Differences between mouse and rat pancreatic islets: succinate responsiveness, malic enzyme, and anaplerosis

2002 ◽  
Vol 283 (2) ◽  
pp. E302-E310 ◽  
Author(s):  
Michael J. MacDonald
Keyword(s):  
Citric Acid ◽  
Pancreatic Islets ◽  
Insulin Release ◽  
Malic Enzyme ◽  
Citric Acid Cycle ◽  
Acetyl Coa ◽  
Acid Cycle ◽  
Rat Islets ◽  
Rat Pancreatic Islets ◽  
Mouse Islets

Succinic acid methyl esters are potent insulin secretagogues in rat pancreatic islets, but they do not stimulate insulin release in mouse islets. Unlike rat and human islets, mouse islets lack malic enzyme and, therefore, are unable to form pyruvate from succinate-derived malate for net synthesis of acetyl-CoA. Dimethyl-[2,3-14C]succinate is metabolized in the citric acid cycle in mouse islets to the same extent as in rat islets, indicating that endogenous acetyl-CoA condenses with oxaloacetate derived from succinate. However, without malic enzyme, the net synthesis from succinate of the citric acid cycle intermediates citrate, isocitrate, and α-ketoglutarate cannot occur. Glucose and other nutrients that augment α-ketoglutarate formation are secretagogues in mouse islets with potencies similar to those in rat islets. All cycle intermediates can be net-synthesized from α-ketoglutarate. Rotenone, an inhibitor of site I of the electron transport chain, inhibits methyl succinate-induced insulin release in rat islets even though succinate oxidation forms ATP at sites II and III of the respiratory chain. Thus generating ATP, NADH, and anaplerosis of succinyl-CoA plus the four-carbon dicarboxylic acids of the cycle and its metabolism in the citric acid cycle is insufficient for a fuel to be insulinotropic; it must additionally promote anaplerosis of α-ketoglutarate or two intermediates interconvertible with α-ketoglutarate, citrate, and isocitrate.

Perspective: emerging evidence for signaling roles of mitochondrial anaplerotic products in insulin secretion

2005 ◽  
Vol 288 (1) ◽  
pp. E1-E15 ◽  
Author(s):  
Michael J. MacDonald ◽  
Leonard A. Fahien ◽  
Laura J. Brown ◽  
Noaman M. Hasan ◽  
Julian D. Buss ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Citric Acid ◽  
Insulin Release ◽  
Citric Acid Cycle ◽  
Electrical Potential ◽  
Glycolytic Flux ◽  
Β Cell ◽  
Acetyl Coa ◽  
Acid Cycle ◽  
Atp Production

The importance of mitochondrial biosynthesis in stimulus secretion coupling in the insulin-producing β-cell probably equals that of ATP production. In glucose-induced insulin secretion, the rate of pyruvate carboxylation is very high and correlates more strongly with the glucose concentration the β-cell is exposed to (and thus with insulin release) than does pyruvate decarboxylation, which produces acetyl-CoA for metabolism in the citric acid cycle to produce ATP. The carboxylation pathway can increase the levels of citric acid cycle intermediates, and this indicates that anaplerosis, the net synthesis of cycle intermediates, is important for insulin secretion. Increased cycle intermediates will alter mitochondrial processes, and, therefore, the synthesized intermediates must be exported from mitochondria to the cytosol (cataplerosis). This further suggests that these intermediates have roles in signaling insulin secretion. Although evidence is quite good that all physiological fuel secretagogues stimulate insulin secretion via anaplerosis, evidence is just emerging about the possible extramitochondrial roles of exported citric acid cycle intermediates. This article speculates on their potential roles as signaling molecules themselves and as exporters of equivalents of NADPH, acetyl-CoA and malonyl-CoA, as well as α-ketoglutarate as a substrate for hydroxylases. We also discuss the “succinate mechanism,” which hypothesizes that insulin secretagogues produce both NADPH and mevalonate. Finally, we discuss the role of mitochondria in causing oscillations in β-cell citrate levels. These parallel oscillations in ATP and NAD(P)H. Oscillations in β-cell plasma membrane electrical potential, ATP/ADP and NAD(P)/NAD(P)H ratios, and glycolytic flux are known to correlate with pulsatile insulin release. Citrate oscillations might synchronize oscillations of individual mitochondria with one another and mitochondrial oscillations with oscillations in glycolysis and, therefore, with flux of pyruvate into mitochondria. Thus citrate oscillations may synchronize mitochondrial ATP production and anaplerosis with other cellular oscillations.

scholarly journals Differential effects of Ca2+-calmodulin on adenylate cyclase activity cyclase activity in mouse and rat pancreatic islets

1982 ◽  
Vol 206 (1) ◽  
pp. 97-102 ◽  
Author(s):  
P Thams ◽  
K Capito ◽  
C J Hedeskov
Keyword(s):  
Adenylate Cyclase ◽  
Pancreatic Islets ◽  
Specific Inhibitor ◽  
Particulate Fraction ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Rat Islets ◽  
Rat Pancreatic Islets ◽  
Mouse Islets

The effects of Ca2+-calmodulin on adenylate cyclase activity in EGTA-washed, 27000 g particulate fractions of mouse and rat pancreatic islets were studied. Ca2+ (10 microM)-calmodulin (1 microM) stimulated adenylate cyclase activity 53.1 +/- 5.2 (N = 6)% in the particulate fraction of rat islets. Trifluoperazine (50 microM), a specific inhibitor of calmodulin, inhibited the Ca2+-calmodulin activation of the adenylate cyclase activity of this fraction of rat islets. These results confirm previous reports dealing with Ca2+-Calmodulin and rat islet adenylate cyclase [Valverde, Vandermeers. Anjaneyulu & Malaisse (1979) Science 206, 225-227; Sharp, Wiedenkeller, Kaelin, Siegel & Wollheim (1980) Diabetes 29, 74-77]. In contrast, however, Ca2+ (1-100 microM)-calmodulin (1-10 microM) did not stimulate the adenylate cyclase activity in the EGTA-washed particulate fraction of mouse islets, and trifluoperazine (50 microM) did not inhibit the adenylate cyclase activity of this fraction of mouse islets, although some remaining calmodulin [0.18 +/- 0.05 (n = 3) microgram/mg of protein] could be demonstrated. GTP (10 microM) enhanced islet adenylate cyclase activity considerably, but did not confer any sensitivity towards Ca2+-calmodulin on mouse islet adenylate cyclase. The results question the role of calmodulin in the Ca2+-dependent rise in cyclic AMP evoked by glucose in pancreatic islets.

scholarly journals Probing the Origin of Acetyl-CoA and Oxaloacetate Entering the Citric Acid Cycle from the13C Labeling of Citrate Released by Perfused Rat Hearts

1997 ◽  
Vol 272 (42) ◽  
pp. 26117-26124 ◽  
Author(s):  
Blandine Comte ◽  
Geneviève Vincent ◽  
Bertrand Bouchard ◽  
Christine Des Rosiers
Keyword(s):  
Citric Acid ◽  
Citric Acid Cycle ◽  
Acetyl Coa ◽  
Acid Cycle ◽  
Rat Hearts ◽  
Perfused Rat Hearts

scholarly journals Metabolism of [3-13C]pyruvate and [3-13C]propionate in normal and ischaemic rat heart in vivo: 1H- and 13C-NMR studies

1995 ◽  
Vol 312 (1) ◽  
pp. 75-81 ◽  
Author(s):  
B Sumegi ◽  
B Podanyi ◽  
P Forgo ◽  
K E Kover
Keyword(s):  
Citric Acid ◽  
13C Nmr ◽  
Rat Heart ◽  
Citric Acid Cycle ◽  
Nmr Studies ◽  
Acetyl Coa ◽  
1H And 13C Nmr ◽  
Acid Cycle ◽  
Propionyl Carnitine

The oxidation of [3-13C]pyruvate and [3-13C]propionate was studied in vivo in infused rats. The infused [3-13C]pyruvate was quickly converted to [3-13C]lactate in the blood, and the [3-13C]lactate formed was well metabolized in both normoxic and ischaemic hearts. Large differences (200-600%) in the 13C enrichment of alanine (C-3) and acetyl-CoA (C-2) compared with lactate (C-3) were found in both normoxic and ischaemic hearts, suggesting that the extracellular [3-13C]lactate preferentially entered a region of the cytoplasm which specifically transfers the labelled pyruvate (formed from [3-13C]lactate) to the mitochondria. The highly enriched mitochondrial pyruvate gave high enrichment in alanine and acetyl-CoA, which was detected by 1H- and 13C-NMR spectroscopy. Ischaemia increased 13C incorporation into the main cytoplasmic lactate pool and decreased 13C incorporation into citric acid cycle intermediates, mainly decreasing the pyruvate anaplerosis. Isoprenaline-induced ischaemia of the heart caused only a slight decrease in pyruvate oxidation. In contrast to the decreased anaplerosis of pyruvate, the anaplerosis of propionate (and propionyl-carnitine) increased significantly in ischaemic hearts, which may contribute to the protective effect of propionyl-carnitine seen in ischaemia. In addition, we found that [3-13C]propionate preferentially labelled aspartate C-3 in rat heart, suggesting incomplete randomization of label in the succinyl-CoA-malate span of the citric acid cycle. These data show that proton observed 13C edited spectroscopic methods, i.e. heteronuclear spin-echo and the one-dimensional heteronuclear multiple quantum coherence sequence, can be successfully used to study heart metabolism in vivo.

Carbon Isotope Fractionation by Autotrophic Bacteria with Three Different C02 Fixation Pathways

1989 ◽  
Vol 44 (5-6) ◽  
pp. 397-402 ◽  
Author(s):  
Andrea Preuß ◽  
Rolf Schauder ◽  
Georg Fuchs ◽  
Willibald Stichler
Keyword(s):  
Citric Acid ◽  
Carbon Isotope ◽  
Isotope Fractionation ◽  
Citric Acid Cycle ◽  
Pentose Phosphate ◽  
Acetobacterium Woodii ◽  
Acetyl Coa ◽  
Acid Cycle ◽  
Acetyl Coa Pathway ◽  
Cell Carbon

Abstract Carbon isotope fractionation during autotrophic growth o f different bacteria which possess different autotrophic CO2 fixation pathways has been studied. 13C /12C -Ratios in the cell carbon of the following bacteria were determined (CO2 fixation pathway suggested or proven in paren­theses): Alkaligenes eutrophus (reductive pentose phosphate cycle), Desulfobacterium autotrophicum and Acetobacterium woodii (reductive acetyl-CoA pathway), Desulfobacter hydrogenophilus and Thermoproteus neutrophilus (reductive citric acid cycle). The Δδ13C values, which indicate the per mille deviation of the 13C content of cell carbon from that of the CO : used as the sole carbon source, range from - 10%° (reductive citric acid cycle) over - 26%° (reductive pentose phosphate cycle) to -36%° (reductive acetyl-CoA pathway). Acetate formed via the acetyl-CoA pathway by the acetogenic Acetobacterium woodii showed a Δδ13C = -40%°. These data are discussed in view of the different CO2 fixation reactions used by the bacteria and especially with regard to the isotopic composition of sedimentary carbon through time.

scholarly journals Functions of the Membrane-Associated and Cytoplasmic Malate Dehydrogenases in the Citric Acid Cycle ofEscherichia coli

2000 ◽  
Vol 182 (24) ◽  
pp. 6892-6899 ◽  
Author(s):  
Michel E. van der Rest ◽  
Christian Frank ◽  
Douwe Molenaar
Keyword(s):  
Citric Acid ◽  
Malic Enzyme ◽  
Citric Acid Cycle ◽  
Wild Type ◽  
Batch Cultures ◽  
Acid Cycle ◽  
E Coli ◽  
Link Type ◽  
Phosphoenolpyruvate Synthase ◽  
Rates Of Growth

ABSTRACT Oxidation of malate to oxaloacetate in Escherichia colican be catalyzed by two enzymes: the well-known NAD-dependent malate dehydrogenase (MDH; EC 1.1.1.37 ) and the membrane-associated malate:quinone-oxidoreductase (MQO; EC 1.1.99.16 ), encoded by the genemqo (previously called yojH). Expression of themqo gene and, consequently, MQO activity are regulated by carbon and energy source for growth. In batch cultures, MQO activity was highest during exponential growth and decreased sharply after onset of the stationary phase. Experiments with the β-galactosidase reporter fused to the promoter of the mqo gene indicate that its transcription is regulated by the ArcA-ArcB two-component system. In contrast to earlier reports, MDH did not repressmqo expression. On the contrary, MQO and MDH are active at the same time in E. coli. For Corynebacterium glutamicum, it was found that MQO is the principal enzyme catalyzing the oxidation of malate to oxaloacetate. These observations justified a reinvestigation of the roles of MDH and MQO in the citric acid cycle of E. coli. In this organism, a defined deletion of the mdh gene led to severely decreased rates of growth on several substrates. Deletion of the mqo gene did not produce a distinguishable effect on the growth rate, nor did it affect the fitness of the organism in competition with the wild type. To investigate whether in an mqo mutant the conversion of malate to oxaloacetate could have been taken over by a bypass route via malic enzyme, phosphoenolpyruvate synthase, and phosphenolpyruvate carboxylase, deletion mutants of the malic enzyme genessfcA and b2463 (coding for EC 1.1.1.38 and EC1.1.1.40 , respectively) and of the phosphoenolpyruvate synthase (EC2.7.9.2 ) gene pps were created. They were introduced separately or together with the deletion of mqo. These studies did not reveal a significant role for MQO in malate oxidation in wild-type E. coli. However, comparing growth of themdh single mutant to that of the double mutant containingmdh and mqo deletions did indicate that MQO partly takes over the function of MDH in an mdh mutant.

scholarly journals The regulation of glucose and pyruvate formation from glutamine and citric-acid-cycle intermediates in the kidney cortex of rats, dogs, rabbits and guinea pigs

1980 ◽  
Vol 188 (3) ◽  
pp. 741-748 ◽  
Author(s):  
M Watford ◽  
P Vinay ◽  
G Lemieux ◽  
A Gougoux
Keyword(s):  
Citric Acid ◽  
Guinea Pig ◽  
Guinea Pigs ◽  
Malic Enzyme ◽  
Citric Acid Cycle ◽  
Alternative Pathway ◽  
Lactate Production ◽  
Kidney Cortex ◽  
Acid Cycle ◽  
Pig Kidney

The suppression by 3-mercaptopicolinate of gluconeogenesis from glutamine or 2-oxoglutarate in rat or dog kidney tubules did not affect the amount of these substrates undergoing complete oxidation. Furthermore, 3-mercaptopicolinate caused an accumulation of lactate in dog tubules. 3-Mercaptopicolinate abolished both gluconeogenesis and substrate oxidation in tubules from rabbit and guinea-pig kidney. These results imply the presence of an alternative pathway to phosphoenolpyruvate carboxykinase/pyruvate kinase for the production of pyruvate from citric-acid-cycle intermediates in the kidney cortex of rats and dogs but not in that of rabbits or guinea pigs. Oxaloacetate decarboxylase (present in the kidney cortex of all four species) or ‘malic’ enzyme (present in rat and dog but absent in rabbit and guinea-pig kidney cortex) could function in this role. Our observations indicate that ‘malic’ enzyme is probably implicated in this phenomenon. The lactate production observed in dog tubules in the presence of 3-mercaptopicolinate can be suppressed when aspartate formation is inhibited by 2-amino-4-methoxy-trans-but-3-enoic acid. This suggests that the provision of cytosolic NADH from citric-acid-cycle intermediates is facilitated by accumulation of aspartate acting as a ‘sink’ for cytosolic oxaloacetate.

Secretagogue-induced [Ca2+]i changes in single rat pancreatic islets and correlation with simultaneously measured insulin release

1995 ◽  
Vol 15 (2) ◽  
pp. 177-185 ◽  
Author(s):  
F Martin ◽  
J A Reig ◽  
B Soria
Keyword(s):  
Pancreatic Islets ◽  
Insulin Release ◽  
Phorbol Esters ◽  
Late Phase ◽  
Transient Increase ◽  
Free Calcium ◽  
Second Phase ◽  
Rat Islets ◽  
Rat Pancreatic Islets ◽  
Pancreatic Islets Of Langerhans

ABSTRACT The effects of secretagogues (glucose, tolbutamide and phorbol esters) on simultaneously measured intracellular free calcium concentration ([Ca2+]i) and insulin release were studied in rat pancreatic islets of Langerhans. Stimulatory concentrations (11 mm) of glucose caused a transient [Ca2+]i increase followed by an almost flat second phase. Increasing glucose concentrations to 16·7 mm in steps caused a further increase in [Ca2+]i. In contrast with mouse islets, rat islets scarcely showed glucose-induced [Ca2+]i oscillations. Digital image analysis showed that [Ca2+]i changes occurred synchronously across the whole islet. As expected, simultaneously measured insulin release was biphasic with a clear second phase. This clearly indicated that in rat islets there is a lack of correlation between [Ca2+]i and insulin release. This was further explored using agents which separately promoted the first (tolbutamide, 200 μm) and second (phorbol-12-myristate-13-acetate; PMA; 5 nm) phases of insulin release. Tolbutamide induced a transient increase in [Ca2+]i paralleled by a transient increase in insulin release, whereas PMA induced a slow increase in insulin release without a clear change in [Ca2+]i. These results suggest that in rat islets the first phase of insulin release is calcium dependent, whereas the second phase is related to the activation of protein kinase C (PKC). However, the glucose-induced second phase of insulin release did not coincide with an increase in membrane-associated PKC activity. Other messengers may contribute to this late phase of insulin release.

scholarly journals Changes in the contents of adenine nucleotides and intermediates of glycolysis and citric acid cycle in flight muscle of the locust upon flight and their relationship to the control of the cycle

1979 ◽  
Vol 178 (1) ◽  
pp. 209-216 ◽  
Author(s):  
Andrew N. Rowan ◽  
Eric A. Newsholme
Keyword(s):  
Citric Acid ◽  
Citric Acid Cycle ◽  
Flight Muscle ◽  
Citrate Synthase ◽  
Adenine Nucleotides ◽  
Total Content ◽  
Acetyl Coa ◽  
Free Concentration ◽  
Acid Cycle ◽  
Early Stages

1. The contents of some intermediates of glycolysis, the citric acid cycle and adenine nucleotides have been measured in the freeze-clamped locust flight muscle at rest and after 10s and 3min flight. The contents of glucose 6-phosphate, pyruvate, alanine and especially fructose bisphosphate and triose phosphates increased markedly upon flight. The content of acetyl-CoA is decreased after 3min flight whereas that of acetylcarnitine is decreased markedly after 10s flight, but returns towards the resting value after 3min flight. The content of citrate is markedly decreased after both 10s and 3min flight, whereas that of isocitrate is changed very little after 10s and is increased by 50% after 3min. The content of oxaloacetate is very low in insect flight muscle and hence it was measured by a sensitive radiochemical assay. The content of oxaloacetate increased about 2-fold after 3min flight. A similar change was observed in the content of malate. The content of ATP decreased about 15%, whereas those of ADP and AMP increased about 2-fold after 3min flight. 2. Calculations based on O2 uptake of the intact insect indicate that the rate of the citric acid cycle must be increased >100-fold during flight. Consequently, if citrate synthase catalyses a non-equilibrium reaction, the activity of the enzyme must increase >100-fold during flight. However, changes in the concentrations of possible regulators of citrate synthase, oxaloacetate, acetyl-CoA and citrate (which is an allosteric inhibitor), are not sufficient to account for this change in activity. It is concluded that there may be much larger changes in the free concentration of oxaloacetate than are indicated by the changes in the total content of this metabolite or that other unknown factors must play an additional role in the regulation of citrate synthase activity. 3. The increased content of oxaloacetate could be produced via pyruvate carboxylase, which may be stimulated during the early stages of flight by the increased concentration of pyruvate. 4. The decreases in the concentrations of citrate and α-oxoglutarate indicate that isocitrate dehydrogenase and oxoglutarate dehydrogenase may be stimulated by factors other than their pathway substrates during the early stages of flight. 5. Calculated mitochondrial and cytosolic NAD+/NADH ratios are both increased upon flight. The change in the mitochondrial ratio indicates the importance of the intramitochondrial ATP/ADP concentration ratio in the regulation of the rate of electron transfer in this muscle.

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