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M Camps

Publications and source records attributed to M Camps.

At least 73 records · Page 4Linked to original sources
PubMed1994

High and polarized expression of GLUT1 glucose transporters in epithelial cells from mammary gland: acute down-regulation of GLUT1 carriers by weaning.

During lactation, the mammary gland shows high metabolic activity, which is dependent at least in part on the availability of glucose. We have studied the regulation of glucose transporter expression in different types of cell in rat mammary gland during the reproductive cycle. Glucose transporter expression varied markedly in the mammary gland during ontogeny. Thus, GLUT1 protein expression increased progressively during pregnancy, reaching the highest levels during lactation. A peak of lactation, GLUT1 protein content, expressed per g issue, was greater in mammary gland than in GLUT1-enriched tissues such as rat brain. In contrast, GLUT4 showed a marked decrease during pregnancy and practically disappeared during lactation. Regardless of the developmental stage, GLUT4 was expressed in adipocytes but not in epithelial cells from mammary gland. On the other hand, GLUT1 was expressed in both cell types. The overall pattern of GLUT1 and GLUT4 expression during the reproductive cycle reflects differences in the cell composition of the mammary gland. Thus, whereas adipocytes predominate before pregnancy, epithelial cells are the main cell type in the mammary gland during late pregnancy and lactation. Immunofluorescence and immunoelectron microscopy indicated that GLUT1 was essentially localized to the basolateral domain of epithelial cells in the mammary gland at peak of lactation, and hardly any labeling was found in the luminal membrane of epithelial cells. GLUT1 expression was acutely regulated in epithelial cells from mammary gland. Thus, GLUT1 protein markedly decreased in lactating rats 24 h after abrupt weaning in the presence of a moderate decrease in GLUT1 mRNA levels. The effect of weaning on GLUT1 protein content was not due to the fall in the plasma concentration of PRL. Thus, bromocriptine treatment for 24 h decreased GLUT1 mRNA levels in the mammary gland, but did not alter the content of GLUT1 protein. Our results demonstrate 1) the existence of a high and polarized expression of GLUT1 glucose transporters in epithelial cells from mammary gland, and 2) that GLUT1 expression is acutely regulated at a posttranslational level by weaning; this is not mimicked by bromocriptine treatment, which rules out PRL as the regulatory factor involved in the effect.

Animals↗
PubMed1993

rBAT, related to L-cysteine transport, is localized to the microvilli of proximal straight tubules, and its expression is regulated in kidney by development.

We have recently isolated a renal cDNA clone (rBAT) that induces amino acid transport in oocytes either as a component or as a specific activator of a system bo,(+)-like transporter. (Bertran, J., Werner, A., Moore, M. L., Stange, G., Markovich, D., Biber, J., Testar, X., Zorzano, A., Palacín, M., and Murer, H. (1992) Proc. Natl. Acad. Sci. U. S. A. 89, 5601-5605. In order to obtain additional information on the rBAT protein, we have investigated the cellular localization of rBAT and its expression during development in rat kidney. A polyclonal antibody raised against rBAT recognizes a specific protein band of approximately 90 kDa, which is highly enriched in rat renal brush border membranes. Immunofluorescence and immunoelectron microscopy studies demonstrated that rBAT is expressed in the microvilli domain of S3 epithelial cells (i.e. straight tubules). The onset of rBAT mRNA expression in kidney was detected during late fetal life. In keeping with this, induction in oocytes of L-cystine uptake due to fetal rBAT-related mRNA was approximately 10% of the induction obtained with rBAT-related mRNA from adult kidneys. rBAT mRNA levels were low in early postnatal life, and only at the end of lactation did they increase steeply, attaining approximately 50% of adult values after weaning. rBAT protein was undetectable in total membrane preparations of kidneys from fetuses and early neonates, weakly detected during lactation, and represented < 15% of adult values after weaning. The postnatal expression of rBAT and its specific location in the microvilli of epithelial cells from the S3 segment of the proximal tubule coincide with postnatal maturation of cystine resorption and with the site of high affinity resorption of cysteine in kidney. This is consistent with the involvement of rBAT in a b(o,+)-like high-affinity resorption system for cysteine in the proximal straight tubule of the nephron.

Amino Acid Sequence↗
PubMed1993

Mutational analysis of phospholipase C-beta 2. Identification of regions required for membrane association and stimulation by guanine-nucleotide-binding protein beta gamma subunits.

Members of the beta isozyme subfamily of the phosphoinositide-specific phospholipases C (PLC beta) have recently been shown to be stimulated by both guanine-nucleotide-binding protein alpha and beta gamma subunits. The alpha subunits of the Gq class activate PLC beta isozymes in the order of PLC beta 1 > or = PLC beta 3 >> PLC beta 2, which is different from the order of PLC beta 3 > PLC beta 2 > PLC beta 1 for beta gamma subunit stimulation. The C-terminal region of PLC beta 1, in particular the sequence between Thr903 and Leu1142, has been shown to be involved in interacting with activated alpha q subunits and to contain a region required for efficient membrane association of PLC beta 1 [Park, D., Jhon, D.-Y., Lee, C.-W., Ryu, S. H. & Rhee, S. G. (1993) J. Biol. Chem. 268, 3710-3714, and Wu, D., Jiang, H., Katz, A. & Simon, M. I. (1993) J. Biol. Chem. 268, 3704-3709]. To examine the structure-function relationships of a PLC beta isozyme highly sensitive to beta gamma subunit stimulation, we have altered the cDNA of PLC beta 2 by site-directed mutagenesis and have examined the effects of these structural alterations on the functional properties of the mutant polypeptides. The results show that the C-terminal region of PLC beta 2 downstream of Phe818, which corresponds to Tyr816 of PLC beta 1, contains a region essential for membrane association, but is required neither for the interaction of PLC beta 2 with Ca2+ and the phospholipid substrate, nor for beta gamma subunit stimulation of PLC beta 2. These data suggest that PLC beta isozymes are activated by alpha q and beta gamma subunits via distinct domains.

Base Sequence↗
PubMed1993

A peptide corresponding to a potential polyphosphoinositide binding site of phospholipase C-beta 2 enhances its catalytic activity.

A peptide corresponding to a basic consensus amino acid motif present in both actin-binding proteins and phosphoinositide-specific phospholipases C was synthesized and its effect on the activity of a recombinant phospholipase C-beta 2 (PLC beta 2) expressed in baculovirus-infected insect cells was studied. The peptide markedly and specifically stimulated the activity of the enzyme. This stimulatory effect required a particular primary and/or secondary structure of the peptide and occurred without lowering the affinity of the enzyme for Ca2+. The function of the PLC beta 2 segment corresponding to the peptide might be to bind and offer the substrate to the catalytic domain of this enzyme in a more favorable configuration or, alternatively, to interact with a hypothetical inhibitory constraint.

Amino Acid Sequence↗
PubMed1993

Activation of phosphatidylinositol lipid-specific phospholipase C-beta 3 by G-protein beta gamma subunits.

A novel member of the inositol lipid-specific phospholipase C family, PtdIns-PLC beta 3, is shown to be activated by beta gamma subunits of the heterotrimeric GTP-binding protein, transducin. The activation is a direct effect since it is observed with the purified proteins. Furthermore, the activation is blocked by the GDP-liganded alpha subunit of transducin, confirming that the effect is due to free beta gamma subunits. The implications with respect to receptor-PtdIns-PLC coupling are discussed.

Animals↗
PubMed1993

Protein phosphatases in higher plants: multiplicity of type 2A phosphatases in Arabidopsis thaliana.

Two DNA fragments, AP-1 and AP-2, encoding amino acid sequences closely related to Ser/Thr protein phosphatases were amplified from Arabidopsis thaliana genomic DNA. Fragment AP-1 was used to screen A. thaliana cDNA libraries and several positive clones were isolated. Clones EP8a and EP14a were sequenced and found to encode almost identical proteins (97% identity). Both proteins are 306 amino acids in length and are very similar (79-80% identity) to the mammalian isotypes of the catalytic subunit of protein phosphatase 2A. Therefore, they have been designated PP2A-1 and PP2A-2. A third cDNA clone, EP7, was isolated and sequenced. The polypeptide encoded (308 amino acids, lacking the initial Met codon) is 80% identical with human phosphatases 2A and was named PP2A-3. The PP2A-3 protein is extremely similar (95% identity) to the predicted protein from a cDNA clone previously found in Brassica napus. Southern blot analysis of genomic DNA using AP-1 and AP-2 probes, as well as probes derived from clones EP7, EP8a and EP14a strongly indicates that at least 6 genes closely related to type 2A phosphatases are present in the genome of A. thaliana. Northern blot analysis using the same set of probes demonstrates that, at the seedling stage, the mRNA levels for PP2A-1, PP2A-3 and the gene containing the AP-1 sequence are much higher than those of PP2A-2 and AP-2. These results demonstrate that a multiplicity of type 2A phosphatases might be differentially expressed in higher plants.

Amino Acid Sequence↗
PubMed1993

Effect of benzyl succinate on insulin receptor function and insulin action in skeletal muscle: further evidence for a lack of spare high-affinity insulin receptors.

Benzyl succinate inhibited insulin binding and tyrosine receptor kinase in a concentration-dependent manner in the partially purified insulin receptor preparation from rat skeletal muscle. Benzyl succinate lowered the apparent number of high-affinity insulin binding sites. We have made use of the inhibitory effect of benzyl succinate to investigate the possible presence of spare high-affinity insulin receptors in muscle. Benzyl succinate inhibited the effect of a supramaximal concentration of insulin on 3-O-methylglucose uptake, 2-(methylamino)isobutyric acid uptake and lactate production by the incubated muscle. Furthermore, the inhibitory effect of benzyl succinate on insulin binding in vitro closely correlated with its inhibitory effect on insulin action in vivo. These findings suggest the absence of spare high-affinity insulin receptors in skeletal muscle. In contrast to data obtained in skeletal muscle, benzyl succinate did not affect the maximally insulin-stimulated glucose transport, although it caused a marked decrease in insulin sensitivity in isolated rat adipocytes, for which the existence of spare insulin receptors is well documented.

3-O-Methylglucose↗
PubMed1993

Effect of age and cinnarizine treatment on brain dopamine receptors.

The density and distribution of dopamine D1 and D2 receptors visualized by in vitro autoradiography were investigated in adult and senescent BL C57 mice. A significant decrease was observed in regions of the basal ganglia of senescent animals, which was more pronounced for the D1 subtype. Chronic treatment with cinnarizine, an organic Ca2+ channel antagonist, alters both D1 and D2 receptor densities, with a higher sensitivity of the D1 subtype. These results could indicate that the interactions between dopamine receptor subtypes may be necessary for the full expression of behavioral events mediated by the D2 receptors.

Aging↗
PubMed1992

Isozyme-selective stimulation of phospholipase C-beta 2 by G protein beta gamma-subunits.

Hydrolysis by phospholipase C (PLC) of phosphatidylinositol 4,5-bisphosphate is a key mechanism by which many extracellular signalling molecules regulate functions of their target cells. At least eight distinct isozymes of PLC are recognized in mammalian cells. Receptor-controlled PLC is often regulated by G proteins, which can be modified by pertussis toxin in some cells but not in others. In the latter cells, PLC-beta 1, but not PLC-gamma 1 or PLC-delta 1, may be activated by members of the alpha q-subfamily of the G protein alpha-subunits. An unidentified PLC in soluble fractions of cultured human HL-60 granulocytes is specifically stimulated by G protein beta gamma subunits purified from retina and brain. Identification of a second PLC-beta complementary DNA (PLC-beta 2) in an HL-60 cell cDNA library prompted us to investigate the effect of purified G protein beta gamma subunits on the activities of PLC-beta 1 and PLC-beta 2 transiently expressed in cultured mammalian cells. We report here that PLC-beta 1 and PLC-beta 2 were stimulated by free beta gamma subunits and that PLC-beta 2 was the most sensitive to beta gamma stimulation. Thus stimulation of PLC by beta gamma subunits is isozyme-selective and PLC-beta 2 is a prime target of beta gamma stimulation. Activation of PLC-beta 2 by beta gamma subunits may be an important mechanism by which pertussis toxin-sensitive G proteins stimulate PLC.

Animals↗
PubMed1992

Expression, characterization and purification of soluble G-protein beta gamma dimers composed of defined subunits in baculovirus-infected insect cells.

Recombinant beta 1 gamma 2 dimers of signal-transducing guanine nucleotide-binding proteins (G-proteins) carrying a mutation known to block isoprenylation of the gamma 2 subunit were expressed as a soluble protein in baculovirus-infected insect cells. The soluble beta gamma dimer was analyzed by sucrose density gradient centrifugation and purified to near homogeneity in the absence of detergents. The sedimentation velocity studies gave an S20,w value of 4.1 +/- 0.4 S. The two subunits segregated as a dimer upon sucrose density gradient centrifugation and purification by sequential ion exchange and hydroxylapatite chromatography. The results show that baculovirus-infected insect cells can be employed for high level production of pure G-protein beta gamma dimers suitable for functional and structural characterization.

Amino Acid Sequence↗
PubMed1992

Stimulation of phospholipase C by a mutationally activated G protein alpha 16 subunit.

Alpha 16, a member of the alpha q subfamily of G protein alpha subunits, was recently identified in human hematopoietic cells. In order to elucidate the function of this novel alpha subunit, we cloned and mutagenized its cDNA to obtain a constitutively active protein. COS-1 cells were transfected with both wild-type and mutant cDNAs. Expression was confirmed by immunoblotting using a rabbit antiserum raised against the C-terminal decapeptide of alpha 16. The constitutively activated mutant alpha 16-R186C caused a two-fold increase in the formation of inositol trisphosphate in intact COS-1 cells, while the wild-type alpha 16 subunit had no effect. We conclude that alpha 16 is involved in coupling cell surface receptors of human hematopoietic cells to stimulation of phospholipase C.

Animals↗
PubMed1992

Evidence for the lack of spare high-affinity insulin receptors in skeletal muscle.

In this study, the relationship between the concentration of extracellular insulin, insulin binding and insulin action was evaluated in skeletal muscle. Initially we investigated the dose-response relationship of insulin action using three different experimental models that are responsive to insulin, i.e. the isolated perfused rat hindquarter, incubated strips of soleus muscle, and insulin receptors partially affinity-purified from skeletal muscle. We selected as insulin-sensitive parameters glucose uptake in the perfused hindquarter, lactate production in the incubated muscle preparation, and tyrosine receptor kinase activity in the purified receptor preparation. Our results showed that the dose-response curves obtained in the perfused hindquarter and in the incubated muscle were superimposable. In contrast, the dose-response curve for insulin-stimulated receptor tyrosine kinase activity in partially purified receptors was displaced to the left compared with the curves obtained in the perfused hindquarter and in the incubated muscle. The differences between the dose-response curve for receptor tyrosine kinase and those for glucose uptake and lactate production were not explained by a substantial insulin concentration gradient between medium and interstitial space. Thus the medium/interstitial insulin concentration ratio, when assayed in the incubated intact muscle at 5 degrees C, was close to 1. We also compared the dose-response curve of insulin-stimulated receptor tyrosine kinase with the pattern of insulin-binding-site occupancy. The curve of insulin-stimulated receptor kinase activity fitted closely with the occupancy of high-affinity binding sites. In summary, assuming that the estimation of the medium/interstitial insulin concentration ratio obtained at 5 degrees C reflects the actual ratio under more physiological conditions, our results suggest that maximal insulin action is obtained in skeletal muscle at insulin concentrations which do allow full occupancy of high-affinity binding sites. Therefore our data provide evidence for a lack of spare high-affinity insulin receptors in skeletal muscle.

Animals↗
PubMed1992

Stimulation of phospholipase C by guanine-nucleotide-binding protein beta gamma subunits.

We have previously shown that soluble fractions obtained from human HL-60 granulocytes contain a phospholipase C which is markedly stimulated by the stable GTP analogue guanosine 5'-[3-O-thio]triphosphate (Camps, M., Hou, C., Jakobs, K. H. and Gierschik, P. (1990) Biochem. J. 271, 743-748]. To investigate whether this stimulation was due to a soluble alpha subunit of a heterotrimeric guanine-nucleotide-binding protein or a soluble low-molecular-mass GTP-binding protein, we have examined the effect of purified guanine-nucleotide-binding protein beta gamma dimers on the phospholipase-C-mediated formation of inositol phosphates by HL-60 cytosol. We found that beta gamma subunits, purified from bovine retinal transducin (beta gamma t), markedly stimulated the hydrolysis of phosphatidylinositol 4,5-bisphosphate by this phospholipase C preparation. The stimulation of phospholipase C by beta gamma t was not secondary to a phospholipase-A2-mediated generation of arachidonic acid, was prevented by the GDP-liganded transducin alpha subunit and was additive to activation of phospholipase C by guanosine 5'-[3-O-thio]triphosphate. Beta gamma t also stimulated soluble phospholipase C from human and bovine peripheral neutrophils, as well as membrane-bound, detergent-solubilized phospholipase C from HL-60 cells. Stimulation of soluble HL-60 phospholipase C was not restricted to beta gamma t, but was also observed with highly purified beta gamma subunits from bovine brain. Fractionation of HL-60 cytosol by anion-exchange chromatography revealed the existence of at least two distinct forms of phospholipase C in HL-60 granulocytes. Only one of these forms was sensitive to stimulation by beta gamma t, demonstrating that stimulation of phospholipase C by beta gamma subunits is isozyme specific. Taken together, our results suggest that guanine-nucleotide-binding protein beta gamma subunits may play an important and active role in mediating the stimulation of phospholipase C by heterotrimeric guanine-nucleotide-binding proteins.

Animals↗
PubMed1992

Vanadate stimulates system A amino acid transport activity in skeletal muscle. Evidence for the involvement of intracellular pH as a mediator of vanadate action.

Sodium orthovanadate caused a 2-fold stimulation of system A transport activity in soleus muscle, as assessed by the uptake of the nonmetabolizable analog 2-(methylamino)isobutyric acid (MeAIB). The effect of vanadate on system A was rapid, concentration-dependent and was characterized by an increased Vmax without modification of Km for MeAIB. Under these conditions, vanadate also activated 3-O-methylglucose uptake and lactate production. The effects of vanadate on muscle metabolism showed a complex interaction with the effects of insulin. Thus, the stimulatory effects of vanadate and insulin on MeAIB and 3-O-methylglucose uptake were not additive; however, the effects of insulin and vanadate on lactate production were additive. In spite of the lack of additivity, insulin- and vanadate-induced stimulation of system A differed in their sensitivity to gramicidin D, being the vanadate effect more susceptible to inhibition by gramicidin D than the insulin effect. System A transport activity shows a dependence on pH, and recent results suggest the presence of critical histidine residues on the A carrier that may be responsible for its pH dependence (Bertran, J., Roca, A., Pola, E., Testar, X., Zorzano, A. & Palacín, M. (1991) J. Biol. Chem. 266, 798-802). In this regard, a rise in extracellular pH led to a substantial activation of system A. Furthermore, lowering of muscle intracellular pH induced by ethylisopropylamiloride (EIPA), a specific inhibitor of sodium/proton exchange activity, led to inhibition of system A. This suggests that critical histidine residues are present in an intracellular localization on the A carrier. Furthermore, the rate of muscle glycolysis was also altered in response to a rise in extracellular pH or to EIPA treatment. Regarding the mechanisms involved in vanadate action, vanadate treatment in the incubated soleus muscle did not cause any significant stimulation of tyrosine kinase activity after partial purification of muscle insulin receptors. On the other hand, vanadate but not insulin caused a substantial increase in muscle intracellular pH as assessed by 5,5'-dimethyloxazolidine-2,4-dione equilibrium. This effect of vanadate on intracellular pH was not due to activation of the sodium/proton exchanger, since it was not blocked by EIPA. Based on these findings, we suggest that alkalinization of muscle intracellular pH might mediate the effects of vanadate on system A and on glycolysis.

Amiloride↗
PubMed1992

Effect of diabetes and fasting on GLUT-4 (muscle/fat) glucose-transporter expression in insulin-sensitive tissues. Heterogeneous response in heart, red and white muscle.

1. GLUT-4 glucose-transporter protein and mRNA levels were assessed in heart, red muscle and white muscle, as well as in brown and white adipose tissue from 7-day streptozotocin-induced diabetic and 48 h-fasted rats. 2. In agreement with previous data, white adipose tissue showed a substantial decrease in GLUT-4 mRNA and protein levels in response to both diabetes and fasting. Similarly, GLUT-4 mRNA and protein markedly decreased in brown adipose tissue in both insulinopenic conditions. 3. Under control conditions, the level of expression of GLUT-4 protein content differed substantially in heart, red and white skeletal muscle. Thus GLUT-4 protein was maximal in heart, and red muscle had a greater GLUT-4 content compared with white muscle. In spite of the large differences in GLUT-4 protein content, GLUT-4 mRNA levels were equivalent in heart and red skeletal muscle. 4. In heart, GLUT-4 mRNA decreased to a greater extent than GLUT-4 protein in response to diabetes and fasting. In contrast, red muscle showed a greater decrease in GLUT-4 protein than in mRNA in response to diabetes or fasting, and in fact no decrease in GLUT-4 mRNA content was detectable in fasting. On the other hand, preparations of white skeletal muscle showed a substantial increase in GLUT-4 mRNA under both insulinopenic conditions, and that was concomitant to either a modest decrease in GLUT-4 protein in diabetes or to no change in fasting. 5. These results indicate that (a) the effects of diabetes and fasting are almost identical and lead to changes in GLUT-4 expression that are tissue-specific, (b) white adipose tissue, brown adipose tissue and heart respond similarly to insulin deficiency by decreasing GLUT-4 mRNA to a larger extent than GLUT-4 protein, and (c) red and white skeletal muscle respond to insulinopenic conditions in a heterogeneous manner which is characterized by enhanced GLUT-4 mRNA/protein ratios.

Adipose Tissue↗
PubMed1992

Inhibitors such as staurosporine, H-7 or polymyxin B cannot be used in skeletal muscle to prove the role of protein kinase C on insulin action.

The precise role of protein kinase C in insulin action in skeletal muscle is not well defined. Based on the fact that inhibitors of protein kinase C block some insulin effects, it has been concluded that some of the biological actions of insulin are mediated via protein kinase C. In this study, we present evidence that inhibitors of protein kinase C such as staurosporine, H-7 or polymyxin B cannot be used to ascertain the role of protein kinase C in skeletal muscle. This is based on the following experimental evidences: a) staurosporine, H-7 and polymyxin B markedly block in muscle the effect of insulin on System A transport activity; however, this effect of insulin is not mimicked in muscle by TPA-induced stimulation of protein kinase C, b) H-7 and polymyxin B block insulin action on System A transport activity in an additive manner to the inhibitory effect of phorbol esters, c) staurosporine, H-7 and polymyxin B block the effect of insulin on lactate production, a process that is activated by insulin and TPA in an additive fashion, and d) staurosporine completely blocks the tyrosine kinase activity of insulin receptors partially purified from rat skeletal muscle.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1992

Developmental regulation of GLUT-1 (erythroid/Hep G2) and GLUT-4 (muscle/fat) glucose transporter expression in rat heart, skeletal muscle, and brown adipose tissue.

The expression of GLUT-1 (erythroid/Hep G2) and GLUT-4 (muscle/fat) glucose transporters was assessed during development in rat heart, skeletal muscle, and brown adipose tissue. GLUT-4 protein expression was detectable in fetal heart by day 21 of pregnancy; it increased progressively after birth, attaining levels close to those of adults at day 15 post natal. In contrast, GLUT-4 messenger RNA (mRNA) was already present in hearts from 17 day-old fetuses. GLUT-4 mRNA stayed low during early postnatal life in heart and brown adipose tissue and only increased after day 10 post natal. The expression pattern for GLUT-4 protein in skeletal muscle during development was comparable to that observed in heart. In contrast to heart and skeletal muscle, GLUT-4 protein in brown adipose tissue was detected in high levels (30% of adult) during late fetal life. During fetal life, GLUT-1 presented a very high expression level in brown adipose tissue, heart, and skeletal muscle. Soon after birth, GLUT-1 protein diminished progressively, attaining adult levels at day 10 in heart and skeletal muscle. GLUT-1 mRNA levels in heart followed a similar pattern to the GLUT-1 protein, being very high during fetal life and decreasing early in post natal life. GLUT-1 protein showed a complex pattern in brown adipose tissue: fetal levels were high, decreased after birth, and increased subsequently in post natal life, reaching a peak by day 9. Progesterone-induced postmaturity protected against the decrease in GLUT-1 protein associated with post natal life in skeletal muscle and brown adipose tissue. However, GLUT-4 induction was not blocked by postmaturity in any of the tissues subjected to study. These results indicate that: 1) during fetal and early post natal life, GLUT-1 is a predominant glucose transporter isotype expressed in heart, skeletal muscle, and brown adipose tissue; 2) during early post natal life there is a generalized GLUT-1 repression; 3) during development, there is a close correlation between protein and mRNA levels for GLUT-1, and therefore regulation at a pretranslational level plays a major regulatory role; 4) the onset of GLUT-4 protein induction occurs between days 20-21 of fetal life; based on data obtained in rat heart and brown adipose tissue, there is a dissociation during development between mRNA and protein levels for GLUT-4, suggesting modifications at translational or posttranslational steps; and 5) postmaturity blocks the decrease in GLUT-1 expression but not the induction of GLUT-4, observed soon after birth.(ABSTRACT TRUNCATED AT 400 WORDS)

Adipose Tissue, Brown↗