Energy Requirements for Insulin Release from Rat Pancreas<i>in Vitro</i>

Aleyassine, H.

doi:10.1210/endo-87-1-84

Cited by 31 publications

(15 citation statements)

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“…Given that this is an energy-dependent process (21), it is not surprising that metabolic inhibitors dramatically reduce insulin release (22)(23)(24)(25)(26)(27). However, such inhibitors have more profound effects on the ␤-cell, because the cell's recognition of glucose as a secretory stimulus also depends on metabolism of the glucose (28).…”

Section: Discussionmentioning

confidence: 99%

Glucose Metabolism and Pulsatile Insulin Release From Isolated Islets

Westerlund

Bergsten²

2001

Diabetes

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T he circulating insulin concentration displays regular oscillations in normal human subjects (1). Disturbances of these oscillations are an early sign in the development of type 2 diabetes (2,3). Such alterations may lead to insulin resistance and glucose intolerance by downregulation of insulin receptors (4). The plasma insulin oscillations have been attributed to the pulsatile release of the hormone from the pancreas (5), a process that requires coordinated secretion from the pancreatic islets (6).When the ambient glucose concentration is raised, ␤-cell metabolism is stimulated (7). The resulting increase in the ATP/ADP ratio decreases the permeability of the ATP-sensitive K ϩ (K ATP ) channels and depolarizes the cell (8). Subsequent influx of Ca 2ϩ through voltage-dependent channels triggers the exocytosis of insulin granules (9). ATP produced by metabolism also plays an important role in providing energy for secretion by recruitment and priming of insulin granules for exocytosis (10). Impaired glucose metabolism in pancreatic ␤-cells has been implicated in the development of the disturbed plasma insulin pattern seen in type 2 diabetes (11). Support for this idea has been obtained from altered plasma insulin patterns in patients with mutations in genes coding for glycolytic enzymes, such as phosphofructokinase and glucokinase and mitochondrial tRNA (12)(13)(14)(15)(16)(17).In the present study, we attempted to determine the importance of glycolytic and mitochondrial metabolism for pulsatile insulin release by measuring insulin secretion and [Ca 2ϩ ] i from individual pancreatic islets exposed to metabolic inhibitors at basal and stimulatory glucose concentrations. RESEARCH DESIGN AND METHODS Materials.Reagents of analytical grade and deionized water were used. Collagenase, HEPES, and bovine serum albumin (fraction V) were obtained from Boehringer Mannheim (Mannheim, Germany). Antimycin A, iodoacetamide (IAA), 2,4-dinitrophenol (DNP), tetramethylbenzidine, and insulinperoxidase were obtained from Sigma (St. Louis, MO). The rat insulin standard was obtained from Novo Nordisk (Bagsvaerd, Denmark). IgGcertified microtiter plates were purchased from Nunc (Roskilde, Denmark). The insulin antibodies were raised in guinea pigs. Preparation and culture of islets. Pancreatic islets were collagenaseisolated from ob/ob mice taken from a local colony (18). For the insulin experiments, freshly isolated islets were perifused in a medium supplemented with 1 mg/ml albumin and containing (in mmol/l) 125 NaCl, 5.9 KCl, 1.2 MgCl 2 , 1.3 CaCl 2 , and 25 HEPES, titrated to pH 7.4 with NaOH. For the [Ca 2ϩ ] i experiments, the islets were cultured overnight in the presence of 5.5 mmol/l glucose in RPMI 1640 supplemented with 10% fetal calf serum, and the Ca 2ϩ concentration of the perifusion medium was 2.6 mmol/l. Measurements of insulin release. The kinetics of insulin release were studied essentially as described previously (6). A single islet was placed in a temperature-controlled (37°C) 10-l chamber and perifused with med...

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Section: Discussionmentioning

confidence: 99%

Glucose Metabolism and Pulsatile Insulin Release From Isolated Islets

Westerlund

Bergsten²

2001

Diabetes

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“…This unusual characteristic is probably linked to the fact that glucose has to be metabolized by B cells to induce insulin release (1)(2)(3)(4)(5). It has long been known that ATP is necessary for insulin release (38), but whether its role is permissive or regulatory has proved much more difficult to establish. It is also not easy to define the respective roles of adenine and guanine nucleotides because they normally vary in parallel.…”

Section: Discussionmentioning

confidence: 99%

Concentration Dependence and Time Course of the Effects of Glucose on Adenine and Guanine Nucleotides in Mouse Pancreatic Islets

Detimary¹,

Berghe

Henquin³

1996

Journal of Biological Chemistry

129

110

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Changes in the ATP:ADP ratio in pancreatic B cells may participate in the regulation of insulin secretion by glucose. Here, we have investigated the possible role of guanine nucleotides. Mouse islets were incubated in a control medium (when K ؉ -ATP channels are the major site of regulation) or in a high K ؉ medium (when glucose modulates the effectiveness of cytosolic Ca 2؉ on exocytosis). Glucose induced a concentration-dependent (0 -20 mM) increase in GTP and a decrease in GDP in both types of medium, thus causing a progressive rise of the GTP:GDP ratio. ATP and ADP levels were 4 -5-fold higher but varied in a similar way as those of guanine nucleotides. Insulin secretion was inversely correlated with ADP and GDP levels and positively correlated with the ATP:ADP and GTP:GDP ratios between 6 and 20 mM glucose in control medium and between 0 and 20 mM glucose in high K ؉ medium. The increases in the GTP: GDP and ATP:ADP ratios induced by a rise of glucose were faster than the decreases induced by a fall in glucose, but the changes of both ratios were again parallel. In conclusion, glucose causes large, concentration-dependent changes in guanine as well as in adenine nucleotides in islet cells. This raises the possibility that both participate in the regulation of nutrient-induced insulin secretion.The regulation of pancreatic B cell function differs from that of other secretory cells in that the control of insulin secretion does not depend on the binding of the major physiological stimulator, glucose, to a receptor, but on its metabolism within B cells (reviewed in Refs. 1-5). It is now widely accepted that this metabolism generates several signals that close ATP-sensitive K ϩ channels (K ϩ -ATP channels) 1 in the plasma membrane. This closure (hereafter referred to as the "primary mechanism" of control) leads to membrane depolarization with subsequent opening of voltage-dependent Ca 2ϩ channels, Ca 2ϩ influx, rise in cytoplasmic free Ca 2ϩ concentration ([Ca 2ϩ ] i ), and eventual triggering of insulin secretion (4 -9). A "second mechanism" of control by glucose exists, which also depends on changes in metabolism (10 -12). It does not involve a further change in [Ca 2ϩ ] i but an increase in the effectiveness of Ca 2ϩ on its intracellular targets (12). Despite numerous studies, the nature of the signals that link the acceleration of metabolism to the closure of K ϩ -ATP channels and to the increase in Ca 2ϩ action has only partially been elucidated. Purine nucleotides clearly stand out as potential candidates.The popular hypothesis that variations in the cytosolic concentrations or ratio of adenine nucleotides are involved in the primary mechanism of control by glucose rests primarily on the fact that K ϩ channels, which control the B cell membrane potential, are regulated by intracellular ATP and ADP (6,8,9,13). Although this hypothesis has long been disputed (reviewed in Ref. 14), our demonstration of a correlation between insulin release and the ATP:ADP ratio in islets incubated in the presence of...

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“…Extensive studies have been performed to differentiate which of the above molecular mechanisms might be the basis of the permissive action of glucose on the P-cells (11,17,(25)(26)(27)(28)(29), whereas analogous studies of the glucose modulation of a-cell function are scanty (2,30 FIGURE 6 Relationship between insulin and glucagon in the first phase and the second phase of release above basal secretion rates caused by 15 mM amino acid mixture and increasing concentrations of glucose (see Table II). …”

Section: Discussionmentioning

confidence: 99%

Glucose Modulation of Amino Acid-Induced Glucagon and Insulin Release in the Isolated Perfused Rat Pancreas

Pagliara¹,

Stillings²,

Hover³

et al. 1974

J. Clin. Invest.

118

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A B S T R A C T Interactions between glucose and argiRline and a mixture of 20 amino acids found in normal rat serum were studied in the isolated perfused rat pancreas of normal rats, with release of immunoreactive glucagon and insulin as parameters. Secretion of both pancreatic hormones was low during the steady state, whether glucose (5 mMA) was included in the perfusion medium or not. This glucose concentration significantly stimulated insulin release twofold and resulted in an 80% inhibition of basal glucagon release. Arginine and the amino acid mixture were potent stimulants of both hormones. Secretion of both hormones followed identical biphasic response patterns after addition of arginine or the amino acid mixture. However, stimulation of insulin release occurred only when glucose was included, whereas both phases of glucagon release were elicited in the absence of glucose and markedly reduced in its presence. The dose-dependency curves of hormone release due to arginine on one hand and the amino acid mixture on the other differed substantially: with arginine, release of insulin and glucagon was linear between a concentration of 0.3 and 20 mM. In contrast, the amino acid mixture resulted in half-maximal release for both hormones between a concentration of 3 and 4.5 mAM, and maximal release between 6 and 8 mAM. The dose-dependencies of glucose modulation of a-and P-cell activity were also different: when the amino acid mixture was maintained at 15 mMI and glucose varied (0-6.25 mM), no insulin release occurred until glucose was above 2.5 mM, whereas incremental inhibition of glucagon occurred through the complete dose range. It was also observed that glucose inhibition of amino acid-stimulated glucagon reThis wdvork was presented in part at the meeting of the lease was dissociated from glucose-dependent increase of insulin release. These studies indicate that: (a) the a-cell, like the P-cell, secretes at a low basal rate; (b) hypoglycemia per se is a weak stimulus for glucagon secretion compared to the high efficacy of a physiologic amino acid mixture; (c) glucose plays opposite roles in the mechanisms leading to amino acid-induced hormone release from the a-and P-cells, functioning as an inhibitor in the first case and a permissive agent in the second, and (d) the data are compatible with the postulated existence of glucose and amino acid receptors in both the a-and P-cells.

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Energy Requirements for Insulin Release from Rat Pancreasin Vitro

Cited by 31 publications

References 0 publications

Glucose Metabolism and Pulsatile Insulin Release From Isolated Islets

Glucose Metabolism and Pulsatile Insulin Release From Isolated Islets

Concentration Dependence and Time Course of the Effects of Glucose on Adenine and Guanine Nucleotides in Mouse Pancreatic Islets

Glucose Modulation of Amino Acid-Induced Glucagon and Insulin Release in the Isolated Perfused Rat Pancreas

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