Exogenous Glucose Concentration Research Articles

Boosting starch productivity of mixotrophic duckweed via light and organic carbon treatment

Duckweeds is the most promising nonfood feedstock for sustainable bioenergy production. Mixotrophy is the best growth mode compared to photoautotrophy and heterotrophy for biomass and starch accumulation in duckweed. This work investigated the impacts of light intensities (3,000, 6,000, 9,000, 12,000, 15,000, and 20,000 lux) and exogenous glucose concentrations (5, 10, 15, 20, 30, and 40 g L−1) on the biomass and starch accumulation of mixotrophic duckweed. The results showed that increasing light intensity and the initially applied concentration of glucose enhanced both growth and starch content. However, high concentrations of glucose (15–40 g L−1) resulted in a higher biomass yield but concurrently greatly inhibited photosynthesis. Moreover, excess carbon was redirected into starch biosynthesis under high glucose. The maximum starch yield of 655.4 g m−2 was obtained at 40 g L−1 glucose, with a maximum starch content of 72.7% of dry biomass and a biomass yield of 1024.6 g m−2. The optimum light intensity for starch accumulation was 20,000 lux, with a maximum starch yield of 236.2 g m−2. These results indicated that high organic carbon levels are a robust way to promote starch production in mixotrophic duckweed.

Effect of Exogenous Glucose at Different Concentrations on the Formation of Dark-Brown Humic-like Substances in the Maillard Reaction Pathway Based on the Abiotic Condensation of Precursors Involving δ-MnO2

The Maillard reaction is a type of nonenzymatic browning process and is an important pathway for the formation of humic-like substances (HLSs). Glucose is one of the three crucial precursors for the Maillard reaction, and a change in glucose concentration can inevitably affect the humification pathway, thereby regulating the composition and quality of HLSs. To verify the scientific hypothesis, the method of liquid shake-flask culture was adopted. Both catechol and glycine with fixed concentrations were added to a phosphate buffer including δ-MnO2, and only the concentration of glucose was adjusted in the sterile culture system. The obtained supernatant fluid and dark-brown residue were collected dynamically through the centrifugation method. The E4/E6 ratio and total organic C (TOC) of the supernatant fluid, the humus composition, and FTIR spectra for the dark-brown residue, and the elemental composition of humic-like acid (HLA) extracted from the dark-brown residue were analyzed to reveal the effect of varying glucose concentrations on the abiotic humification pathways for the Maillard reaction and the characteristics of relevant products under abiotic processes. The results reveal that (1) the exogenous addition of glucose at different concentrations simplifies the molecular structure in the supernatant fluid, and the TOC content is decreased to varying degrees, among which the addition of 0.24 mol/L glucose leads to the formation of simpler organic molecules in the supernatant compared to that for the other treatments, and the addition of 0.03 mol/L glucose shows the largest decrease in TOC content; (2) Under the coexistence of glycine and catechol, CHLA treated with the addition of glucose at different concentrations shows an upward trend in the course of the culture, which is significantly higher than that obtained for the CK control. The addition of 0.12 mol/L glucose results in the largest increase in CHLA. During the culture period, the structure of HLA molecules from each treatment first become complex and then gradually become simpler. Finally, the molecular structure of HLA treated with different concentrations of glucose becomes more complex, but the structure of HLA molecules from the CK control tends to be simplified. The addition of glucose can improve the condensation degree of HLA molecules, among which the addition of 0.12 mol/L glucose shows the most significant effect. With increasing exogenous glucose concentration, the number of N-containing compounds in the HLA molecules further decreases, while the number of O-containing functional groups increases. (3) The greater the concentration of glucose added, the higher the proportion of aromatic C structures in the dark-brown residue. During this process, the Mn-O bond lattice vibration of the δ-MnO2 layered structure is greatly enhanced. The organic molecules in the dark-brown residue and δ-MnO2 are bound to each other through intermolecular hydrogen bonding. The CHLA/CFLA ratio for each treatment increases to varying degrees after the culture period, indicating that the addition of glucose is more conducive to the improvement of humus quality than the CK control, among which the addition of 0.12 mol/L glucose shows the best effect.

Simultaneous quantification of endogenous and exogenous plasma glucose by isotope dilution LC-MS/MS with indirect MRM of the derivative tag.

Quantification of endogenous and exogenous plasma glucose can help more comprehensively evaluate the glucose metabolic status. A ratio-based approach using isotope dilution liquid chromatography tandem mass spectrometry (ID LC-MS/MS) with indirect multiple reaction monitoring (MRM) of the derivative tag was developed to simultaneously quantify endo-/exogenous plasma glucose. Using diluted D-[13C6] glucose as tracer of exogenous glucose, 12C6/13C6 glucoses were first derivatized and then data were acquired in MRM mode. The metabolism of exogenous glucose can be tracked and the concentration ratio of endo/exo-genous glucose can be measured by calculating the endo-/exo-genous glucose concentrations from peak area ratio of specific daughter ions. Joint application of selective derivatization and MRM analysis not only improves the sensitivity but also minimizes the interference from the background of plasma, which warrants the accuracy and reproducibility. Good agreement between the theoretical and calculated concentration ratios was obtained with a linear correlation coefficient (R) of 0.9969 in the range of D-glucose from 0.5 to 20.0mM, which covers the healthy and diabetic physiological scenarios. Satisfactory reproducibility was obtained by evaluation of the intra- and inter-day precisions with relative standard deviations (RSDs) less than 5.16%, and relative recoveries of 85.96 to 95.92% were obtained at low, medium, and high concentration, respectively. The method was successfully applied to simultaneous determination of the endo-/exogenous glucose concentration in plasma of non-diabetic and type II diabetic cynomolgus monkeys. Graphical Abstract The scheme of the proposed ratio-based approach using isotope dilution LC-MS/MS with indirect MRM of the derivative tag for simultaneous quantification of endogenous and exogenous plasma glucose.

Promotion of glucose utilization by insulin enhances granulosa cell proliferation and developmental competence of porcine oocyte grown in vitro.

In vitro culture of the oocyte granulosa cell complexes (OGCs) from early antral follicles (EAFs) shows granulosa cell (GC) proliferation, but to a lesser extent than that observed in vivo during follicle development. As the number of GCs closely relates to energy sufficiency of the oocytes, enhancement of GC proliferation influences oocyte development. GC proliferation depends on glycolysis and insulin-mediated AKT/mTOR signaling pathway; therefore, addition of culture medium containing insulin and glucose may potentially promote GC proliferation and hence improve oocyte development. In the present study, we assessed the effect of exogenous insulin and glucose concentration on GC proliferation and oocyte energy status as well as developmental abilities of porcine oocytes grown in vitro. In the presence of 5.5 mM of glucose (Low), a comparison of 10 versus 20 μg/ml insulin showed that high insulin enhanced GC proliferation but exhausted glucose from the medium, which resulted in low energy status including lipid and adenosine triphosphate of the oocyte. Whereas, in the presence of 20 μg/ml insulin, medium with 11 mM glucose (High) enhanced GC proliferation and oocyte energy status as well as developmental ability up to the blastocyst stage. Considering that there was no difference in OGCs development observed with medium (10 μg/ml insulin) containing 5.5 versus 11 mM glucose, we concluded that the combination of high insulin and glucose enhanced GC proliferation and energy status of oocytes as well as the developmental ability of the oocytes grown in vitro.

Hepatic insulin sensitivity in healthy and prediabetic subjects: from a dual- to a single-tracer oral minimal model.

Recently, a model was proposed to assess hepatic insulin sensitivity during a meal, i.e., the ability of insulin to suppress glucose production (EGP), SI (P). The model was developed on EGP data obtained from a triple-tracer meal and the tracer-to-tracee clamp technique and validated against the euglycemic hyperinsulinemic clamp. The aim of this study was to assess whether SI (P) can be obtained from plasma concentrations measured after a single-tracer meal by incorporating the above EGP model into the oral glucose minimal model by describing both glucose production and disposal (OMM(PD)). Triple-tracer meal data of two databases (20 healthy and 60 healthy and prediabetic subjects) were used. Virtually model-independent EGP estimates were calculated. OMM(PD) was identified on exogenous and endogenous glucose concentrations, providing indices of SI (P), disposal insulin sensitivity (SI (D)), and EGP. The model fitted the data well, and SI (P) and SI (D) were estimated with precision in both databases (SI (P) = 5.48 ± 0.54 10(-4) dl·kg(-1)·min(-1) per μU/ml and SI (D) = 9.93 ± 2.18 10(-4) dl·kg(-1)·min(-1) per μU/ml in healthy; SI (P) = 5.41 ± 3.55 10(-4) dl·kg(-1)·min(-1) per μU/ml and SI (D) = 5.34 ± 6.17 10(-4) dl·kg(-1)·min(-1) per μU/ml, in healthy and prediabetic subjects). Estimated SI (P) and that derived from the triple-tracer EGP model were very similar on average. Moreover, the time course of EGP normalized to basal EGP (EGPb), and EGP/EGPb agreed with the results obtained using the triple-tracer method. In this study, we have demonstrated that SI (P), SI (D), and EGP/EGPb time course can be estimated reliably from a single-tracer meal protocol in both healthy and prediabetic subjects.

Hepatic Insulin Sensitivity Assessed by Integrated Model of Hepatic and Peripheral Glucose Regulation

The integrated model of hepatic and peripheral glucose metabolism incorporates a model for liver glucose metabolism into the two-compartment minimal model framework to describe endogenous glucose kinetics during a labeled intravenous glucose tolerance test (IVGTT). This model also provides a parametric description of endogenous glucose production (EGP). The present study extended the theoretical potential of the model by defining hepatic glucose effectiveness (hS(G)(2)) as the ability of glucose per se to inhibit EGP and hepatic insulin sensitivity (hS(1)(2)) as the ability of insulin to enhance glucose suppression of EGP. As a retrospective data base review of our previous study, we re-analyzed time courses of exogenous and endogenous glucose concentration during [6,6-(2)H(2)]glucose-labeled IVGTT (0.3 g/kg glucose), performed in 11 exercise-trained and 12 age-matched sedentary subjects. Model parameters of the two-compartment minimal model and of liver glucose metabolism were simultaneously identified to assess insulin sensitivity specific to stimulate glucose uptake (S(1)(2*)) and that specific to inhibit EGP (hS(1)(2)). The abilities of glucose per se to stimulate its own uptake (S(G)(2*)) and to inhibit EGP (hS(G)(2)) were also estimated. Parameters of the integrated model were identified in all the subjects. Hepatic insulin sensitivity consisted of about one-third of total insulin sensitivity (S(1)(2*) + hS(1)(2)). Compared with the sedentary subjects, S(1)(2*), hS(1)(2), hS(G)(2) of the trained subjects were greater. Because insulin resistance in liver and peripheral tissue may play a differential role in the pathogenesis of diabetes, this analysis can serve as a simple one-step approach to obtain metabolic indexes specific to EGP suppression and stimulating glucose uptake.

C-myc Promoter Binding Protein Regulates the Cellular Response to an Altered Glucose Concentration

Alpha-enolase is a bifunctional gene encoding both a glycolytic enzyme and a DNA binding protein, c-myc binding protein (MBP-1). MBP-1 binds the c-myc promoter and downregulates c-myc transcription. Since these alpha-enolase gene products have important functions in glucose metabolism and growth regulation, this gene may play a central role in regulating the abnormal proliferative characteristics of transformed cells. To determine the role of alpha-enolase and MBP-1 in the cellular response to altered exogenous glucose concentration, MCF-7 cells were cultured in low (1 nM), physiological (5 mM), or high (25 mM) levels of glucose. Levels of alpha-enolase, MBP-1, and c-myc expression were compared to levels of cell proliferation and lactate production. At all glucose concentrations, MCF-7 cells demonstrated an initial increase in MBP-1 expression and a parallel decrease in c-myc transcript levels, which were accompanied by decreased proliferation. Cells grown in low glucose maintained the increased MBP-1 expression through 48 h, resulting in persistently lower rates of proliferation. However, physiologic or high glucose levels resulted in decreased MBP-1 expression, which was associated with increased cellular proliferation and lactate production. In these cells, c-myc mRNA returned to control levels as MBP-1 expression decreased. Cells grown in low glucose demonstrated a dramatic increase in c-myc mRNA at 48 h, which was associated with a loss in c-myc P2 promoter binding by MBP-1. This suggests that post-translational modifications of MBP-1 likely alter its DNA binding activity. These results demonstrate an important role for MBP-1 in the altered cell proliferation and energy utilization that occur in response to an altered glucose concentration.

Manipulation of ethanol production in anoxic rice coleoptiles by exogenous glucose determines rates of ion fluxes and provides estimates of energy requirements for cell maintenance during anoxia

Ethanol production by anoxic, excised, 7-10 mm tips of rice coleoptiles was manipulated using a range of exogenous glucose concentrations. Such a dose-response curve enabled good estimates at which level of ethanol production (and hence by inference ATP production), injury commenced and also allowed assessments of energy requirements for maintenance in anoxia. Rates of net uptake or loss of K+ and P by these excised coleoptile tips were related to rates of ethanol production (r2 of 0.59 and 0.68, respectively). At 72 h anoxia, ATP levels in excised tips were similar at 0, 2.5, and 50 mol m(-3) exogenous glucose, despite large differences in the inferred rates of ATP production. At 96 h anoxia, tips without exogenous glucose had low ATP concentrations; these may be the cause or the consequence of cell injury. In tips without glucose, injury was indicated by losses of K+ and Cl- between 72-96 h anoxia, and during the first hour after re-aeration, while later than 1 h after re-aeration, rates of net uptake were substantially lower than for re-aerated tips previously in anoxia with exogenous glucose. Between 96 h and 124 h anoxia, ion losses from tips without exogenous glucose increased while recovery of net uptake after re-aeration was very sluggish and incomplete. The energy requirement for maintenance of health and survival of anoxic coleoptile tips, expressed on a fresh weight basis, was lower than for three other anoxia-tolerant plant tissues/cells, studied previously. However, the energy requirement on a protein basis was assessed at 1.4 micromol ATP mg(-1) protein h(-1) and this value is 2.6-5.4-fold higher than for the other plant tissues/cells. Yet, this requirement was still only 58-88% of the published values for aerated tissues. The reason for this relatively high ATP requirement per unit protein in anoxic rice coleoptiles remains to be elucidated.

Hyperglycemia-induced changes in hepatic membrane fatty acid composition correlate with increased caspase-3 activities and reduced chick embryo viability

Fertile chicken eggs were injected with various concentrations of either d-glucose or l-glucose during the first three days of embryonic development. The exogenous glucose concentrations ranged from 0 to 18.58 μmol/kg egg. At 18 days of development (theoretical stage 44), brains, livers, and blood from chorio-allantoic vessels were isolated from living embryos. Exogenous d-glucose and l-glucose caused increased plasma d-glucose levels, increased plasma alanine aminotransferase (ALT) activities, and decreased embryo viability. Embryo viability was monitored by a reduction in the percentage of living embryos at theoretical stage 44, reduced embryo masses, reduced brain masses, and reduced liver masses. When compared to controls, embryonic exposure to either exogenous d-glucose or l-glucose caused increased caspase-3 activities and increased lipid hydroperoxide (LPO) levels in both brain and liver tissues. Because lipid hydroperoxides are lipid peroxidation intermediates that result in the attack of any unsaturated neutral lipid or unsaturated phospholipid, the effect of exogenous glucose on hepatic membrane fatty acid composition was studied. Exogenous glucose (either d-glucose or l-glucose) promoted reduced levels of several unsaturated, long-chain fatty acids and increased levels of saturated, short-chain fatty acids within hepatic membranes. Exogenous-glucose induced decreases in the ratios of unsaturated/saturated fatty acids and long-chain/short-chain fatty acids within hepatic membranes which strongly correlated with glucose-induced increases in plasma ALT activities and moderately correlated to hepatic LPO levels. These observations are consistent with the hypothesis that embryonic hyperglycemia promotes hepatic membrane lipid peroxidation and hepatic cell death.

Energy metabolism in pig oocytes and early embryos.

Pig oocytes and embryos differ from those of other species in having a large quantity of endogenous lipid, a potential role for which has yet to be identified. In the present study, the hypothesis that endogenous triglyceride acts as a metabolic substrate during in vitro maturation and early embryo development was tested. Embryos were produced by in vitro fertilization (IVF) of in vitro-matured, abattoir-derived immature oocytes, cultured in medium NCSU23 up to the blastocyst stage. The triglyceride content of single oocytes and embryos was measured throughout development. Oxygen and glucose consumption and the formation of lactate were measured non-invasively over the same period, enabling total ATP production to be calculated. The triglyceride content of oocytes before maturation (135+/-4.9 ng) decreased by 13 ng (P<0.05) during in vitro maturation, but there was no apparent change in triglyceride content during embryo development (117.68 ng). Oxygen consumption was low throughout embryo cleavage before reaching a peak at the blastocyst stage (P<0.01), a pattern similar to that seen in other mammals studied. Glucose consumption and lactate production were also at a maximum at the blastocyst stage (P<0.05). These data indicate that pig oocytes may use endogenous triglyceride as an energy source during in vitro maturation and that most (91-97%) of the ATP produced during embryo development comes from oxidative phosphorylation. The high exogenous glucose concentration in NCSU23 (5.5 mmol l(-1)) may be needed to form pyruvate, which in turn, produces oxaloacetate, which is required to prime the tricarboxylic acid cycle. However, the reason for the high lipid content in early pig embryos remains to be elucidated.

Fructose-2,6-bisphosphate, a potent stimulator of phosphofructokinase, is increased by high exogenous glucose perfusion.

We have previously demonstrated that perfusion of isolated hearts with high concentrations of glucose results in increased glycolysis during ischemia, diminished ischemic injury, and improved functional recovery with reperfusion. To evaluate a possible mechanism by which glucose conferred this protection. We examined the hypothesis that increased exogenous glucose concentrations results in increased concentrations of fructose-2,6-bisphosphate, a potent activator of phosphofructokinase-1, and thus increases glycolysis. Perfused rabbit hearts were subjected to 60 min of low-flow ischemia. Control hearts were perfused with buffer containing 0.4 mmol/l palmitate, 5 mmol/l glucose, and 70 mU/l insulin, and treated hearts were perfused with buffer containing 0.4 mmol/l palmitate, 15 mmol/l glucose and 210 mU/l insulin. Ischemic contracture was attenuated by perfusion of high concentrations of glucose (high glucose) (P < 0.05 compared with control). Glucose uptake and lactate production were greater in hearts perfused with high glucose, as was the ATP concentration at the end of ischemia (P < 0.05 compared with controls). Exogenous glucose uptake and lactate production correlated well with fructose-2,6-bisphosphate content (P = 0.007). Enhancement of glycolysis in hearts perfused with high glucose may be the result of stimulation of phosphofructokinase-1 by fructose-2,6-bisphosphate. Accordingly, this may serve as an important mechanism by which cardioprotection may be achieved.

Histological Characterization and Glucose Incorporation into Glycogen of the Pacific Oyster Crassostrea gigas Storage Cells.

In order to investigate glycogen metabolism in the oyster Crassostrea gigas, the distribution of storage cells in the whole animal was studied before histological and biochemical characterization. These cells were found mainly in the labial palps, the mantle, and gonadal area and also in gills and the digestive area. Storage cells from palps, mantle, and gonad presented the same morphological features and the same seasonal glycogen variations. Storage cells were isolated from the labial palps and the mantle plus gonadal area of the oyster by enzymatic dispersion and centrifugation through discontinuous Percoll gradient. These cells have a modal density of 1.043 g/ml. An ultrastructural study confirmed that glycogen is present in the cytoplasm either as fine particles or sequestered within vesicles. Glucose incorporation into glycogen was evaluated in vitro using [U-(14)C]glucose: the incorporation in isolated cells increased linearly for at least 8 hours, was proportional to the cell concentration, and showed saturation kinetics with respect to the exogenous glucose concentration.

Effects of exogenous glucose on mycorrhizal colonization in vitro by early-stage and late-stage ectomycorrhizal fungi

Under aseptic conditions, seedlings of 12 common tree species found in eastern Canada (Alnus rugosa, Betula papyrifera, Betula alleghaniensis, Abies balsamea, Tsuga Canadensis, Pinus strobes, Pinus resinosa, Pinus banksiana, Larix laricina, Picea glauca, Picea mariana, and Picea rubens) were inoculated with 10 species of ectomycorrhizal fungi (Piloderma bicolour, Lactarius thyinos, Lactarius subpurpureus, Lactarius torminosus, Hebeloma longicaudum, Cenococcum geophilum, Suillus sinuspaulianus, Suillus tomentosus, Leccinum holopus, and Boletinus paluster) in the absence or presence of exogenous glucose (2 g/L). Early-stage ectomycorrhizal colonizers with a broad host range (e.g., H. longicaudum) appeared to be less dependent upon the exogenous carbohydrate supply for successful formation of ectomycorrhizae than were host-specific late-stage ectomycorrhizal colonizers (e.g., Lactarius subpurpureus). Further investigations revealed, however, that while levels of exogenous glucose (1.0 and 10.0 g/L) increased mycelial growth of late-stage ectomycorrhizal colonizers, a detrimental effect on the growth of the seedlings took place in the presence of these fungi, rather than a concurrent increase in colonization and infection of the host roots. It is suggested that secondary fungal metabolites toxic to the plants are released as a consequence of increased mycelial growth in response to an increase in glucose concentrations. Thus, when dealing with late-stage ectomycorrhizal colonizers and host plants in mycorrhizal synthesis experiments, the exogenous glucose concentration is critical. Key words: early-stage fungi, late-stage fungi, ectomycorrhizae, glucose, root colonization, fungal metabolites.

Glucose utilization rates are linked to the internal free glucose gradient in the rat tapeworm

Hymenolepis diminuta is able to acquire plasma-borne glucose 3- O-[ 14C]methyiglucose) in vivo. Free glucose concentrations estimated for this helminth in vivo are comparable to that of the host intestine. Both in vivo and in vitro examinations indicate that the scolex-neck regions (first quartile) of this tapeworm have the highest glucose content, and an anterior-posterior gradient along the second, third, and fourth quartiles was observed. Substrate concentration was rate affecting for glucose utilization rates (measured as substrate depletion from the medium in vitro). Glucose utilization per minute exceeds glucose content by a factor of more than 5. The half-life of glucose was about 10 sec, emphasizing that sugar metabolism is a very rapid process. In addition, utilization was highest in the first quartile and decreased in succession in the second, third, and fourth quartiles. It is concluded that while the exogenous glucose concentration remains stable, regional differences in glucose utilization rates are linked ( R = 0.98; P < 0.01) to free glucose content in H. diminuta.

Compartmentalization of radioactive glucose in the plerocercus metacestode of Otobothrium insigne (Cestoda: Trypanorhyncha)

Otobothrium insigne plerocerci were used to study the compartmentalization of radioactive glucose in a metacestode bladderworm under in vitro conditions. When plerocerci were incubated in C 14-labeled glucose, this glucose was rapidly absorbed by the blastocyst outer-wall tegument. Within minutes, this absorbed glucose diffused through the blastocyst wall and into the blastocyst cavity. Over 95% of the absorbed glucose remained as free glucose in the blastocyst walls and cavity even after 2 h post-incubation. When plerocerci were first pulse-incubated in radioactive glucose for 30 min, and then chase-incubated in glucose-free saline for several days, the quantity of unbound radioactive glucose in the blastocyst walls and cavity decreased significantly during the first 48 h while the quantity in the scolex increased. The radioactivity of the blastocyst wall glycogen and scolex glycogen both increased during this time; however, the scolex incorporated significantly more radioactive glucose into its glycogen than did the blastocyst wall in spite of the wall's larger quantity of endogenous glycogen and its closer proximity to the large glucose pool of the blastocyst cavity. Thus, it appears that under conditions where exogenous glucose concentrations are low, the juvenile scolex takes nutritional precedence over the blastocyst such that glucose is diverted from the blastocyst walls to the scolex in order to maintain carbohydrate steady state conditions in the scolex.

Sugar Transport and Sulfite Action in Etioprotoplasts, Semi‐Etioprotoplasts and Green Protoplasts of Avena sativa L.

AbstractThe mechanism of glucose and sucrose transport and the influence of various concentrations of sulfite on its activity was studied in mesophyll protoplasts (etioprotoplasts, semi‐etioprotoplasts and green protoplasts) isolated from oat (Avena sativa L.) seedlings.Kinetic analysis of [14C] glucose loading (in darkness) revealed in each kind of protoplasts the presence of two transport components. At low exogenous glucose concentrations a saturable system was the main mode of transport. At concentrations higher than 20 mM the loading of glucose in all types of protoplasts was dominated by a non‐saturable, linear diffusion‐like component. The rate of glucose uptake was greatest in etioprotoplasts and lowest in green protoplasts.In contrast to the above we have not found saturable components of sucrose transport in any kind of protoplasts. The rate of its uptake was greatest in semi‐etioprotoplasts.Sulfite, at a concentration of &lt; 1.0 mM stimulated and at ≥ 1.0 mM inhibited the uptake of glucose to etioprotoplasts and semi‐etioprotoplasts and inhibited that to green protoplasts at any concentration. The transport of sucrose underwent a significant inhibition in the various types of protoplasts only under the influence of 10.0 mM of sulfite ions.Inhibition of glucose uptake by sulfite was of the non‐competitive type.Sulfite also affected the level of adenylic nucleotides and lowered the energy charge and ATP/ADP ratio.Intensity of sulfite uptake was significantly higher in green protoplasts than in etioprotoplasts.

Isolation, characterization and glucose metabolism of glycogen cells (=vesicular connective-tissue cells) from the labial palps of the marine mussel Mytilus edulis

A method has been developed to isolate glycogen cells (=vesicular connective tissue cells) from the labial palps of the marine mussel Mytilus edulis L. These cells have a modal density of 1.14 g ml-1 and this property has been exploited to separate them from pronase-dissociated cell dispersions by density-gradient centrifugation. The isolated cells were mainly spherical, with a small peripheral nucleus. The quasitotality of the cell was filled with β-like glycogen particles with cellular organelles being limited to the cell periphery. The major recipients of [U-14C] glucose-derived carbon were glycogen and amino acids. Only small quantities of 14C radiolabel were recovered from lipids, protein and CO2. Glucose incorporation into glycogen increased linearly over 6 h and showed saturation kinetics with respect to exogenous glucose concentration.

Insulin and glucagon secretory responses to arginine, glucagon, and theophylline during perifusion of human fetal islet-like cell clusters.

The secretory responsiveness of human fetal pancreatic endocrine cells was studied by perifusion of cultured islet-like cell clusters (ICC). ICC were obtained from 7 fetuses at 13-15 weeks gestation and 21 fetuses at 17-22 weeks gestation. The ICC were challenged with glucose (20 mmol/L), arginine (10 mmol/L), glucagon (1.4 mumol/L), and theophylline (10 mmol/L) combined with zero, low (2 mmol/L), or high (20 mmol/L) glucose. At 13-15 weeks, glucose and arginine enhanced insulin release in some experiments, whereas glucagon and theophylline were always potent stimuli (mean response, 4-fold regardless of the glucose concentration). At 17-22 weeks, both glucose alone (20 mmol/L) and arginine (10 mmol/L, with 2 mmol/L glucose) induced a small (1.4- to 1.5-fold) increase in insulin release. When arginine was combined with 20 mmol/L glucose, the response was potentiated to become a 2.3-fold increase. In contrast, glucagon was equally effective in 2 and 20 mmol/L glucose (2.9- and 2.6-fold responses, respectively) and produced a half-maximal response even in the absence of glucose. In this age range the most potent stimulus for insulin release was clearly theophylline. The effect of theophylline was also remarkably independent of the glucose concentration of the perifusate (5.6-, 8.1-, and 8.6-fold responses at 0, 2, and 20 mmol/L glucose, respectively). Glucagon release from the ICC of the 17- to 22-week-old fetuses was low (mean basal glucagon release, 2.9; insulin, 24.8 fmol/100 ICC/min). Glucagon release was not affected by 20 mmol/L glucose, but was stimulated by arginine and theophylline. These findings suggest that in the fetal pancreas, in contrast to the adult organ, insulin release results from elevation of intracellular cAMP concentrations (by glucagon or theophylline) relatively independent of the exogenous glucose concentration. Therefore, glucagon may have an important role in regulating insulin release during the early development of human fetal B-cells.

THE ROLE OF GLUCOSE AND INSULIN IN THE EFFECT OF ETHANOL ON PROTEIN SYNTHESIS IN ISOLATED RAT HEPATOCYTES

The incorporation of 14C-valine into liver protein was studied in isolated rat liver parenchymal cells. Various glucose levels in the incubation media did not affect the rate of 14C-valine incorporation into proteins. The insulin stimulated incorporation of 14C-valine into proteins was also unaffected by the various glucose levels. Ethanol decreased the incorporation of 14C-valine into liver proteins, affecting stationary and export proteins to the same extent. This inhibitory action of ethanol on valine incorporation was reversed by increasing exogenous glucose concentrations. The combination of insulin and high glucose level totally prevented the ethanol inhibition.

Glucose ameliorates the depletion of NADPH by paraquat in rat lung slices

Paraquat-stimulated NADPH depletion in rat lung slices is responsive to exogenous glucose concentration. Lung slices incubated with 11 mM glucose and 10 −4 M paraquat had a 40% lower NADPH/NADP + ratio than did control lung slices. Incubation with no added glucose and 10 −5 M paraquat caused a 41% decrease in NADPH/NADP +. With paraquat at 10 −5 M, glucose at 1.1, 5.5, 11, or 22 mM increased NADPH/NADP + ratios in a concentration-dependent manner until, at 22 mM glucose, the effect of paraquat was prevented. The sum of NADP + plus NADPH was only 60% of control with 10 −5 M paraquat and no glucose. However, with any concentration of glucose from 1.1 to 22 mM, the total was 92% of control. The results indicate that glucose may be beneficial in preventing paraquat-mediated NADPH depletion in rat lung slices.