RESUMO
In the small intestine transcellular and paracellular pathways are implicated in water-soluble nutrient absorption. In small birds the paracellular pathway is quantitatively important while transcellular pathway is much more important in terrestrial mammals. However, there is not a clear understanding of the mechanistic underpinnings of the differences among taxa. This study was aimed to test the hypothesis that paracellular permeability in perfused intestinal segments is higher in passerine birds than rodents. We performed in situ intestinal perfusions on individuals of three species of passerine birds (Passer domesticus, Taeniopygia guttata and Furnarius rufus) and two species of rodents (Mus musculus and Meriones ungiculatus). Using radio-labelled molecules, we measured the uptake of two nutrients absorbed by paracellular and transcellular pathways (L-proline and 3-O-methyl-D-glucose) and one carbohydrate that has no mediated transport (L-arabinose). Birds exhibited ~2 to ~3 times higher L-arabinose clearance per cm2 epithelium than rodents. Moreover, paracellular absorption accounted for proportionally more of 3-O-methyl-D-glucose and L-proline absorption in birds than in rodents. These differences could be explained by differences in intestinal permeability and not by other factors such as increased retention time or higher intestinal nominal surface area. Furthermore, analysis of our results and all other existing data on birds, bats and rodents shows that insectivorous species (one bird, two bats and a rodent) had only 30% of the clearance of L-arabinose of non-insectivorous species. This result may be explained by weaker natural selection for high paracellular permeability in animal- than in plant-consumers. Animal-consumers absorb less sugar and more amino acids, whose smaller molecular size allow them to traverse the paracellular pathway more extensively and faster than glucose.
Assuntos
3-O-Metilglucose/farmacocinética , Arabinose/farmacocinética , Gerbillinae/fisiologia , Mucosa Intestinal/fisiologia , Camundongos/fisiologia , Passeriformes/fisiologia , Prolina/farmacocinética , Animais , Transporte Biológico , Permeabilidade , Especificidade da EspécieRESUMO
The granulocyte-macrophage colony stimulating factor (GM-CSF) is a multifunctional cytokine implicated in proliferation, differentiation, and activation of several cell types including those involved in hematopoiesis and reproduction. In the present study, the expression of the α- and ß-subunit genes of GM-CSF receptor during follicular development in cattle was assessed. The spatial association of α- and ß-subunits of GM-CSF with follicle stimulating hormone receptor (FSHR) and 3ß-hydroxysteroid dehydrogenase (3ß-HSD), and the temporal associations with gene expression of hexose transporters (GLUTs) in granulosa cells of cattle were also evaluated. The effect of GM-CSF on the functionality of hexose transporters was also determined in an in vitro primary culture of granulosa cells. The spatial association of subunits of the GM-CSF receptor with 3ß-HSD and FSHR suggests a potential steroidogenic regulation of GM-CSF in granulosa cells. Immunodetection of GLUTs and uptake kinetic assays confirmed expression and functionality of these genes for hexose transporters in granulosa cells of cattle. Treatment of granulosa cells with GM-CSF, FSH or insulin- like growth factor-I (IGF-I) alone increased 2-deoxyglucose (DOG) or 3-0-methylglucose (OMG) uptake; however, when cells were treated with various combination of these factors there were no additive effect. Unexpectedly, the combination of GM-CSF and FSH decreased DOG uptake compared to FSH treatment alone. Thus, the expression pattern of GM-CSF receptor subunit genes during follicle development in cattle and promotion of DOG and OMG uptake in granulosa cells indicate a role for GM-CSF, FSH and/or IGF-I alone in regulating granulosa cell metabolic activity, specifically by promoting glucose uptake.
Assuntos
Bovinos/fisiologia , Glucose/metabolismo , Células da Granulosa/efeitos dos fármacos , Folículo Ovariano/metabolismo , Receptores de Fator Estimulador das Colônias de Granulócitos e Macrófagos/fisiologia , 3-Hidroxiesteroide Desidrogenases/genética , 3-Hidroxiesteroide Desidrogenases/metabolismo , 3-O-Metilglucose/metabolismo , Animais , Desoxiglucose/metabolismo , Feminino , Hormônio Foliculoestimulante/metabolismo , Regulação da Expressão Gênica/fisiologia , Fator Estimulador de Colônias de Granulócitos e Macrófagos/metabolismo , Fator de Crescimento Insulin-Like I/metabolismo , Proteínas de Transporte de Monossacarídeos/genética , Proteínas de Transporte de Monossacarídeos/metabolismo , Subunidades Proteicas , Traçadores Radioativos , Receptores do FSH/genética , Receptores do FSH/metabolismo , Fatores de TempoRESUMO
Dynamic positron emission tomography (PET) imaging was performed using sequential tracer injections ([(15)O]H2O, [(11)C]3-O-methylglucose [3-OMG], and [(18)F]fluorodeoxyglucose [FDG]) to quantify, respectively, skeletal muscle tissue perfusion (glucose delivery), kinetics of bidirectional glucose transport, and glucose phosphorylation to interrogate the individual contribution and interaction among these steps in muscle insulin resistance (IR) in type 2 diabetes (T2D). PET imaging was performed in normal weight nondiabetic subjects (NW) (n = 5), obese nondiabetic subjects (OB) (n = 6), and obese subjects with T2D (n = 7) during fasting conditions and separately during a 6-h euglycemic insulin infusion at 40 mU · m(-2) · min(-1). Tissue tracer activities were derived specifically within the soleus muscle with PET images and magnetic resonance imaging. During fasting, NW, OB, and T2D subjects had similar [(11)C]3-OMG and [(18)F]FDG uptake despite group differences for tissue perfusion. During insulin-stimulated conditions, IR was clearly evident in T2D (P < 0.01), and [(18)F]FDG uptake by muscle was inversely correlated with systemic IR (P < 0.001). The increase in insulin-stimulated glucose transport was less (P < 0.01) in T2D (twofold) than in NW (sevenfold) or OB (sixfold) subjects. The fractional phosphorylation of [(18)F]FDG during insulin infusion was also significantly lower in T2D (P < 0.01). Dynamic triple-tracer PET imaging indicates that skeletal muscle IR in T2D involves a severe impairment of glucose transport and additional impairment in the efficiency of glucose phosphorylation.
Assuntos
Diabetes Mellitus Tipo 2/metabolismo , Glucose/metabolismo , Resistência à Insulina , Músculo Esquelético/metabolismo , Obesidade/metabolismo , Tomografia por Emissão de Pósitrons/métodos , 3-O-Metilglucose/farmacocinética , Adulto , Transporte Biológico , Feminino , Fluordesoxiglucose F18/farmacocinética , Humanos , Masculino , Pessoa de Meia-Idade , FosforilaçãoRESUMO
Water-soluble nutrients are absorbed by the small intestine via transcellular and paracellular processes. The capacity for paracellular absorption seems lower in nonfliers than in fliers, although that conclusion rests largely on a comparison of relatively larger nonflying mammals (>155g) and relatively smaller flying birds (<155g). We report on paracellular absorption in laboratory mice, the smallest nonflying mammal species studied to date. Using a standard pharmacokinetic technique, we measured the extent of absorption (fractional absorption=f) of inert carbohydrate probes: L-arabinose (M(r)=150.13Da) and cellobiose (342.3) that are absorbed exclusively by the paracellular route, and 3-O-methyl D-glucose (3OMD-glucose) (M(r)=194) absorbed both paracellularly and transcellularly. f was measured accurately in urine collection trials of 5-10h duration. Absorption of 3OMD-glucose by mice was essentially complete (f=0.95±0.07) and much higher than that for L-arabinose (f=0.21±0.02), indicating that in mice, like other nonflying mammals, >80% of glucose is absorbed by mediated process(es) rather than the passive, paracellular route. As in all other vertebrates, absorption of cellobiose (f=0.13±0.02) was even lower than that for L-arabinose, suggesting an equivalent molecular size cut-off for flying and nonflying animals and thus a comparable effective TJ aperture. An important ecological implication is that smaller water-soluble plant secondary metabolites that have been shown to be absorbed by the paracellular path in cell culture, such as phenolics and alkaloids, might be absorbed in substantial amounts by bats and small birds relative to nonflying mammals such as mice.
Assuntos
3-O-Metilglucose/farmacocinética , Arabinose/farmacocinética , Celobiose/farmacocinética , Glucose/metabolismo , Absorção Intestinal , 3-O-Metilglucose/administração & dosagem , 3-O-Metilglucose/urina , Animais , Arabinose/administração & dosagem , Arabinose/urina , Transporte Biológico Ativo , Radioisótopos de Carbono/metabolismo , Celobiose/administração & dosagem , Celobiose/urina , Cromatografia Líquida de Alta Pressão , Enterócitos/metabolismo , Feminino , Masculino , Camundongos , Camundongos Endogâmicos ICR , Peso Molecular , Especificidade da Espécie , Fatores de TempoRESUMO
Sucrose synthase (SUS) is a key enzyme of carbon metabolism in heterotrophic tissues of plants. The Arabidopsis genome contains six SUS genes. Two members of this family, namely AtSUS2 (At5g49190) and AtSUS3 (At4g02280) are strongly and differentially expressed in Arabidopsis seed. Expression analysis was carried out using SUS:promoter-GUS fusion lines in a wild-type genetic background or in a mutant carrying a lesion in the transcription factor LEAFY COTYLEDON 2 (LEC2; At1g28300). The accumulation patterns of mRNA, protein, and SUS activity were altered in the lec2 mutant during seed development 9-18 days after flowering. This indicates that LEC2 acts epistatically on the expression of AtSUS2 and AtSUS3. It appears that LEC2 is required for cotyledon-specific expression of both SUS genes but it is not responsible for expression in the radicle tip during embryo development. The AtSUS2 promoter was induced in planta by feeding of glucose but less so by sucrose and trehalose. Non-phosphorylable glucose analogs such as 3-O-methyl-glucose and 2-deoxyglucose also caused an induction, suggesting that sugar signaling proceeds by a hexokinase-independent pathway, possibly involving hexose sensing. Analysis of transgenic lines carrying of truncated versions of the AtSUS2:promoter fused to Beta-glucuronidase activity revealed an internal 421 bp region that was responsible for expression in seeds. Bioinformatic sequence analysis revealed regulatory cis-elements putatively responsible for the spatio-temporal pattern of AtSUS2 expression such as the SEF3 (aaccca) and W-box (ttgact) motifs. These findings are discussed in relation to the roles played by AtSUS2, AtSUS3 and LEC2 in the biosynthesis of seed storage products in Arabidopsis.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/genética , Glucose/metabolismo , Sementes/crescimento & desenvolvimento , Fatores de Transcrição/metabolismo , 3-O-Metilglucose/farmacologia , Arabidopsis/efeitos dos fármacos , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Sítios de Ligação , Cotilédone/genética , Desoxiglucose/farmacologia , Flores , Regulação da Expressão Gênica de Plantas , Glucose/farmacologia , Glucosiltransferases/genética , Glucosiltransferases/metabolismo , Glucuronidase/genética , Glucuronidase/metabolismo , Família Multigênica , Mutação , Plantas Geneticamente Modificadas , Regiões Promotoras Genéticas , Sementes/genética , Sementes/metabolismo , Sacarose/metabolismo , Sacarose/farmacologia , Fatores de Transcrição/genética , Trealose/metabolismo , Trealose/farmacologiaRESUMO
Gossypol is a natural disesquiterpene that blocks the activity of the mammalian facilitative hexose transporter GLUT1. In human HL-60 cells, which express GLUT1, Chinese hamster ovary cells overexpressing GLUT1, and human erythrocytes, gossypol inhibited hexose transport in a concentration-dependent fashion, indicating that blocking of GLUT1 activity is independent of cellular context. With the exception of red blood cells, the inhibition of cellular transport was instantaneous. Gossypol effect was specific for the GLUT1 transporter since it did not alter the uptake of nicotinamide by human erythrocytes. Gossypol affects the glucose-displaceable binding of cytochalasin B to GLUT1 in human erythrocyte ghost in a mixed noncompetitive way, with a K(i) value of 20 microM. Likewise, GLUT1 fluorescence was quenched approximately 80% by gossypol, while Stern-Volmer plots for quenching by iodide displayed increased slopes by gossypol addition. These effects on protein fluorescence were saturable and unaffected by the presence of D-glucose. Gossypol did not alter the affinity of D-glucose for the external substrate site on GLUT1. Kinetic analysis of transport revealed that gossypol behaves as a noncompetitive inhibitor of zero-trans (substrate outside but not inside) transport, but it acts as a competitive inhibitor of equilibrium-exchange (substrate inside and outside) transport, which is consistent with interaction at the endofacial surface, but not at the exofacial surface of the transporter. Thus, gossypol behaves as a quasi-competitive inhibitor of GLUT1 transport activity by binding to a site accessible through the internal face of the transporter, but it does not, in fact, compete with cytochalasin B binding. Our observations suggest that some effects of gossypol on cellular physiology may be related to its ability to disrupt the normal hexose flux through GLUT1, a transporter expressed in almost every kind of mammalian cell and responsible for the basal uptake of glucose.
Assuntos
Eritrócitos/efeitos dos fármacos , Transportador de Glucose Tipo 1/antagonistas & inibidores , Glucose/metabolismo , Gossipol/farmacologia , 3-O-Metilglucose/metabolismo , Animais , Antígenos CD/genética , Antígenos CD/metabolismo , Sítios de Ligação , Ligação Competitiva , Células CHO , Cricetinae , Cricetulus , Citocalasina B/metabolismo , Desoxiglucose/metabolismo , Relação Dose-Resposta a Droga , Eritrócitos/metabolismo , Transportador de Glucose Tipo 1/genética , Transportador de Glucose Tipo 1/metabolismo , Gossipol/metabolismo , Células HL-60 , Humanos , Cinética , Modelos Biológicos , Niacinamida/metabolismo , Receptor de Insulina/genética , Receptor de Insulina/metabolismo , Espectrometria de Fluorescência , TransfecçãoRESUMO
Anecdotal evidence suggests that birds have smaller intestines than mammals. In the present analysis, we show that small birds and bats have significantly shorter small intestines and less small intestine nominal (smooth bore tube) surface area than similarly sized nonflying mammals. The corresponding >50% reduction in intestinal volume and hence mass of digesta carried is advantageous because the energetic costs of flight increase with load carried. But, a central dilemma is how birds and bats satisfy relatively high energy needs with less absorptive surface area. Here, we further show that an enhanced paracellular pathway for intestinal absorption of water-soluble nutrients such as glucose and amino acids may compensate for reduced small intestines in volant vertebrates. The evidence is that l-rhamnose and other similarly sized, metabolically inert, nonactively transported monosaccharides are absorbed significantly more in small birds and bats than in nonflying mammals. To broaden our comparison and test the veracity of our finding we surveyed the literature for other similar studies of paracellular absorption. The patterns found in our focal species held up when we included other species surveyed in our analysis. Significantly greater amplification of digestive surface area by villi in small birds, also uncovered by our analysis, may provide one mechanistic explanation for the observation of higher paracellular absorption relative to nonflying mammals. It appears that reduced intestinal size and relatively enhanced intestinal paracellular absorption can be added to the suite of adaptations that have evolved in actively flying vertebrates.
Assuntos
Adaptação Fisiológica , Quirópteros/fisiologia , Absorção Intestinal/fisiologia , Intestino Delgado/anatomia & histologia , Ramnose/farmacocinética , 3-O-Metilglucose/farmacocinética , Animais , Aves/anatomia & histologia , Aves/fisiologia , Peso Corporal , Quirópteros/anatomia & histologia , Metabolismo Energético , Voo Animal/fisiologia , Mamíferos/anatomia & histologia , Mamíferos/fisiologia , Camundongos , Tamanho do Órgão , Ratos , Especificidade da Espécie , Suporte de CargaRESUMO
Postmeiotic spermatogenic cells, but not meiotic spermatogenic cells respond differentially with glucose-induced changes in [Ca2+]i indicating a differential transport of glucose via facilitative hexose transporters (GLUTs) specifically distributed in the plasma membrane. Several studies have indicated that plasma membrane in mammalian cells is not homogeneously organized, but contains specific microdomains known as detergent-resistant membrane domains (DRMDs), lipid rafts or caveolae. The association of these domains and GLUTs isoforms has not been characterized in spermatogenic cells. We analyzed the expression and function of GLUT1 and GLUT3 in isolated spermatocytes and spermatids. The results showed that spermatogenic cells express both glucose transporters, with spermatids exhibiting a higher affinity glucose transport system. In addition, spermatogenic cells express caveolin-1, and glucose transporters colocalize with caveolin-1 in caveolin-enriched membrane fractions. Experiments in which the integrity of caveolae was disrupted by pretreatment with methyl-beta-cyclodextrin, indicated that the involvement of cholesterol-enriched plasma membrane microdomains were involved in the localization of GLUTs and uptake of 2-deoxyglucose. We also observed cofractionation of GLUT3 and caveolin-1 in low-buoyant density membranes together with their shift to higher densities after methyl-beta-cyclodextrin treatment. GLUT1 was found in all fractions isolated. Immunofluorescent studies indicated that caveolin-1, GLUT1, and hexokinase I colocalize in spermatocytes while caveolin-1, GLUT3, and hexokinase I colocalize in spermatids. These findings suggest the presence of hexose transporters in DRMDs, and further support a role for intact caveolae or cholesterol-enriched membrane microdomains in relation to glucose uptake and glucose phosphorylation. The results would also explain the different glucose-induced changes in [Ca2+]i in both cells.
Assuntos
Cavéolas/metabolismo , Transportador de Glucose Tipo 1/metabolismo , Transportador de Glucose Tipo 3/metabolismo , Hexoquinase/metabolismo , Espermátides/metabolismo , Espermatócitos/metabolismo , 3-O-Metilglucose/metabolismo , Animais , Transporte Biológico/efeitos dos fármacos , Cavéolas/química , Cavéolas/efeitos dos fármacos , Caveolina 1/análise , Caveolina 1/metabolismo , Membrana Celular/química , Membrana Celular/efeitos dos fármacos , Membrana Celular/metabolismo , Desoxiglucose/metabolismo , Transportador de Glucose Tipo 1/análise , Transportador de Glucose Tipo 3/análise , Hexoquinase/análise , Imuno-Histoquímica , Cinética , Masculino , Microscopia de Fluorescência , Ligação Proteica , Ratos , Ratos Sprague-Dawley , Espermátides/química , Espermátides/efeitos dos fármacos , Espermatócitos/química , Espermatócitos/efeitos dos fármacos , beta-Ciclodextrinas/farmacologiaRESUMO
The facilitative glucose transporter, GLUT4, mediates insulin-stimulated glucose uptake in adipocytes and muscles, and the participation of GLUT4 in the pathogenesis of various clinical conditions associated with obesity, visceral fat accumulation and insulin resistance has been proposed. Glucose uptake by some members of the GLUT family, mainly GLUT1, is inhibited by flavonoids, the natural polyphenols present in fruits, vegetables and wine. Therefore it is of interest to establish if these polyphenolic compounds present in the diet, known to be effective antioxidants but also endowed with several other biological activities such as protein-tyrosine kinase inhibition, interfere with GLUT4 function. In the present study, we show that three flavonoids, quercetin, myricetin and catechin-gallate, inhibit the uptake of methylglucose by adipocytes over the concentration range of 10-100 microM. These three flavonoids show a competitive pattern of inhibition, with K(i)=16, 33.5 and 90 microM respectively. In contrast, neither catechin nor gallic acid inhibit methylglucose uptake. To obtain a better understanding of the interaction among GLUT4 and flavonoids, we have derived a GLUT4 three-dimensional molecular comparative model, using structural co-ordinates from a GLUT3 comparative model and a mechanosensitive ion channel [PDB (Protein Data Bank) code 1MSL] solved by X-ray diffraction. On the whole, the experimental evidence and computer simulation data favour a transport inhibition mechanism in which flavonoids and GLUT4 interact directly, rather than by a mechanism related to protein-tyrosine kinase and insulin signalling inhibition. Furthermore, the results suggest that GLUT transporters are involved in flavonoid incorporation into cells.
Assuntos
Adipócitos/efeitos dos fármacos , Adipócitos/metabolismo , Catequina/análogos & derivados , Flavonoides/farmacologia , Glucose/metabolismo , Quercetina/farmacologia , 3-O-Metilglucose/metabolismo , Animais , Ligação Competitiva/efeitos dos fármacos , Transporte Biológico/efeitos dos fármacos , Catequina/química , Catequina/farmacologia , Simulação por Computador , Flavonoides/química , Flavonoides/metabolismo , Transportador de Glucose Tipo 4 , Cinética , Modelos Moleculares , Estrutura Molecular , Proteínas de Transporte de Monossacarídeos/química , Proteínas de Transporte de Monossacarídeos/metabolismo , Proteínas Musculares/química , Proteínas Musculares/metabolismo , Fosforilação/efeitos dos fármacos , Conformação Proteica , Quercetina/química , Quercetina/metabolismo , Ratos , Termodinâmica , Tirosina/metabolismoRESUMO
It has been proposed that GLUT1, a membrane protein that transports hexoses and the oxidized form of vitamin C, dehydroascorbic acid, is also a transporter of nicotinamide (Sofue, M., Yoshimura, Y., Nishida, M., and Kawada, J. (1992) Biochem. J. 288, 669-674). To ascertain this, we studied the transport of 2-deoxy-D-glucose, 3-O-methyl-D-glucose, and nicotinamide in human erythrocytes and right-side-out and inside-out erythrocyte membrane vesicles. The transport of nicotinamide was saturable, with a K(M) for influx and efflux of 6.1 and 6.2 mM, respectively. We found that transport of the hexoses was not competed by nicotinamide in both the erythrocytes and the erythrocyte vesicles. Likewise, the transport of nicotinamide was not affected by hexoses or by inhibitors of glucose transport such as cytochalasin B, genistein, and myricetin. On the other hand, nicotinamide blocked the binding of cytochalasin B to human erythrocyte membranes but did so in a noncompetitive manner. Using GLUT1-transfected CHO cells, we demonstrated that increased expression of GLUT1 was paralleled by a corresponding increase in hexose transport but that there were no changes in nicotinamide transport. Moreover, nicotinamide failed to affect the transport of hexoses in both control and GLUT1-transfected CHO cells. Therefore, our results indicates that GLUT1 does not transport nicotinamide, and we propose instead the existence of other systems for the translocation of nicotinamide across cell membranes.
Assuntos
Proteínas de Transporte de Monossacarídeos/metabolismo , Niacinamida/metabolismo , 3-O-Metilglucose/sangue , Animais , Células CHO/metabolismo , Cricetinae , Citocalasina B/antagonistas & inibidores , Citocalasina B/metabolismo , Citocalasina B/farmacologia , Desoxiglucose/sangue , Membrana Eritrocítica/metabolismo , Eritrócitos/efeitos dos fármacos , Eritrócitos/metabolismo , Flavonoides/farmacologia , Genisteína/farmacologia , Transportador de Glucose Tipo 1 , Humanos , Proteínas de Transporte de Monossacarídeos/antagonistas & inibidores , Proteínas de Transporte de Monossacarídeos/biossíntese , Proteínas de Transporte de Monossacarídeos/sangue , Niacinamida/sangue , Ligação Proteica/efeitos dos fármacos , Transfecção , Vesículas Transportadoras/metabolismoRESUMO
A fluorometric method that allows repeatable measurement of sugar transport rates and parameters in single living cells is presented. Intracellular sugar concentrations were estimated in real time from changes in cell volume that occur secondary to permeation of sugars across the plasma membrane. In turn, the cell volume changes were estimated from variations of intracellular calcein fluorescence measured by confocal microscopy. Using HeLa cells, the assay allowed reproducible measurement of the uptake and exit of D-galactose and 3-O-methyl-D-glucose. The rate of zero-trans uptake (i.e. at an intracellular concentration of zero) of galactose at an extracellular concentration of 200 mM was 0.34+/-0.05 mM/s (n=8). Apparent Vmax and Km for galactose exit were 0.32+/-0.05 mM/s (n=9) and 30+/-7.2 mM (n=9), respectively. The apparent affinity of infinite-trans (i.e. at a very high intracellular concentration) uptake of 3-O-methyl-D-glucose was 3.8+/-0.47 mM (n=8). Galactose uptake was 93+/-8% (n=8) inhibited in the presence of 50 microM phloretin, whereas galactose exit was 96+/-6% (n=5) trans-inhibited by 100 mM 4,6-ethylidine-D-glucose. This technique may help to characterize sugar transport in freshly isolated cells, co-cultures and heterogeneous cell explants. It may also allow available cell microinjection technology to be used to study the regulation of sugar transporters' intrinsic activity. In principle, similar approaches might also be applied in functional studies of other transporters for which non-metabolized substrates are available.
Assuntos
Metabolismo dos Carboidratos , Carboidratos/análise , 3-O-Metilglucose/metabolismo , Algoritmos , Transporte Biológico , Tamanho Celular , Fluoresceínas , Corantes Fluorescentes , Fluorometria , Galactose/metabolismo , Células HeLa , Humanos , Cinética , Microinjeções , Floretina/farmacologiaAssuntos
Células Epiteliais/metabolismo , Proteínas Quinases Ativadas por Mitógeno , Proteínas de Transporte de Monossacarídeos/metabolismo , 3-O-Metilglucose/metabolismo , Células 3T3 , Animais , Transporte Biológico/efeitos dos fármacos , Proteínas Quinases Dependentes de Cálcio-Calmodulina/metabolismo , Células Clonais , Desoxiglucose/metabolismo , Transportador de Glucose Tipo 1 , Camundongos , Concentração Osmolar , Ratos , Sorbitol/farmacologia , Estresse Fisiológico , Proteínas Quinases p38 Ativadas por MitógenoRESUMO
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. PGE1 and PGE2 (10(-7) M) stimulated 3-O-MG transport, PGF2 alpha 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 TXA2 over glucose metabolism in the isolated rat uterus, U46619, 10(-5) M (a TXA2 analogue), and OKY064, 10(-7) M (an inhibitor of TXA2 synthesis), failed to modify basal or insulin-treated hexose transport. Neither additive or synergistic interactions between PGE1 or PGE2 (10(-7) M) and insulin at 0.5 U/ml and 0.25 U/ml were detected. We conclude that the stimulatory action of PGE1 and PGE2 on glucose metabolism that has been previously described by us, involves enhancement of glucose transport.
Assuntos
3-O-Metilglucose/metabolismo , Alprostadil/farmacologia , Diabetes Mellitus Experimental/metabolismo , Dinoprostona/farmacologia , Útero/efeitos dos fármacos , Animais , Transporte Biológico/efeitos dos fármacos , Dinoprosta/farmacologia , Interações Medicamentosas , Feminino , Técnicas In Vitro , Insulina/farmacologia , Ovariectomia , Ratos , Ratos Wistar , Estreptozocina , Sacarose/metabolismo , Tromboxano B2/antagonistas & inibidores , Regulação para Cima , Útero/metabolismoRESUMO
The influx of 2,4-dichlorophenoxyacetic acid (2,4-D) into Chinese hamster ovary (CHO) cells was studied. The cells mainly took up but did not metabolize the undissociated form of the herbicide. The uptake of 2,4-D was carried out against a concentration gradient and was inhibited by sodium azide and dinitrophenol. The results presented here show that the herbicide influx was an active, energy dependent process. (Na+ + K+)ATPase does not seem to be involved because ouabain, an inhibitor of the enzyme, did not affect the 2,4-D uptake.
Assuntos
Ácido 2,4-Diclorofenoxiacético/farmacocinética , Herbicidas/farmacocinética , Ácido 2,4-Diclorofenoxiacético/toxicidade , 3-O-Metilglucose , Ácidos Aminoisobutíricos/farmacocinética , Animais , Azidas/farmacologia , Transporte Biológico Ativo/fisiologia , Células CHO , Cricetinae , Meios de Cultivo Condicionados , Dinitrofenóis/farmacologia , Inibidores Enzimáticos/farmacologia , Herbicidas/toxicidade , Concentração de Íons de Hidrogênio , Cinética , Metilglucosídeos/farmacocinética , Ouabaína/farmacologia , Fase S/efeitos dos fármacos , Azida Sódica , ATPase Trocadora de Sódio-Potássio/antagonistas & inibidoresRESUMO
The characteristics of the process by which contraction enhances glucose transport in the frog sartorius were studied. Electrical stimulation increased the permeability of muscles to 3-O-methylglucose (3-O-MeGlc), a nonmetabolizable glucose analogue, increasing efflux as well as uptake. Enhanced efflux was due to an increase in Vmax of the efflux process. A lactacidosis had no effect on basal 3-O-MeGlc efflux, and replacement of media Na+ with Li+ did not affect stimulation-induced uptake. Also, basal and stimulated uptake was not affected by 1 microM 12-O-tetradecanoylphorbol-13-acetate (TPA), a protein kinase C activator. Lastly, N-carbobenzoxy-glycyl-L-phenylalaninamide, which inhibits insulin-enhanced, but not basal, glucose uptake in adipocytes, inhibited both basal and stimulated 3-O-MeGlc fluxes in the frog sartorius. From these findings, we conclude: (1) contraction and exercise enhance glucose transport in muscle by increasing the number of transporters in the plasma membrane, or their turnover, by an unknown process; and (2) basal glucose transport of muscle, unlike that of adipocytes, can not be distinguished from stimulated transport on the basis of its insensitivity to N-carbobenzoxyglycyl-L-phenylalaninamide.