Influence Glucose Transport Research Articles

Efficacy of pectins with different degrees of methyl-esterification and of blockiness in preventing gut epithelial cell barrier disruption and the impact on sodium-glucose co-transporter expression under low and high glucose conditions.

Pectins support intestinal barrier function and have anti-diabetic effects, and can differ in the degree of methyl-esterification (DM) and the distribution of non-esterified galacturonic acid residues (DB). The mechanisms and effects of pectin type at different glucose levels are unknown. Pectins with different DM/DB on T84 cells were tested in the presence and absence of the barrier disruptor A23187 at 5 mM and 20 mM glucose. DM19 and DM43 pectins with high DB do rescue the intestinal barrier from disruption. Their effects were as strong as those of the barrier-rescuing anti-diabetic drug metformin, but effects with metformin were restricted to high glucose levels while pectins had effects at both low and high glucose levels. At high glucose levels, DM43HB pectin, which enhanced trans-epithelial electrical resistance, also increased the expressions of claudin1, occludin, and ZO-1. Low and high DM pectins decrease the apical expression of the sodium-glucose co-transporter (SGLT-1) and thereby influence glucose transport, explaining the anti-diabetogenic effect of pectin. Higher DB pectins had the strongest effect. Their impact on SGLT-1 was stronger than that of metformin. Pectin's rescuing effect on barrier disruption and its impact on glucose transportation and anti-diabetogenic effects depend on both the DB and the DM of pectins.

Phloretin Improves Ultrafiltration and Reduces Glucose Absorption during Peritoneal Dialysis in Rats.

Harmful glucose exposure and absorption remain major limitations of peritoneal dialysis (PD). We previously showed that inhibition of sodium glucose cotransporter 2 did not affect glucose transport during PD in rats. However, more recently, we found that phlorizin, a dual blocker of sodium glucose cotransporters 1 and 2, reduces glucose diffusion in PD. Therefore, either inhibiting sodium glucose cotransporter 1 or blocking facilitative glucose channels by phlorizin metabolite phloretin would reduce glucose transport in PD. We tested a selective blocker of sodium glucose cotransporter 1, mizagliflozin, as well as phloretin, a nonselective blocker of facilitative glucose channels, in an anesthetized Sprague-Dawley rat model of PD. Intraperitoneal phloretin treatment reduced glucose absorption by >30% and resulted in a >50% higher ultrafiltration rate compared with control animals. Sodium removal and sodium clearances were similarly improved, whereas the amount of ultrafiltration per millimole of sodium removed did not differ. Mizagliflozin did not influence glucose transport or osmotic water transport. Taken together, our results and previous results indicate that blockers of facilitative glucose channels may be a promising target for reducing glucose absorption and improving ultrafiltration efficiency in PD.

Interactions of dietary carbohydrate and vitamin D3 on growth performance, insulin signaling pathway and glucose metabolism in juvenile abalone Haliotis discus hannai

A 115-day feeding trial was conducted to investigate the effect of dietary carbohydrate and vitamin D3 levels, and their interactions on growth performance, body composition, insulin signaling pathway and glucose metabolism in juvenile abalone Haliotis discus hannai (initial body weight: 2.06 ± 0.01 g). Nine experimental diets in a 3 × 3 two-factor design were formulated with different carbohydrate levels (27.5%, 32% and 36.5%) and vitamin D3 levels (0, 1000 IU/kg and 5000 IU/kg). Results showed that the highest specific growth rate (SGR) of abalone was observed in the treatment with 36.5% of dietary carbohydrate and 1000 IU/kg of vitamin D3. The serum glucose, body crude lipid and muscle glycogen contents of abalone significantly increased with increasing dietary carbohydrate levels (P < 0.05). Diet with 1000 IU/kg of vitamin D3 significantly reduced the serum glucose and body crude lipid content (P < 0.05). Significant interactions between dietary carbohydrate and vitamin D3 were observed in SGR and crude lipid content (P < 0.05). Diet with 36.5% carbohydrate up-regulated the expression of pyruvate kinase, glucose-6-phosphate dehydrogenase (G6PDH), insulin receptor (IR), insulin receptor substrate (IRS), protein kinase B (Akt), glycogen synthase and glycogen phosphorylase (PYG), whereas decreased the phosphoenolpyruvate carboxykinase (PEPCK), glucose-6-phosphatase (G6P) and glycogen synthesis kinase-3β. Diet with 1000 IU/kg of vitamin D3 significantly up-regulated the hexokinase, IR, IRS, Akt and glucose transporter 1 mRNA levels, whereas decreased the G6PDH (P < 0.05). The interaction between dietary carbohydrate and vitamin D3 were significant on PEPCK, G6P, G6PDH and PYG mRNA levels (P < 0.05). In conclusion, dietary carbohydrates and vitamin D3 could affect glucose metabolism by regulating glycolysis, gluconeogenesis and pentose phosphate pathway in abalone. Besides, they triggered the insulin signaling pathway, and further influence glucose transport and glycogen synthesis, which could promote the utilization of carbohydrate in abalone.

Adiponectin stimulates glucose uptake in mouse blastocysts and embryonic carcinoma cells

Preimplantation embryos are sensitive to maternal hormones affecting embryonic signal transduction and metabolic functions. We examined whether adiponectin, the most abundantly secreted adipokine, can influence glucose transport in mouse embryonic cells. In mouse blastocysts full-length adiponectin stimulated glucose uptake, while no effect of globular adiponectin was found. Full-length adiponectin stimulated translocation of GLUT8 glucose transporter to the cell membrane; we did not detect significant changes in the intracellular localization of GLUT4 glucose transporter in adiponectin-treated blastocysts. To study adiponectin signaling in detail, we used embryoid bodies formed from mouse embryonic carcinoma cell (ECC) line P19. We confirmed the expression of adiponectin receptors in these cells. Similar to mouse blastocysts, full-length adiponectin, but not globular adiponectin, stimulated glucose uptake in ECC P19 embryoid bodies. Moreover, full-length adiponectin stimulated AMPK and p38 MAPK phosphorylation. These results indicate that besides AMPK, p38 MAPK is a potential target of adiponectin in mouse embryonic cells. AMPK inhibitor did not influence the adiponectin-stimulated p38 MAPK phosphorylation, indicating independent action of these two signaling pathways. In mouse embryos adiponectin acts as a hormonal regulator of glucose uptake, which becomes especially important in phases with reduced levels of circulating insulin. Our results suggest that adiponectin maintains the glucose supply for early embryos under hypoinsulinaemic conditions, for example, in mothers suffering from type 1 diabetes mellitus.

Nexilin, a Cardiomyopathy-Associated F-Actin Binding Protein, Binds and Regulates IRS1 Signaling in Skeletal Muscle Cells

Insulin stimulates glucose uptake through a highly organized and complex process that involves movement of the glucose transporter 4 (GLUT4) from intracellular storage sites to the plasma membrane. Previous studies in L6 skeletal muscle cells have shown that insulin-induced activation and assembly of insulin receptor substrate 1 (IRS1) and p85α the regulatory subunit of the Type 1A phosphatidylinositol-3-kinase (PI3K), within remodeled actin-rich membrane structures is critical for downstream signalling mediating the translocation of GLUT4. The mechanism for localization within actin cytoskeletal scaffolds is not known, as direct interaction of IRS1 or p85α with F-actin has not been demonstrated. Here we show that nexilin, a F-actin binding protein implicated in the pathogenesis of familial dilated cardiomyopathies, preferentially binds to IRS1 over IRS2 to influence glucose transport in skeletal muscle cells. Nexilin stably associates with IRS1 under basal conditions in L6 myotubes and this complex is disassembled by insulin. Exposure of L6 myotubes to Latrunculin B disrupts the spatial patterning of nexilin and its transient association with IRS1. Functional silencing of nexilin has no effect on insulin-stimulated IRS1 tyrosine phosphorylation, however it enhances recruitment of p85α to IRS1 resulting in increased PI-3, 4, 5-P3 formation, coincident with enhanced AKT activation and glucose uptake. By contrast, overexpression of nexilin inhibits transmission of IRS1 signals to AKT. Based on these findings we propose that nexilin may tether IRS1 to actin-rich structures under basal conditions, confining IRS1 signaling to specific subcellular locations in the cell. Insulin-elicited release of this constraint may enhance the efficiency of IRS1/PI3K interaction and PI-3, 4, 5-P3 production at localized sites. Moreover, the selective binding of nexilin to IRS1 and not IRS2 may contribute to the differential specificity of IRS isoforms in the modulation of GLUT4 trafficking in skeletal muscle cells.

Cloning and Functional Characterization of Related TC10 Isoforms, a Subfamily of Rho Proteins Involved in Insulin-stimulated Glucose Transport

Insulin stimulates glucose transport via phosphatidylinositol 3-kinase-dependent and -independent pathways. The phosphatidylinositol 3-kinase-independent pathway involves activation of the G protein TC10. A cDNA encoding the mouse homolog of TC10 was cloned, and its gene was mapped at the distal end of chromosome 17. Additionally, a second gene was discovered with approximately 70% sequence identity to TC10. We refer to this gene as TC10beta. Both isoforms of TC10 were activated by insulin upon transfection in 3T3L1 adipocytes. Cotransfection of cells with TC10alpha or beta plus a dominant negative form of the c-cbl-associated protein CAP prevented the activation by insulin, implicating the CAP/Cbl pathway. Interestingly, both forms of TC10 were also localized in lipid raft fractions in transfected adipocytes. However, although overexpression of TC10alpha completely blocked glucose transport, TC10beta only partially inhibited this process. Furthermore, TC10alpha overexpression disrupted adipocyte cortical actin, whereas TC10beta had little if any effect. Thus, there are two isoforms of this key signaling intermediate, both of which are activated by insulin, but they may play different roles in initiating downstream effectors that influence glucose transport.

Calphostin C is an inhibitor of contraction, but not insulin-stimulated glucose transport, in skeletal muscle.

Wortmannin selectively impairs insulin-stimulated glucose transport in skeletal muscle. To search for an inhibitor specific for contraction-stimulated glucose transport, we screened a number of calmodulin and PKC inhibitors for their ability to impair contraction- and insulin-stimulated 2-deoxyglucose uptake in incubated rat soleus muscles. In concentrations that did not reduce contraction-induced force output, among calmodulin inhibitors W-7 inhibited both contraction- and insulin-stimulated glucose transport by up to 50% (P < 0.05), while Calmidazolium impaired only insulin-stimulated glucose transport (P < 0.05), and Trifluoperazine and Phenoxybenzamine did not influence glucose transport. In concentrations that did not reduce force generation, among PKC inhibitors Calphostin C specifically inhibited contraction-stimulated glucose transport (P < 0.05), whereas insulin-stimulated transport was impaired by Rottlerin and Bisindolylmaleimide I (P < 0.05), and both contraction- and insulin-stimulated glucose transport were inhibited by RO-31-8220 (P < 0.05). Calphostin C did not reduce contraction-induced increase in AMP-activated protein kinase (AMPK) activity. In conclusion, we have identified specific inhibitors of both contraction- and insulin-stimulated glucose transport. Both calmodulin and different isoenzymes of the PKC family may be involved in contraction- and insulin-stimulated glucose transport. Calphostin C does not influence glucose transport during contractions via stimulation of AMPK. Calphostin C may be used to unravel signal transduction in contraction-stimulated glucose transport.

Effects of epinephrine on glucose metabolism in contracting rat skeletal muscles.

The effects of epinephrine on glucose metabolism during contractile activity and insulin stimulation were investigated in fast-twitch (epitrochlearis) and slow-twitch (soleus) muscles from Wistar rats. All muscles were mounted on contraction apparatuses, and some muscles were stimulated electrically for 30 min in vitro. Glucose uptake and glucose phosphorylation were measured with 2-[1, 2-3H(N)]deoxy-D-glucose and glucose transport with 3-O-[methyl-3H]methyl-D-glucose. D-[1-14C]mannitol was used to correct for extracellular space. In epitrochlearis, both contraction and insulin increased glucose transport by threefold, and combined they showed an additive effect. Epinephrine (10(-6) M) did not influence glucose transport across the membrane during contractile activity or insulin stimulation. In the absence of epinephrine, similar glucose phosphorylation was obtained during contraction and during insulin stimulation in epitrochlearis ( approximately 12 mmol . kg dry wt-1 . 30 min-1). In the presence of epinephrine, 9.5 +/- 0. 6 mmol . kg dry wt-1 . 30 min-1 glucose was phosphorylated during contraction, whereas only 2.0 +/- 0.3 mmol . kg dry wt-1 . 30 min-1 was phosphorylated during insulin stimulation (P < 0.01), despite a similar glucose 6-phosphate concentration. Comparable results were obtained in soleus. In conclusion, our data suggest that epinephrine inhibits glucose phosphorylation much less during contraction than during insulin stimulation.

Perfusion-Independent Effect of Bradykinin and Fosinoprilate on Glucose Transport in Langendorff Rat Hearts

Angiotensin-converting enzyme (ACE) inhibitor-stimulated glucose metabolism and perfusion in muscle tissue seem to be, at least in part, mediated by kinins. However, the relative contribution of direct metabolic or secondary hemodynamically induced effects is unclear. It was the aim of this study to characterize the effects of ACE inhibition and bradykinin on glucose transport while changes in cardiocoronary function that might influence glucose transport were minimized. Hearts from Wistar rats were perfused by a Langendorff preparation and a set of functional parameters were simultaneously measured. Bradykinin (10−11M) and fosinoprilate (10−7M) were administered at concentrations that did not affect coronary flow. Insulin was employed as reference at half-maximal concentration. The nonmetabolizable glucose analog 3-O-[14C]methyl-d-glucose and the nontransportable tracer l-[3H]glucose were coperfused for the calculation of glucose transport. Using a 2-compartment mathematical model we found that the glucose transport rate, which was doubled with insulin, was increased almost 3-fold by either bradykinin or fosinoprilate. In the presence of the B2 bradykinin receptor antagonist HOE 140 (d-Arg[Hyp3,Thi5,d-Tic7,Oic8]-bradykinin; icatibant), the effect of both agents was completely abolished. Both agents also induced minor changes in contractility/relaxation parameters that again were completely neutralized with icatibant. A perfusion-independent but B2-kinin receptor-dependent stimulating effect on glucose transport by either bradykinin or fosinoprilate is concluded. This effect could, in analogy to insulin be due to increased glucose transporter translocation, increased endothelium-derived nitric oxide formation, or—despite constant coronary flow conditions—secondary to altered cardiac function.

Action of metformin on glucose transport and glucose transporter GLUT1 and GLUT4 in heart muscle cells from healthy and diabetic rats.

The effects of the antidiabetic drug metformin on glucose transport were investigated in freshly isolated heart muscle cells from healthy and streptozotocin-diabetic rats. In vivo treatment of diabetic rats with metformin failed to affect the basal and insulin-stimulated rate of glucose transport measured in isolated cells. In vitro exposure to therapeutic concentrations (< or = 10(-4) M) of metformin did not influence glucose transport, even upon incubation times up to 5 h or in the presence of high glucose (20 nM). In contrast, higher metformin concentrations produced an 8- to 12-fold increase in glucose uptake (with a lag of 90 min, and a maximum at 180 min and approximately 5 mM). In the presence of submaximal insulin concentrations (< or = 3.10(-10) M), the effects of metformin (5 mM) and of insulin were more than additive, whereas, at saturating insulin concentrations (10(-8) M), partial additivity was observed. Like insulin, metformin caused an approximately 1.6-fold increase in the content of both glucose transporter isoforms GLUT1 and GLUT4 in the plasma membrane of cardiac myocytes, with a corresponding decrease in an intracellular membrane fraction. cAMP-elevating treatments depressed the metformin-, but not the insulin-dependent glucose uptake, by 20-30%. In myocytes from diabetic rats, the rate of metformin-activated glucose transport was similar to that of cells from control animals, whereas basal and insulin-stimulated transport were substantially diminished. Finally, metformin (5 mM) induced a slight depression of oxygen consumption and energy metabolism of myocytes (as determined by measuring their level of energy-rich phosphates) comparable to the effects of hypoxia in rat hearts. In conclusion, these data do not provide evidence in favor of the hypothesis that glucose uptake by muscle tissue represents the site of metformin's therapeutic action in vivo. On the other hand, the large, insulin-independent effect of metformin at high concentrations (approximately mM) in vitro may be related to the action of hypoxia and occurs through a redistribution of glucose carriers from an intracellular locus to the plasma membrane. The mechanism (or signal) involved in metformin's action is likely to differ from that triggered by insulin and is not impaired in the diabetic state.

Dietary Regulation of Glucose Transporter Gene Expression: Tissue Specific Effects in Adipose Cells and Muscle ,

The rapid stimulation of glucose transport into the classic insulin responsive tissues, muscle and adipose cells, is crucial for maintenance of glucose homeostasis in the fed state. Macronutrient content and composition of the diet strongly influence glucose transport into these tissues by altering both the expression of the glucose transporter genes (GLUT1 and GLUT4) and the functional activity of the gene products. Dietary regulation of GLUT1 and GLUT4 is tissue specific. With high fat feeding alterations in transporter expression is much greater in adipose cells than in skeletal muscle. In the unfed state there is a profound down regulation of glucose transporter gene expression in adipose cells while expression of the same transporter genes is increased in skeletal muscle. Thus, tissue specific regulation of glucose transporter expression and function appears to be part of the adaptive response to maintain adequate cellular nutrition in times of altered nutrient availability.

Forskolin inhibition of glucose transport in bone cell cultures through a cAMP-independent mechanism

Studies are presented demonstrating inhibition of glucose transport by forskolin in human MG-63 osteosarcoma cells as well as osteoblast-like cells derived from normal human trabecular bone and chick calvaria. The cAMP-stimulators parathyroid hormone, prostaglandin E 2, and isoproterenol did not influence glucose transport. Benzyl alcohol, a membrane lipid fluidity modulator, also provoked inhibition of the glucose uptake rate. Effects of forskolin and benzyl alcohol were not additive. It is suggested that cAMP is not a mediator of glucose transport in bone cells, and that forskolin inhibits glucose transport via a cAMP-independent mechanism.

Inhibition of Na +-stimulated glucose transport function and perturbation of intestinal microvillus membrane vesicles by ethanol and acetaldehyde

The effects of ethanol and acetaldehyde on rat intestinal microvillus membrane integrity and glucose transport function were examined in vitro with purified membrane vesicles. Ethanol could influence glucose transport function by alterations in the conformation of the carrier, the lipid environment surrounding the carrier, or in the transport driving force (Na + electrochemical gradient). Due to the rapid nature of glucose uptake, transport was assayed with the use of an apparatus that permitted uptake measurements as early as 1 s. Ethanol (340 m m) partially and acetaldehyde (44 m m) completely inhibited concentrative glucose uptake throughout the 1-min time course. Their inhibitory effects were reversible and irreversible, respectively. Kinetic measurements made during the initial rate of uptake (at 2 s) with various concentrations of glucose (0.05–8 m m) showed that ethanol and acetaldehyde both caused a decrease in V. Although ethanol did not substantially alter the transport K m , acetaldehyde increased the K m almost 50%. To determine whether ethanol or acetaldehyde directly interfered with glucose carrier function, uptake was measured in the presence of equilibrated Na +. Only acetaldehyde had a significant inhibitory effect under these conditions. Membrane permeability, as determined by efflux of preloaded 6-carboxyfluorescein dye, increased upon exposure of the vesicles to ethanol or acetaldehyde. Membrane fluidity measurements by fluorescence polarization showed that only acetaldehyde had a significant fluidizing effect. These results indicate that ethanol and acetaldehyde acted to perturb membrane integrity and inhibited glucose uptake indirectly by allowing the Na + gradient to dissipate. Acetaldehyde, which had a stronger inhibitory effect than ethanol, appeared also to directly inhibit carrier function.