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B Thorens

Publications and source records attributed to B Thorens.

At least 19 recordsLinked to original sources
PubMed1992

Expression cloning of the pancreatic beta cell receptor for the gluco-incretin hormone glucagon-like peptide 1.

Glucagon-like peptide 1 (GLP-1) is a hormone derived from the preproglucagon molecule and is secreted by intestinal L cells. It is the most potent stimulator of glucose-induced insulin secretion and also suppresses in vivo acid secretion by gastric glands. A cDNA for the GLP-1 receptor was isolated by transient expression of a rat pancreatic islet cDNA library into COS cells; this was followed by binding of radiolabeled GLP-1 and screening by photographic emulsion autoradiography. The receptor transfected into COS cells binds GLP-1 with high affinity and is coupled to activation of adenylate cyclase. The receptor binds specifically GLP-1 and does not bind peptides of related structure and similar function, such as glucagon, gastric inhibitory peptide, vasoactive intestinal peptide, or secretin. The receptor is 463 amino acids long and contains seven transmembrane domains. Sequence homology is found only with the receptors for secretin, calcitonin, and parathyroid hormone, which form a newly characterized family of G-coupled receptors.

Animals↗
PubMed1992

Glucose transporter isotypes switch in T-antigen-transformed pancreatic beta cells growing in culture and in mice.

High-level expression of the low-Km glucose transporter isoform GLUT-1 is characteristic of many cultured tumor and oncogene-transformed cells. In this study, we tested whether induction of GLUT-1 occurs in tumors in vivo. Normal mouse beta islet cells express the high-Km (approximately 20 mM) glucose transporter isoform GLUT-2 but not the low-Km (1 to 3 mM) GLUT-1. In contrast, a beta cell line derived from an insulinoma arising in a transgenic mouse harboring an insulin-promoted simian virus 40 T-antigen oncogene (beta TC3) expressed very low levels of GLUT-2 but high levels of GLUT-1. GLUT-1 protein was not detectable on the plasma membrane of islets or tumors of the transgenic mice but was induced in high amounts when the tumor-derived beta TC3 cells were grown in tissue culture. GLUT-1 expression in secondary tumors formed after injection of beta TC3 cells into mice was reduced. Thus, high-level expression of GLUT-1 in these tumor cells is characteristic of culture conditions and is not induced by the oncogenic transformation; indeed, overnight culture of normal pancreatic islets causes induction of GLUT-1. We also investigated the relationship between expression of the different glucose transporter isoforms by islet and tumor cells and induction of insulin secretion by glucose. Prehyperplastic transgenic islet cells that expressed normal levels of GLUT-2 and no detectable GLUT-1 exhibited an increased sensitivity to glucose, as evidenced by maximal insulin secretion at lower glucose concentrations, compared with that exhibited by normal islets. Further, hyperplastic islets and primary and secondary tumors expressed low levels of GLUT-2 and no detectable GLUT-1 on the plasma membrane; these cells exhibited high basal insulin secretion and responded poorly to an increase in extracellular glucose. Thus, abnormal glucose-induced secretion of insulin in prehyperplastic islets in mice was independent of changes in GLUT-2 expression and did not require induction of GLUT-1 expression.

Animals↗
PubMed1992

The loss of GLUT2 expression by glucose-unresponsive beta cells of db/db mice is reversible and is induced by the diabetic environment.

Glucose-induced insulin secretion by beta cells of diabetic db/db mice was studied by a pancreas perfusion technique, and the levels of GLUT2 protein in pancreatic islets were assessed by immunofluorescence microscopy and protein blot analysis. Beta cells from diabetic mice had a high basal rate of insulin secretion; they did not respond to glucose stimulation but displayed a normal secretory response to arginine. At the same time, GLUT2 expression by db/db islets was lost whereas beta cells from nondiabetic db/+ mice expressed high levels of this transporter. GLUT2 levels in liver or kidney of diabetic mice were, however, mostly unaltered. Transplanting islets from db/db mice under the kidney capsule of db/+ mice restored normal GLUT2 levels. Conversely, transplantation of db/+ islets into db/db mice induced the disappearance of GLUT2 expression. When islets from db/+ mice were transplanted under the kidney capsule of streptozocin-diabetic mice, the immunodetection of GLUT2 also disappeared. We conclude that: (a) GLUT2 expression is decreased in glucose-unresponsive beta cells from db/db mice; (b) the decreased expression of GLUT2 is reversible; (c) the loss of GLUT2 expression is induced by the diabetic environment of db/db and streptozocin-induced diabetic mice. These observations together with previously published data suggest that a factor different from glucose or insulin regulates the beta cell expression of GLUT2.

Animals↗
PubMed1992

Developmental expression and cellular localization of glucose transporter molecules during mouse preimplantation development.

Two general mechanisms mediate glucose transport, one is a sodium-coupled glucose transporter found in the apical border of intestinal and kidney epithelia, while the other is a sodium-independent transport system. Of the latter, several facilitated transporters have been identified, including GLUT1 (erythrocyte/brain), GLUT2 (liver) and GLUT4 (adipose/muscle) isoforms. In this study, we used Western-blot analysis and high resolution immunoelectron microscopy (IEM) to investigate the stage-related expression and cellular localization of GLUT1, 2 and 4. The Western blot results demonstrate that GLUT1 is detectable in the oocyte and throughout preimplantation development. GLUT2 isoforms were not detectable until the blastocyst stage, while the GLUT4 isoform was undetectable in the oocyte through blastocyst stages. The present findings confirm previous studies at the molecular level which demonstrated that mRNAs encoding the same GLUT isoforms are detectable at corresponding developmental stages. GLUT1 and GLUT2 display different cellular distributions at the blastocyst stage as shown by IEM studies. GLUT1 has a widespread distribution in both trophectoderm and inner cell mass cells, while GLUT2 is located on trophectoderm membranes facing the blastocyst cavity. This observation suggests a different functional significance for these isoforms during mouse preimplantation development.

Animals↗
PubMed1992

Recovery of glucose-induced insulin secretion in a rat model of NIDDM is not accompanied by return of the B-cell GLUT2 glucose transporter.

The NSTZ rat model combines loss of glucose-induced insulin secretion with a reduced amount of the high Km B-cell glucose transporter, GLUT2. The purpose of this study was to determine whether the restoration of glucose-induced insulin secretion was paralleled by an increase of GLUT2. Rats injected at 2 days of age with 90 mg/kg STZ were studied at 8-13 wk of age. Insulin secretion was assessed in the isolated perfused pancreas with 16.7 mM glucose preceded by 40 min of 0 or 5.5 mM glucose. In control rats, 16.7 mM glucose caused the same large biphasic insulin response whether preceded by 0 or 5.5 mM glucose. In NSTZ rats, after 5.5 mM glucose, 16.7 mM glucose elicited virtually no rise in insulin release. In contrast, after 0 mM glucose, a large insulin response to the glucose challenge occurred that was equal to that of the control groups when the differences in B-cell mass were taken into account. However, the dose-response curve for glucose-induced insulin secretion was shifted to the left, and no second phase of insulin secretion was observed. GLUT2 was assessed after the perfusions by indirect immunofluorescence with anti-GLUT2 antisera. Both control groups showed homogenous staining in all B-cells. NSTZ rats perfused with 5.5 mM glucose had a marked diminution in GLUT2 staining. We observed no increase in GLUT2 staining in the NSTZ rats perfused with 0 mM glucose.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

[Occupational bronchitis].

Industrial bronchitis is defined as a chronic bronchitis due to prolonged exposure to polluted air at the professional workplace. Up until the nineteen eighties, its proper existence was open to controversy, because outside professional factors, such as tobacco, were considered as predominant causes. However, the most recent epidemiological studies have shown that exposure to dust, in conjunction or not with fumes and gases, was responsible for chronic obstructive syndromes. Bronchitis observed in silicotic patients is an interesting example. On the other hand, in other occupations, such as soldering, in which only gases and fumes are inhaled, the risk of chronic obstructive bronchitis is minimal. Due to the threshold limit values enforced by law since many years in Switzerland, the probability of industrial bronchitis is low; therefore the proportional responsibility of tobacco as cause of pulmonary obstruction is increased and justifies preventive effort also in this field.

Air Pollutants, Occupational↗
PubMed1991

Expression of facilitative glucose transporter in rat liver and choroid plexus. A histochemical study in native cryostat sections.

Two isoforms of facilitative glucose transporters (GLUT), namely the erythroid/brain-type GLUT 1 and the liver-type GLUT 2, were demonstrated in native cryostat sections of normal rat liver and brain by immunofluorescence and a very sensitive immunoalkaline phosphatase reaction. Fixation with 0.1% alcoholic periodic acid resulted in an excellent localization of GLUT 2 in liver and GLUT 1 in brain. GLUT 1 in liver, however, could successfully be demonstrated after fixation with 1% alcoholic formaldehyde. GLUT 2 occurred in all hepatocytes as a basolateral membrane protein with a gradient of high expression in the periportal area and a lower one in the perivenous part. The first layer of hepatocytes adjacent to the hepatic vein coexpressed GLUT 1. In addition, GLUT 1 could be detected in the smooth muscle layer of the portal vein and in the apical and lateral plasma membrane of the bile duct epithelium. In brain, GLUT 1 showed a high expression in the microvessels, the ependyma and in the basal plasma membrane of choroid plexus epithelial cells. The blood capillaries associated with the choroidal epithelium were, however, negative for GLUT 1. The importance of the new findings in this study for the physiological role of the respective facilitative glucose transport proteins is discussed.

Alkaline Phosphatase↗
PubMed1991

Evidence from oocyte expression that the erythrocyte water channel is distinct from band 3 and the glucose transporter.

It has been proposed that the mercurial-sensitive water transporter in mammalian erythrocytes is the anion exchanger band 3 (AE1) and/or the glucose transporter, band 4.5 (GLUT1). Using a functional assay for water channel expression in Xenopus oocytes (Zhang, R., K. A. Logee, and A. S. Verkman. 1990. J. Biol. Chem. 265:15375-15378), we compared osmotic water permeability (Pf) of oocytes injected with water, reticulocyte mRNA, AE1 mRNA, and GLUT1 mRNA. Injection of oocytes with 5-50 ng of in vitro-transcribed AE1 mRNA had no effect on Pf, but increased trans-stimulated 36Cl uptake greater than fourfold in a dinitro-disulfonic stilbene (DNDS)-inhibitable manner. Injection with 1-50 ng of in vitro-transcribed GLUT1 mRNA increased 3H-methylglucose uptake greater than 15-fold in a cytochalasin B-sensitive manner and increased Pf from (3.7 +/- 0.4) x 10(-4) cm/s (SE, n = 16, 10 degrees C) in water-injected oocytes up to (13 +/- 1) x 10(-4) cm/s (n = 18). Both the increments in sugar and water transport were inhibited by cytochalasin B (25 microM) and phloretin (0.2 mM); neither was inhibited by 0.3 mM HgCl2. In oocytes injected with 50 ng of rabbit reticulocyte mRNA, the Pf of (18 +/- 2) x 10(-4) cm/s (n = 18) was reduced to (4.0 +/- 0.6) x 10(-4) cm/s (n = 10) by HgCl2, but was not inhibited by DNDS (0.4 mM), cytochalasin B or phloretin. Coinjection of reticulocyte mRNA with antisense oligodeoxyribonucleotides against AE1 or GLUT1 did not affect Pf, but inhibited completely the incremental uptake of 36Cl or 3H-methylglucose, respectively. Expression of size-fractionated mRNA from reticulocyte gave a 2-2.5-kb size for water channel mRNA, less than the 4-4.5-kb size for the Cl transporter. These results provide evidence that facilitated water transport in erythrocytes is mediated not by bands 3 or 4.5, but by distinct water transport protein(s).

Animals↗
PubMed1991

Glucose transporter gene expression in early mouse embryos.

The glucose transporter (GLUT) isoforms responsible for glucose uptake in early mouse embryos have been identified. GLUT 1, the isoform present in nearly every tissue examined including adult brain and erythrocytes, is expressed throughout preimplantation development. GLUT 2, which is normally present in adult liver, kidney, intestine and pancreatic beta cells is expressed from the 8-cell stage onward. GLUT 4, an insulin-recruitable isoform, which is expressed in adult fat and muscle, is not expressed at any stage of preimplantation development or in early postimplantation stage embryos. Genetic mapping studies of glucose transporters in the mouse show that Glut-1 is located on chromosome 4, Glut-2 on chromosome 3, Glut-3 on chromosome 6, and Glut-4 on chromosome 11.

Amino Acid Sequence↗
PubMed1990

The high Km glucose transporter of islets of Langerhans is functionally similar to the low affinity transporter of liver and has an identical primary sequence.

The liver has been shown to contain a facilitated diffusion glucose transporter with high Km for glucose that is structurally distinct from the low Km glucose transporters found in most other tissues. We find that 3-O-methyl glucose is greater than 90% equilibrated across dispersed islet cells within 60 s, consistent with a facilitated diffusion transport mechanism. L-Glucose uptake was minimal throughout the time course, indicating stereospecificity. Measurement of glucose transport over a range of 3-O-methyl glucose concentrations from 0.05 to 60 mM revealed the presence of a component of glucose transport with an apparent Km of 17 mM, a value essentially identical to that previously reported for liver. Interestingly, a second component of glucose transport was also observed with an apparent Km of 1.4 mM, as has been reported for other tissues such as erythrocytes that are known to contain the "HepG2" or "erythroid/brain" type glucose transporter. Further evidence for the existence of two transport components is provided by the observation that a low concentration of cytochalasin B (0.4 microM) completely inhibits the low Km transport activity but has no effect on the high Km transporter. The kinetic similarity of high Km glucose transport in liver and islets is readily understood in light of our structural analysis. Sequence analysis of cDNA clones indicates that the liver and islet glucose transporters have identical sequences and, thus, are the products of the same gene.

3-O-Methylglucose↗
PubMed1990

Reduced expression of the liver/beta-cell glucose transporter isoform in glucose-insensitive pancreatic beta cells of diabetic rats.

Rats injected with a single dose of streptozocin at 2 days of age develop non-insulin-dependent diabetes 6 weeks later. The pancreatic beta islet cells of these diabetic rats display a loss of glucose-induced insulin secretion while maintaining sensitivity to other secretagogues such as arginine. We analyzed the level of expression of the liver/beta-cell glucose transporter isoform in diabetic islets by immunofluorescence staining of pancreas sections and by Western blotting of islet lysates. Islets from diabetic animals have a reduced expression of this beta-cell-specific glucose transporter isoform and the extent of reduction is correlated with the severity of hyperglycemia. In contrast, expression of this transporter isoform in liver is minimally modified by the diabetes. Thus a decreased expression of the liver/beta-cell glucose transporter isoform in beta cells is associated with the impaired glucose sensing characteristic of diabetic islets; our data suggest that this glucose transporter may be part of the beta-cell glucose sensor.

Animals↗
PubMed1990

Liver glucose transporter: a basolateral protein in hepatocytes and intestine and kidney cells.

The "liver" isoform of the facilitated diffusion glucose transporter is expressed predominantly in liver, intestine, kidney, and pancreatic islet beta-cells. The apparent molecular mass of the transporter in liver, kidney, and intestine is different, as detected by Western blot analysis of membrane proteins using antipeptide antibodies. However, as assessed by Northern blot analysis and molecular cloning, the same mRNA is expressed in these tissues, indicating that there are tissue-specific posttranslational modifications of the same transporter polypeptide. As determined by immunofluorescence analysis on frozen tissue sections, the liver glucose transporter is present on the sinusoidal membrane of hepatocytes, on the basolateral membrane of fully differentiated absorptive intestine epithelial cells, and on the basolateral membrane of proximal tubule cells of the kidney nephron. This localization is consistent with the involvement of the liver glucose transporter in several key steps of glucose metabolism: glucose uptake and release by the liver and absorption or reabsorption by epithelial cells of the intestine and kidney, respectively.

Animals↗
PubMed1990

Differential localization of two glucose transporter isoforms in rat kidney.

The localization of two glucose transporter isoforms was mapped in the rat kidney: the high-Michaelis constant (Km; 15-20 mM) low-affinity "liver" transporter and the low-Km (1-2 mM) high-affinity "erythroid/brain" transporter. Both are basolateral membrane proteins, but the liver transporter was present exclusively in the S1 part of the proximal tubule, whereas the erythroid/brain transporter was expressed at variable levels in different nephron segments. Staining intensity was low in the straight proximal tubule (S3), intermediate in the medullary thin and thick ascending limbs, and highest in connecting segments and collecting ducts. In the collecting duct, the erythroid/brain glucose transporter was expressed at the highest level in intercalated cells; less was present in principal cells. In the papilla, only intercalated cells expressed this transporter isoform. These results suggest specific involvements of each transporter isoform in transepithelial glucose reabsorption by different segments of the proximal tubule. They also indicate that while the liver glucose transporter is present in gluconeogenic cells, there is a good correlation between the level of expression of the erythroid/brain glucose transporter and the glycolytic activity of the different nephron segments.

Animals↗
PubMed1990

Restricted expression of the erythroid/brain glucose transporter isoform to perivenous hepatocytes in rats. Modulation by glucose.

The "erythroid/brain" glucose transporter (GT) isoform is expressed only in a subset of hepatocytes, those forming the first row around the terminal hepatic venules, while the "liver" GT is expressed in all hepatocytes. After 3 d of starvation, a three- to fourfold elevation of expression of the erythroid/brain GT mRNA and protein is detected in the liver as a whole; this correlates with the expression of this GT in more hepatocytes, those forming the first three to four rows around the hepatic venules. Starvation-dependent expression of the erythroid/brain GT on the plasma membrane of these additional hepatocytes is lost within 3 h of glucose refeeding; however, by immunoblotting we show that the protein is still present. Its loss from the surface is possibly explained by internalization.

Animals↗
PubMed1990

Reduced beta-cell glucose transporter in new onset diabetic BB rats.

Previous studies from our laboratories have suggested a defect in glucose transport in islets isolated from BB rats on the first day of overt diabetes. To quantitate by immunostaining the glucose transporter of beta-cells (GLUT-2) before and at the onset of autoimmune diabetes we employed an antibody to its COOH-terminal octapeptide. On the first day of overt diabetes, defined as the day the daily blood glucose first reached 200 mg/dl, the volume density ratio of GLUT-2-positive to insulin-positive beta-cells was only 0.48 +/- 0.06, compared to 0.91 +/- 0.02 in age-matched nondiabetic diabetes-resistant controls (P less than 0.001). In age-matched nondiabetic diabetes-prone rats, most of which would have become diabetic, the ratio was 0.85 +/- 0.02, also less than the controls (P less than 0.05). Protein A-gold labeling of GLUT-2 in beta-cells of day 1 diabetic rats revealed 2.17 +/- 0.16 gold particles per micrometer length of microvillar plasma membranes compared to 3.91 +/- 0.14 in controls (P less than 0.001) and 2.87 +/- 0.24 in the nondiabetic diabetes-prone rats (P less than 0.02). Reduction in GLUT-2 correlates temporally with and may contribute to the loss of glucose-stimulated insulin secretion that precedes profound beta-cell depletion of autoimmune diabetes.

Animals↗