

Biochemical and functional evidences for a GLUT-4 homologous protein in avian skeletal muscle.

The characteristics and modulation of glucose transport were investigated in skeletal muscles of 5-wk-old Muscovy ducklings (Cairina moschata). Glucose uptake by sarcolemmal vesicles isolated from gastrocnemius muscle followed typical Michaelis-Menten kinetics with a K(m) value (17 mM) similar to that described in equivalent mammalian preparations. Western blot analysis of duckling sarcolemma using antibodies directed against rat GLUT-4 transporter revealed an immunoreactive protein of similar molecular mass (45 kDa) to that present in rats. When ducklings were killed in the postabsorptive state, GLUT-4 homologous protein was located predominantly (80%) in intracellular membranes. Insulin stimulation of a perfused leg muscle preparation in vitro led to the translocation of GLUT-4 homologous proteins from intracellular pools to the sarcolemma, with a subsequent increase in glucose uptake by sarcolemmal vesicles and perfused muscles. Glucose transport was positively controlled by the metabolic needs of skeletal muscle as reflected by the increased glucose uptake of sarcolemmal vesicles isolated from cold-acclimated ducklings. Present results, therefore, demonstrate, for the first time in an avian species, the existence in skeletal muscle of a glucose transporter showing molecular and functional homologies with the mammalian GLUT-4 transporter.

O-192. Modulation of glucose transporter 4 in an in-vitro model of decidualized human endometrial cells

O-192. Modulation of glucose transporter 4 in an in-vitro model of decidualized human endometrial cells

Modulation of Glucose Transport in Fetal Rat Lung: A Sexual Dimorphism

Male fetuses exhibit delayed lung maturation and surfactant production in comparison with female fetuses. This delay may be related to sex hormone effects: estrogen enhances and androgens delay lung development. The uptake of glucose, an important precursor for surfactant synthesis, may be differently affected by estrogen and androgens. In these studies we determined the effects of these two hormones on glucose transport (glucose uptake, glucose transporter [Glut] 1 protein, and mRNA) and hexokinase activity in lung tissue of fetal rats. On Day 20 of gestation (term = 21.5 d) lung tissue was harvested from female and male fetal rats, minced into explants, and cultured for 24 h. Basal glucose uptake, measured in the absence of sex hormones, was 37% higher (P < 0.05) in female compared with male lungs. Explants were washed and cultured for an additional 3 h or 24 h in either estradiol or dihydrotestosterone (DHT) at 0, 1, 10, or 100 nM. Twenty-four-hour treatment with estradiol in both male and female explants increase 2-deoxyglucose uptake, Glut 1 protein, and mRNA levels (P < 0.05). However, explants from male fetuses were not as responsive to estradiol treatment as were those from females (P < 0.05). Treatment for 24 h with DHT decreased 2-deoxyglucose uptake, Glut 1 protein, and mRNA levels in females and males (P < 0.05). There was no difference in response between females and males. Short-term incubation (3 h) with sex hormones had no effect on glucose uptake. However, 3-h treatment with estradiol did increase Glut 1 mRNA levels (P < 0.05). Hexokinase activity was not affected by estradiol or DHT treatment. These findings indicate that estradiol and DHT differentially regulate glucose uptake in fetal rat lung tissue. This regulation of substrate supply (glucose) by estradiol and DHT may be another mechanism for the sexual dimorphism observed in lung development and surfactant synthesis.

17 beta-Estradiol modulation of glucose transporter 1 expression in blood-brain barrier.

The present study was designed to evaluate 17 beta-estradiol (E2) modulation of glucose transporter 1 (GLUT-1) protein and mRNA expression in blood-brain barrier (BBB) endothelium. Female rats were ovariectomized (OVX) for 12-14 days, then E2 was injected at dosages of 1-100 micrograms/kg sc at 2-16 h before sampling. Glucose transport into BBB endothelial cells was assessed using 2-deoxy-[14C]glucose (2-[14C]DG) uptake. GLUT-1 protein and mRNA samples were analyzed by Western and Northern blotting, respectively. E2 treatment caused dose- and time-dependent increases in 2-[14C]DG uptake and GLUT-1 protein expression by microvessels. The peak responses were induced by 10 micrograms/kg E2 dose at the 4-h sampling time (36.0 and 31.3% increases, P < 0.05, respectively). GLUT-1 mRNA demonstrated a transient increase at 15 min (55%, P < 0.05), then decreased to basal level by 2 h. This study shows that in vivo treatment with E2 increases 2-[14C]DG uptake into the BBB endothelial cells and suggests this E2 effect is due to its modulation of GLUT-1 mRNA and protein.

Prostanoid modulation of glucose transport in isolated diabetic rat uterus

3- O- 14C-methyl- d-Glucose (3- O-MG) transport and 14C-saccharose incorporation were measured in isolated uterine strips from ovariectomized-estrogenized diabetic rats. Glucose transport was decreased in uterine strips from diabetic rats compared with control animals. PGE 1 and PGE 2 (10 −7 M) stimulated 3- O-MG transport, PGF 2α failed to modify this parameter at the same concentration, while insulin (0.5 U/ml) evoked an improvement 30% greater than PGs. In spite of the negative influence exerted by TXA 2 over glucose metabolism in the isolated rat uterus, U46619, 10 −5 M (a TXA 2 analogue), and OKY064, 10 −7 M (an inhibitor of TXA 2 synthesis), failed to modify basal or insulin-treated hexose transport. Neither additive or synergistic interactions between PGE 1 or PGE 2 (10 −7 M) and insulin at 0.5 U/ml and 0.25 U/ml were detected. We conclude that the stimulatory action of PGE 1 and PGE 2 on glucose metabolism that has been previously described by us, involves enhancement of glucose transport.

Modulation of glucose transport by parathyroid hormone and insulin in UMR 106–01, a clonal rat osteogenic sarcoma cell line

This study characterizes the actions of insulin and parathyroid hormone (PTH) on the glucose transport system in the rat osteogenic sarcoma cell line UMR 106-01, which expresses a number of features of the osteoblast phenotype. Using [1,2-3H]2-deoxyglucose (2-DOG) as a label, UMR 106-01 cells were shown to possess a glucose transport system which was enhanced by insulin. In contrast, PTH influenced glucose transport in a biphasic manner with a stimulatory effect at 1 h and a more potent inhibitory effect at 16 h on basal and insulin-stimulated 2-DOG transport. To explore the mechanism of PTH action, a direct agonist of cAMP-dependent protein kinase (PKA) was tested. 8-Bromo-cAMP had no acute stimulatory effect but inhibited basal and insulin-stimulated 2-DOG transport at 16 h. This result suggested that the prolonged, but not the acute, effect of PTH was mediated by the generation of cAMP. Further studies with the cell line UMR 4-7, a UMR 106-01 clone stably transfected with an inducible mutant inactive regulatory subunit of PKA, confirmed that the inhibitory but not the stimulatory effect of PTH was mediated by the PKA pathway. Northern blot data indicated that the prolonged inhibitory effects of PTH and 8-bromo-cAMP on glucose transport were likely to be mediated in part by reduction in the levels of GLUT1 (HepG2/brain glucose transporter) mRNA.

Molecular basis for Na+-dependent glucose transport modulation by membrane fluidity

Molecular basis for Na+-dependent glucose transport modulation by membrane fluidity

Insulin and Insulin-like Growth Factor-1 Modulation of Glucose Transport in Arterial Smooth Muscle Cells: Implication of GLUT-4 in the Vasculature

Insulin modulates many physiological processes in vascular smooth muscle cells (VSMC) such as contractility, proliferation, and ion homeostasis. However, hormonal modulation of glucose transport has not been explored in pure populations of these cells. This study demonstrates that insulin and insulin-like growth factor-1 (IGF-1) increase glucose transport in a7r5 clonal and freshly prepared Sprague-Dawley aortic (SDa) VSMC. In a7r5 cells, physiologic (10(-12) to 10(-9) mol/L) insulin concentrations increase transport by 8% to 15%, whereas supraphysiologic concentrations (10(-9) to 10(-6) mol/L) increase transport by up to 60% (P < .05 v no increase over all concentrations tested). In SDa cells, insulin was more potent, displaying maximum transport stimulation of 70% at 10(-8) mol/L (P < .05 v a7r5 cells). Insulin regulation of glucose transport occurs by a protein synthesis-independent pathway as 10 mumol/L cycloheximide was without effect. Insulin produces these effects within 20 min of treatment, and cytochalasin B (10 mumol/L) inhibits both basal and insulin-stimulated glucose transport by 93% and 96%, respectively. Stimulation of insulin receptors alone, with 2.5 pg/mL insulin receptor-specific antibody, stimulates glucose transport by 20%, suggesting transport can be stimulated by an IGF-1 receptor independent mechanism. However, IGF-1 is a more potent stimulator of transport in both cell lines studied, with maximal stimulation (10(-8) mol/L IGF-1) of 60% and 80% in a7r5 and SDa cells, respectively (P < .05 v 10(-8) mol/L insulin in both cell lines). Insulin stimulation of glucose transport is specific for [D+]-glucose; [L-]-glucose does not compete for transport.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of insulin and insulin-like growth factor-I on glucose transport in normal and small for gestational age fetal rats.

In a model of asymmetric small for gestational age (SGA) fetal growth retardation, we have previously found that glucose transport is decreased in lung (an organ whose growth is restricted) and unaffected in brain (growth is normal). The SGA model alters a number of physiological and metabolic factors that may decrease glucose transport, thereby causing growth retardation. Specifically, insulin and insulin-like growth factor-I (IGF-I) concentrations are diminished in SGA fetuses. We hypothesized that the specific modulation by these factors of gene expression of a glucose transporter, Glut-1, is impaired. We performed bilateral uterine arterial ligation in pregnant rats on day 19 of gestation (term = 21.5 days) and obtained fetal brain, lung, and skeletal muscle on day 20. Lung and muscle explants and monolayers of glial cells and type II pneumocytes were cultured in the presence or absence of insulin or IGF-I for 24 h. Glucose uptake and levels of Glut-1 protein and mRNA were similar in brains of SGA and control fetuses and were not affected by treatment with insulin or IGF-I. Treatment with insulin or IGF-I increased glucose uptake and levels of Glut-1 protein and mRNA in a dose-dependent manner in lung and muscle from control fetuses. However, the response in SGA lung was not as great as that in controls. SGA muscle demonstrated no significant response to either hormone. These findings suggest that changes in glucose transport modulation might contribute to the development of asymmetric growth retardation, and that maintenance of normal transporter function and expression in brain may play a role in sparing its growth.

The effect of insulin and insulin-like growth factor-I on glucose transport in normal and small for gestational age fetal rats

In a model of asymmetric small for gestational age (SGA) fetal growth retardation, we have previously found that glucose transport is decreased in lung (an organ whose growth is restricted) and unaffected in brain (growth is normal). The SGA model alters a number of physiological and metabolic factors that may decrease glucose transport, thereby causing growth retardation. Specifically, insulin and insulin-like growth factor-I (IGF-I) concentrations are diminished in SGA fetuses. We hypothesized that the specific modulation by these factors of gene expression of a glucose transporter, Glut-1, is impaired. We performed bilateral uterine arterial ligation in pregnant rats on day 19 of gestation (term = 21.5 days) and obtained fetal brain, lung, and skeletal muscle on day 20. Lung and muscle explants and monolayers of glial cells and type II pneumocytes were cultured in the presence or absence of insulin or IGF-I for 24 h. Glucose uptake and levels of Glut-1 protein and mRNA were similar in brains of SGA and control fetuses and were not affected by treatment with insulin or IGF-I. Treatment with insulin or IGF-I increased glucose uptake and levels of Glut-1 protein and mRNA in a dose-dependent manner in lung and muscle from control fetuses. However, the response in SGA lung was not as great as that in controls. SGA muscle demonstrated no significant response to either hormone. These findings suggest that changes in glucose transport modulation might contribute to the development of asymmetric growth retardation, and that maintenance of normal transporter function and expression in brain may play a role in sparing its growth.

Cyclic AMP acutely stimulates translocation of the major insulin-regulatable glucose transporter GLUT4.

Facilitated glucose transport across plasma membranes is mediated by a family of transporters (GLUT1-GLUT5) that have different tissue distributions and Km values for transport. It has been shown that insulin stimulates glucose transport in fat and muscle tissues by causing the redistribution of one of these proteins (GLUT4) from inside the cell to the plasma membrane. Previous studies have shown that agents that change cAMP levels are able to modulate glucose transport in fat cells. The aim of this study was to investigate the mechanisms responsible for modulation of glucose transport by cAMP. 2-Deoxyglucose transport and insulin-regulatable glucose transporter (GLUT4) immunoreactivity in plasma and low density microsomal membranes were measured in adipocytes incubated for 30 min with insulin or dibutyryl-cAMP (Bt2cAMP). Low concentrations of Bt2cAMP (10 microM) increased 2-deoxyglucose uptake by translocating GLUT4 from low density microsomal membranes to the plasma membranes. Bt2cAMP at 1000 microM inhibited glucose transport below basal but further increased translocation of GLUT4. The effect of Bt2cAMP on translocation was additive to that of 7 nM insulin. We conclude that in rat adipocytes, Bt2cAMP acutely translocates GLUT4 but inhibits its activity to transport glucose.

Modulation of glucose transport in hamster adipocytes by insulin and by?- and? 2-adrenoceptor agonists

Glucose transport in hamster adipocytes and its modulation by insulin and isoprenaline was characterized with the aid of the non-metabolizable hexose 3-0-methylglucose. Insulin stimulated the initial uptake rates by an increase in Vmax of the transport without any detectable change in Km. The hormone concentration producing half maximal stimulation was identical to that required in rat adipocytes. However, hamster adipocytes were much less responsive to insulin (3-fold stimulation as compared to a 12-fold stimulation in rat fat cells), and maximal transport rates were 10-fold lower than that observed in rat adipocytes. Accordingly, the number of glucose transporters, as assessed by glucose-inhibitable cytochalasin-B binding, was considerably lower in plasma membranes of hamster adipocytes. Moreover, no transporters were detected in the low-density microsomes which in insulin-sensitive cell types represent the intracellular pool of recruitable glucose transporters. The relative insulin resistance of the hamster fat cells may therefore be due to a depleted pool of intracellular glucose transporters. In the presence of adenosine, the beta-adrenoceptor agonist isoprenaline produced a moderate stimulation of the basal transport rate which was antagonized by the alpha 2-agonist clonidine. If adenosine deaminase was added in order to remove endogenous adenosine, isoprenaline inhibited the insulin-stimulated transport by 50%. In contrast to the stimulatory effects of insulin and isoproterenol, the inhibitory effect of the catecholamine was reversed by cooling the cells to 22 degrees. Glucagon produced a comparable inhibition, suggesting that the inhibitory effect was mediated by adenylate cyclase or its regulatory subunits.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of glucose transport in human red blood cells by ATP

Depletion of energy stores of human red cells decreases the maximum transport capacity, J m , for glucose transport to a value one-third or less of that found in red cells from freshly drawn blood. There is no change in K m . Hemolysis and resealing of red cells with ATP or ADP reverses the decrease in J m . The maximum effect occurs at concentrations of ATP in the normal range for red cells, however, there is little effect from ADP concentrations in its normal range in freshly drawn red cells. Hemolysis and resealing with ATP gives an increase in J m and an increase in differential labeling by photolytic labeling with tritiated cytochalasin B. Most of the activation is lost after a second hemolysis-reseal without ATP but about 25% of the activation remains.

Dynamic aspects of glucose transport modulation in thymocytes.

Dynamic aspects of glucose transport modulation in thymocytes.