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PubMed1998

Effects of noradrenaline on the cell-surface glucose transporters in cultured brown adipocytes: novel mechanism for selective activation of GLUT1 glucose transporters.

Glucose transport into rat brown adipocytes has been shown to be stimulated directly by the sympathetic neurotransmitter, noradrenaline, without a significant increase in the protein content of either GLUT1 or GLUT4 glucose transporter in the plasma membrane [Shimizu, Kielar, Minokoshi and Shimazu (1996) Biochem. J. 314, 485-490]. In the present study, we labelled the exofacial glucose-binding sites of GLUT1 and GLUT4 with a membrane-impermeant photoaffinity reagent, 2-N-[4-(1-azitrifluoroethyl)benzoyl]-[2-3H]1,3-bis- (D-mannos-4-yloxy)-2-propylamine (ATB-[3H]BMPA), to determine which isoform is responsible for the noradrenaline-induced increase in glucose transport into intact brown adipocytes in culture. Insulin stimulated the rate of hexose transport by increasing ATB-[3H]BMPA-labelled cell-surface GLUT4. In contrast, the noradrenaline-induced increase in glucose transport was not accompanied by an increased ATB-[3H]BMPA labelling of GLUT4, nor with an increased amount of GLUT4 in the plasma membrane fraction as assessed by Western blotting, indicating that noradrenaline does not promote the translocation of GLUT4. However, noradrenaline induced an increase in photoaffinity labelling of cell-surface GLUT1 without an apparent increase in the immunoreactive GLUT1 protein in the plasma membrane. This is suggestive of an increased affinity of GLUT1 for the ligand. In fact, the Ki value of non-radioactive ATB-BMPA for 2-deoxy-D-glucose uptake was significantly decreased after treatment of the cells with noradrenaline. The increased photoaffinity labelling of GLUT1 and increased glucose transport caused by noradrenaline were inhibited by a cAMP antagonist, cAMP-S Rp-isomer. These results demonstrate that noradrenaline stimulates glucose transport in brown adipocytes by enhancing the functional activity of GLUT1 through a cAMP-dependent mechanism.

Adipose Tissue, Brown↗

PubMed1970

The operation of the gamma-aminobutyrate bypath of the tricarboxylic acid cycle in brain tissue in vitro.

1. Cerebral-cortex slices prelabelled with gamma-amino[1-(14)C]butyrate (GABA) were incubated in a glucose-saline medium. After the initial rapid uptake there was no appreciable re-entry of (14)C into the GABA pool, either from the medium or from labelled metabolites formed in the tissue. The kinetic constants of GABA metabolism were determined by computer simulation of the experimental results by using mathematical procedures. The GABA flux was estimated to be 0.03mumol per min/g, or about 8% of the total flux through the tricarboxylic acid cycle. It was found that the assumption of compartmentation did not greatly affect the estimates of the GABA flux. 2. The time-course of incorporation of (14)C into amino acids associated with the tricarboxylic acid cycle was followed with [1-(14)C]GABA and [U-(14)C]-glucose as labelled substrates. The results were consistent with the utilization of GABA via succinate. This was confirmed by determining the position of (14)C in the carbon skeletons of aspartate and glutamate formed after the oxidation of [1-(14)C]GABA. These results also indicated that under the experimental conditions the reversal of reactions catalysed by alpha-oxoglutarate dehydrogenase and glutamate decarboxylase respectively was negligible. The conversion of [(14)C]GABA into gamma-hydroxybutyrate was probably also of minor importance, but decarboxylation of oxaloacetate did occur at a relatively slow rate. 3. When [1-(14)C]GABA was the labelled substrate there was evidence of a metabolic compartmentation of glutamate since, even before the peak of the incorporation of (14)C into glutamate had been reached, the glutamine/glutamate specific-radioactivity ratio was greater than unity. When [U-(14)C]glucose was oxidized this ratio was less than unity. The heterogeneity of the glutamate pool was indicated also by the relatively high specific radioactivity of GABA, which was comparable with that of aspartate during the whole incubation time (40min). The rates of equilibration of labelled amino acids between slice and medium gave evidence that the permeability properties of the glutamate compartments labelled as a result of oxidation of [1-(14)C]GABA were different from those labelled by the metabolism of [(14)C]glucose. The results showed therefore that in brain tissue incubated under the conditions used, the organization underlying metabolic compartmentation was preserved. The observed concentration ratios of amino acids between tissue and medium were also similar to those obtaining in vivo. These ratios decreased in the order: GABA>acidic acids>neutral amino acids>glutamine. 4. The approximate pool sizes of the amino acids in the different metabolic compartments were calculated. The glutamate content of the pool responsible for most of the labelling of glutamine during oxidation of [1-(14)C]GABA was estimated to be not more than 30% of the total tissue glutamate. The GABA content of the ;transmitter pool' was estimated to be 25-30% of the total GABA in the tissue. The structural correlates of metabolic compartmentation were considered.

Alanine↗

PubMed1987

Features of amino acid metabolism in Moniliformis moniliformis (Acanthocephala) in vitro.

Experiments to investigate the metabolism of glycine, L-glutamic acid and L-aspartic acid by Moniliformis moniliformis were carried out by incubating adult worms aerobically for 3 h at 37 degrees C in Tyrode's solution containing either [U-14C]glycine, L-[U-14C]glutamic acid, L-[U-14C]aspartic acid or L-[4-14C]aspartic acid. Much of the glycine and glutamic acid was absorbed by the worms, but little of either was metabolized. Aspartic acid was readily taken up and metabolized. After incubating with L[U-14C]aspartic acid, most radioactivity was found in ethanol and a volatile compound, presumed to be carbon dioxide, with smaller amounts in lactate, alanine, acetate, malate, glucose and succinate. After incubating with L-[4-14C]aspartic acid, most radioactivity was found in lactate and the presumed CO2 with small amounts in alanine, malate and succinate. No radioactivity was found associated with ethanol or acetate. Possible metabolic pathways and suggestions for a relationship between the metabolism of aspartate with that of alanine and serine in this parasite are discussed.

Acanthocephala↗

PubMed1975

Analysis of growth rate in sucrose-supplemented cultures of Streptococcus mutans.

In the presence of sucrose, Streptococcus mutans grows in large glucan-containing aggregates. Because of reports of linear rather than exponential growth of sucrose-grown cultures, the kinetics of growth of sucrose-grown cultures of S. mutans strain OMZ-176 were compared with those of glucose-grown cultures. Culture turbidity measurements indicated that growth of sucrose cultures was slower, did not follow exponential kinetics, and slowed and stopped at lower absorbance values than did glucose-grown cultures. However, measurements of the rates of accumulation of deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and protein using fully equilibrated radioactively labeled precursors of each of these macromolecular species in sucrose and glucose-grown cultures showed that: (i) for glucose cultures the synthesis of each of the three informational molecules occurred at the same exponential rate, which was identical to the rate of turbidity increase; (ii) for sucrose cultures each macromolecular species was synthesized at the same exponential rate and these rates were identical to the rate of increase of turbidity of the glucose-grown culture for periods of up to 7 h. Furthermore, the ratios of DNA to RNA, RNA to protein, and protein to DNA for the sucrose cultures were identical to those for the glucose cultures for up to 10 doublings. From these data it was concluded that in the presence of sucrose S. mutans grows in a balanced fashion at the same exponential rate as it does in glucose. The deviation from an exponential growth model of the absorbance in sucrose cultures was attributed to an optical artifact due to the formation of large glucan-containing aggregates of cells. The addition of dextranase to sucrose cultures resulted in cultures which increased in turbidity at the same exponential rate as glucose-grown cultures, without affecting the rate or extent of macromolecular synthesis.

Carbon Radioisotopes↗

PubMed1989

Sucrose 6-alpha-D-glucosyltransferase from Streptococcus sobrinus: characterization of a glucosyl-enzyme complex.

A covalent glucosyl-enzyme was isolated from a quenched reaction of Streptococcus sobrinus sucrose 6-alpha-D-glucosyltransferase and radiolabeled sucrose. No complex was observed with heat-inactivated enzyme or when sucrose was replaced with radiolabeled maltose or glucose. The complex was stable at pH 2 in 1% sodium dodecyl sulfate, 6.0 M urea, and 4.0 M guanidine hydrochloride, but became increasingly labile with increased pH (32-min half-life at pH 7.0). D-Glucose was the exclusive radiolabeled compound identified when all radioactivity was released under mild alkaline conditions. Glucosyl-enzyme hydrolysis rates were linearly dependent on hydroxide ion concentration, giving a second-order rate constant of 2.15 x 10(5) M-1 min-1. When compared to the base lability of known glycosyl amino acid derivatives, the pH dependency of the glucosyl-enzyme most closely paralleled a glucosyl linkage to a carboxyl group. A novel application of a carbohydrate high-performance liquid chromatography column in aqueous solution was used to identify the anomeric form of D-glucose released on (i) alkaline hydrolysis of denatured glucosyl-enzyme and (ii) native enzyme hydrolysis of sucrose. The beta-anomer was identified in the former case and the alpha-anomer in the latter. The results with the denatured glucosyl-enzyme are consistent with a beta-glucosyl ester linkage to an aspartic or glutamic acid that hydrolyzes at the ester carbon with retention of anomeric configuration; for native glucosyltransferase catalysis, the data are consistent with a beta-glucosyl covalent intermediate as well, where deglucosylation occurs by attack at the acetal carbon with anomeric inversion.(ABSTRACT TRUNCATED AT 250 WORDS)

Carbon Radioisotopes↗

PubMed1983

Identification and characterization of the rat adipocyte glucose transporter by photoaffinity crosslinking.

The photoaffinity crosslinking agent hydroxysuccinimidyl-4-azidobenzoate has been used to attach [3H]cytochalasin B to a rat adipocyte low-density microsomal membrane protein of 45-50 kDa. The characteristics of the [3H]cytochalasin B-labeled protein are consistent with those of the adipocyte glucose transporter. The low-density microsomes from cells incubated without insulin incorporate twice the amount of radioactivity per mg membrane protein than low-density microsomes derived from insulin-stimulated cells. This value agrees with the distribution of glucose transporters measured in this intracellular membrane fraction prepared from basal and insulin-treated cells by [3H]cytochalasin B binding. Preincubation of membranes with 500 mM D-glucose reduces the photoaffinity crosslinking by 48% relative to that observed with 500 mM L-glucose. Isoelectric focusing of low-density microsomes containing the photoaffinity crosslinked transporter yields three bands of radioactivity focusing at pH values of 5.5, 4.5, and 4.2 respectively. Following isolation from the isoelectric focusing gel and SDS-polyacrylamide gel electrophoresis, all three peaks can be shown to contain a band of 45-50 kDa which crossreacts with an antiserum raised against the purified human erythrocyte glucose transporter. These results suggest that the identification, isolation and purification of the adipocyte glucose transporter is now possible using the techniques described above.

Adipose Tissue↗

PubMedDate not supplied

Radiorespirometric patterns of 14C-substrates in rats. I. Differences in kinds of 14C-substrates and their structural positions labelled with 14C.

Experiments were conducted by radiorespirometry to elucidate the relation between the respiratory 14CO2 wave pattern derived from intravenously injected 14C-substrates and the dispositional partition of these substrates in rats. Two types of 14C-methionine and 4 types of 14C-glucose molecules were used as the 14C-substrates. The respiratory 14CO2 wave patterns obtained in experiments using 14C-methionine substrates revealed different patterns based on differences in the labelled position and the amount of expired 14C-radioactivity as well as the wave height. The experiments using 14C-glucose substrates reveals that the carbon atoms participate equally in forming the respiratory 14CO2 wave pattern, regardless of their position in the glucose molecule. Moreover, differences in wave height as a result of differences in position of the labelled carbon atom were not observed. Results of 90-minute 14CO2 radioactivity recovery rate substantiated the explanation of the above-described relationship. The experiments also clarified that wave height is determined by rate of partition to the CO2 pathway of intermediate metabolites arising in the process of labelled 14C atom disposition.

Animals↗

PubMed2004

Stimulation by D-glucose of 36Cl- efflux from prelabeled rat pancreatic islets.

D-glucose was previously reported to cause a concentration-related decrease in the 36Cl- content of prelabeled islets prepared from ob/ob mice, a current animal model of inherited obesity. From these findings, it was inferred that the hexose stimulates Cl- efflux from islet cells and that such an increase in Cl- permeability may partly mediate glucose-induced depolarization of insulin-producing cells. The aim of the present study was to investigate the possible extension of these findings to islets prepared from normal rats by measuring the changes evoked by increasing concentrations of D-glucose in 36Cl- outflow itself from prelabeled isolated islets. After 60 min preincubation at 37 degrees C in the presence of 3 mM D-glucose and 36Cl- (75 microCi/mL), the islets were incubated for 8-10 min at 37 degrees C in the presence of increasing concentrations of the hexose (3-20 mM). The changes in 36Cl- outflow during incubation indicated that D-glucose, in excess of a threshold concentration close to 5 mM, indeed increases effluent radioactivity from the prelabeled islets. It is proposed, therefore, that a gating of volume-sensitive anion channels in glucose-stimulated insulin-producing islet cells participates in the depolarization of the plasma membrane recorded in the range of insulinotropic concentrations of the hexose.

Animals↗

PubMed1987

Effect of low temperatures on glucose-induced insulin secretion and ionic fluxes in rat pancreatic islets.

The direct effect of cold on the inhibition of B cell secretion is well known in hibernating and experimentally hypothermic mammals. This temperature dependency may result from the inhibition of ion transport across the membranes. In order to verify this hypothesis, ionic effluxes and insulin secretion from rat islets loaded with 86Rb+ and 45Ca+ were measured during perifusion. At 37 degrees C, the rise in glucose concentration from zero to 16.7 mmol/l provoked a rapid decrease in 86Rb+ efflux, an early fall and subsequent rise in 45Ca2+ efflux and a typical biphasic pattern of insulin secretion. At 27 degrees C, glucose induced only a very slight increase in insulin secretion, while the fluxes of radioactive ions were not significantly modified in amplitude but were clearly delayed. At 17 degrees C, no insulin response to glucose was observed and the decrease in K+ conductance indicated by 86Rb+ flux decrease was less temperature-dependent than the movement of Ca2+. After supplementary stimulation with a high extracellular concentration of Ca2+, insulin secretion was enhanced at 27 degrees C and reached levels induced by glucose alone at 37 degrees C. An increase in hormone secretion occurred even at 17 degrees C, but only during a first phase of secretion. Regular increases in temperature potentiated insulin secretion and provoked changes in ionic fluxes which suggest that B cell depolarization (86Rb+ flux decrease) induced by glucose can occur at 15 degrees C but cannot induce the opening of voltage-dependent Ca2+ channels (increase in 45Ca2+ efflux) until temperatures higher than 27 degrees C are reached.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1969

Lipoprotn lipase content and triglyceride fatty acid uptake in adipose tissue of rats of differing body weights.

Increasing body weight appears to alter lipid metabolism in adipose tissue. We have measured the content of lipoprotein lipase and the uptake of chylomicron triglyceride fatty acids in epididymal fat pads of rats of different weights. In order that the results might be expressed in terms of cell numbers, the relationship between the weights of fat pads and the numbers and volumes of fat cells isolated from them was determined. Highly significant correlations were found between fat pad weight and both the number and the volume of the individual adipocytes. In rats weighing from 140 to 350 g, the increase in the size of fat pads was attributable almost equally to increases in cell size and in cell number. Lipoprotein lipase activity was measured in acetone powders of whole fat pads and of isolated fat cell preparations. With both, lipoprotein lipase activity per cell diminished significantly as the weight of fat tissue increased, i.e., larger fat cells contained less enzyme per cell than smaller cells. The uptake of triglyceride fatty acid radioactivity was measured after incubation of fat pads with radiolabeled rat lymph chylomicrons in flasks containing either buffer alone or with added glucose or glucose plus insulin. The addition of glucose and insulin led to a mean increase of 70% in the uptake of radioactivity, but larger adipocytes were stimulated less than smaller cells. This resulted in a significant negative correlation between the weights of fat pads and the uptake of radioactivity. Enlargement of fat cells also led to a diminution in their capacity to esterify fatty acids.

Adipose Tissue↗

PubMed1985

Effects of L-dopa-induced dopamine accumulation on 45Ca2+ efflux and insulin secretion in isolated rat islets.

It has previously been demonstrated in several species that the secretory granules of pancreatic beta-cells have the ability to store substantial amounts of calcium and bioactive amines, such as dopamine and serotonin. Furthermore, evidence for a similar topographical localization for amine and calcium within the periphery of the granules has been obtained. In the present study, a possible interaction between dopamine and calcium on insulin release was investigated. Isolated rat islets were loaded with 45Ca2+ in the presence of theophylline and high glucose and then perifused in a dynamic system where radioactivity and insulin were determined in the effluent. When perifused in a bicarbonate buffer with 2 mmol/l Ca2+ and supplemented with the monoamine oxidase inhibitor pargyline, L-3,4-dihydroxyphenylalanine (L-dopa)-induced dopamine accumulation in the islets brought about a slight and transient increase in 45Ca2+ efflux. This increase was more pronounced and sustained in a Ca2+-deficient buffer or in a Ca2+-deficient buffer supplemented with ethyleneglycolbis(aminoethylether)tetraacetic acid (EGTA). Insulin release was transiently stimulated by islet dopamine accumulation in the Ca2+-deprived media, but not in a medium with 2 mmol/l Ca2+. Glucose-induced insulin release in 2 mmol/l Ca2+ was potentiated by acute dopamine accumulation. The combined effect of glucose stimulation and islet accumulation of dopamine induced a transient insulin release in the Ca2+-deprived media with and without EGTA. This release of insulin was accompanied by an increased 45Ca2+ efflux which was most pronounced in the presence of EGTA. Stimulation with glucose alone, i.e. without addition of L-dopa tended to decrease insulin release and 45Ca2+ efflux in a Ca2+-deficient medium. No effects of L-dopa or L-dopa + glucose were encountered in a Ca2+-deficient buffer when the monoamine oxidase inhibitor pargyline was replaced by the dopa-decarboxylase inhibitor benserazide. The results are interpreted as being a consequence of a complex interaction between the accumulated dopamine and a pool of Ca2+ mainly confined to the secretory granules. This interaction could be followed by a transient increase in cytosolic Ca2+ and a subsequent efflux of Ca2+ out of the cell, eventually accompanied by insulin release. Increasing the cytosolic Ca2+ by acute dopamine accumulation makes the cell more sensitive to a concomitant stimulation with glucose, and the release of insulin is triggered. A long-term dopamine accumulation. On the other hand, might diminish the granular Ca2+ pool to such a level where insulin release is inhibited after stimulation with certain secretagogues.

Animals↗

PubMed1968

The presence of glycopeptide material in cultured mouse mast-cell tumours.

1. Mouse mast-cell tumours P815 Y and HC were shown to contain glycoprotein material composed of glucosamine, galactosamine, sialic acid, galactose and mannose. 2. The major amino acids released after acid hydrolysis of Pronase-treated digests of the glycoprotein are aspartic acid, glutamic acid, serine, threonine, proline, glycine and alanine. The Pronase-digested material is not degraded in alkaline solution. 3. On incubation of mast cells with [(35)S]sulphate, heparin is the major radioactive product. However, [1-(14)C]glucosamine and d-[(14)C]glucose are incorporated largely into the glycoprotein. 4. The fate of [(35)S]sulphate-labelled and [1-(14)C]glucosamine-labelled material was studied. In each case high-molecular-weight radioactive material is released from the cells into the culture medium. The t((1/2)) of [(35)S]sulphate-labelled material in cells is 70hr. and that of [1-(14)C]-glucosamine-labelled material in cells is 40hr. 5. About 60% of the [(35)S]sulphate-labelled material is present in the mitochondrial and granular fraction. [1-(14)C]-Glucosamine-labelled material is present in both microsomal and mitochondrial and granular fractions, [(14)C]sialic acid being concentrated in the microsomal fraction.

Amino Acids↗

PubMed2000

The cercarial tail in Proterometra macrostoma (Digenea: Azygiidae): permeability and fine structure of the tegument.

Permeability of the cercarial tail in Proterometra macrostoma was examined in vitro with 1 mM 3H-glucose, which tails absorb by diffusion alone. Naturally emerged cercariae (bodies withdrawn into tails) were permeable, but they rapidly (3 min) equilibrated with glucose in the bathing medium and maintained steady state for 4 hr. Metabolism of absorbed glucose was not detectable until after 90 min, and radioactivity in bodies dissected from tails after 4 hr was negligible. On the basis of cercarial water content (90% of total weight) and absorbed isotope at steady state, the calculated volume of the equilibrating compartment was 4% of an intact cercaria. This value correlated well with that of the tegument (3-5%), which was 1-2 microm thick as seen by transmission electron microscopy. A continuous, electron-dense basal membrane/lamina separated the tegument from subtegument. We conclude that the glycocalyx and external plasma membrane are freely permeable, whereas the basal membrane is the barrier that effectively isolated the subtegument from exogenous glucose. The basal membrane also may be the primary structure that protects the subtegument and cercarial body from effects of osmotic stress.

Animals↗

PubMed1988

Glucose metabolism in Xanthomonas campestris and influence of methionine on the carbon flow.

The glucose flow in Xanthomonas campestris was investigated with radio-labelled glucose and by enzymological studies. Only 7% of the radioactivity was incorporated into the cell material, but 41% was oxidized to carbon dioxide and 28% transformed to xanthan. Up to 16% of cell dry weight consisted of the polysaccharide glycogen. In the presence of 2.7 mM methionine, which is an inhibitor of xanthan formation, increased carbon dioxide formation (51%) occurred. This increase was in accordance with a twofold increase in the NAD-dependent isocitrate dehydrogenase activity. The other carbon dioxide liberating enzyme, 6-P-gluconate dehydrogenase, was not influenced by methionine, but its occurrence indicates the presence of an active pentose phosphate pathway in X. campestris. Among the other enzymes detected in X. campestris was glucose dehydrogenase. The presence of this enzyme together with hexokinase indicates the operation of two different glucose metabolizing steps: one oxidative, the other phosphorylative. Only the latter directly provides phosphorylated glucose as a precursor for the activated sugars required for xanthan synthesis.

Carbon↗

PubMed1990

Improvement with metformin in insulin internalization and processing in monocytes from NIDDM patients.

This study investigated the relative effect of obesity alone and in combination with non-insulin-dependent diabetes mellitus (NIDDM) on the intracellular processing of insulin and evaluated the effect of metformin therapy on this process. Monocytes from 11 obese hyperinsulinemic subjects, 13 obese hyperinsulinemic NIDDM patients, and 7 nondiabetic control subjects were incubated with A14-125I-labeled insulin for 60 min at 37 degrees C, and intracellular insulin degradation was characterized by high-performance liquid chromatography. Total cell-associated insulin (insulin binding) and internalized and degraded insulin were decreased in obese subjects and significantly decreased in obese NIDDM patients compared with nondiabetic control subjects. In NIDDM patients, intracellular insulin degradation was inversely correlated with fasting plasma glucose (P less than 0.01). Eight obese subjects and 9 obese NIDDM patients were restudied after 4 wk of therapy with metformin (850 mg twice a day). Plasma levels of the drug were superimposable in the two groups. Metformin therapy did not change glucose and insulin levels in obese subjects but caused a decrease in blood glucose in obese NIDDM patients. Total cell-associated radioactivity (insulin binding) significantly increased in both groups (P less than 0.01). On the contrary, internalized radioactivity increased (0.83 +/- 0.3 vs. 1.31 +/- 0.35%, P less than 0.01), and similarly, insulin degradation was enhanced (54.6 +/- 8.9 vs. 74.22 +/- 9.15%, P less than 0.01) only in monocytes from obese NIDDM patients. However, the levels of these parameters were still lower than in control subjects (internalization, 2.94 +/- 0.68%; degradation, 93.03 +/- 3.7%).(ABSTRACT TRUNCATED AT 250 WORDS)

Biological Transport↗

PubMed1980

The priming effect of glucose in soil sterilized by gamma-radiation and reinoculated with Cellulomonas sp.

Mineralization of native organic matter and U-14C-glucose was followed by measuring the formation of CO2 and its radioactivity in chernozem soil presterilized by gamma-radiation and inoculated with a washed suspension of Cellulomonas sp. cells. The introduced bacteria mineralized the soil organic component to a higher extent in variants enriched with glucose. This so-called priming effect of glucose was observed also in the presence of chloramphenicol, inhibiting the growth of the bacteria. The increased mineralization of the native soil organic fraction was also detected in samples that were not enriched with glucose when the bacterial suspension was first disintegrated ultrasonically and the material then used for the inoculation. Possible participation of phenomena of the type of cometabolism and activation of cell membrane transport mechanisms on the occurrence of the priming effect of glucose in the soil is discussed.

Actinomycetales↗

PubMed1991

Inositol cycling and phosphoinositide metabolism in rat pancreatic islets.

The effects of extracellular inositol and LiCl on intra-islet inositol cycling were investigated in isolated rat islets. Islets were cultured for 7 days in inositol-free RPMI 1640 containing 11.1 mM glucose and labeled with 3.7 MBq myo-[2-3H] inositol for the final 3 days. The labeled islets were then perifused under various conditions. There was a persistent increase in [3H] efflux from labeled islets stimulated with 16.7 mM glucose for 60 min. Addition of 5 mM inositol resulted in marked release of [3H] from islets and a decrease in radioactive inositol-lipid. When islets were perifused with 5 mM LiCl, the glucose-induced efflux of [3H] was greatly inhibited. The inhibitory effect of LiCl on [3H] efflux was partially corrected by the addition of 5 mM inositol. A prominent effect of LiCl was an increase in inositol monophosphate, indicating increased phospholipase C activity. This was detected within 5 min after glucose stimulation. The present data suggest that there is always very active intra-islet inositol cycling and that glucose can augument inositol-lipid metabolism.

Animals↗

PubMed1984

Stimulation of retinal capillary pericyte protein and collagen synthesis in culture by high-glucose concentration.

The influence of glucose concentration on cell multiplication and protein synthesis was studied in synchronized, long-term cultures of bovine retinal microvessel pericytes. The cell multiplication rate and the mitotic rate were reduced in media containing 20 mM glucose to 57% and 54%, respectively, of that obtained in media containing 5 mM glucose. Elevated glucose, however, did not change the DNA content of individual cells. Protein and collagen synthesis were measured by the incorporation of radioactive proline and lysine, or the posttranslational production of hydroxyproline and hydroxylysine, respectively. High glucose stimulated protein and collagen synthesis per cell 2.2 +/- 0.10 (SD) and 2.1 +/- 0.06 times, respectively. Aspirin (0.5 mM), an inhibitor of nonenzymatic glycosylation, did not alter the effect of elevated glucose concentration on protein and collagen synthesis.

Animals↗