Studies on the mechanism of L-leucine- and ?-ketoisocaproic acid ? Induced insulin release from perifused isolated pancreatic islets

Panten, U.; Christians, Julian K.; Kriegstein, E von; Poser, W.; Hasselblatt, A.

doi:10.1007/bf01219672

Cited by 53 publications

(32 citation statements)

References 9 publications

(10 reference statements)

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“…An increase in the extent of reduction of nicotinamide nucleotides in intact perifused islets of Langerhans was observed when the concentration of glucose in the perifusion medium was increased from 3 to 20mM (Panten et al, 1973). Such changes have been correlated with rates of insulin release under various conditions (Panten et al, 1973(Panten et al, , 1974. However, with the technique used, it was not possible ascertain the cellular location and identity of the reduced nicotinamide nucleotides.…”

mentioning

confidence: 95%

Effects of glucose on the cytosolic ration of reduced/oxidized nicotinamide-adenine dinucleotide phosphate in rat islets of Langerhans

Ashcroft¹,

Christie²

1979

Biochemical Journal

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The maximal extractable activity of 'malic' enzyme (EC 1.1.1.40) in rat islets of Langerhans was similar to that reported for liver. Thus 'malic' enzyme may catalyse a near-equilibrium reaction in the cytosol of islets of Langerhans. Measurements of islet content of malate and pyruvate, the metabolite substrate and product of 'malic' enzyme, were therefore used to calculate the cytosolic ratio of [NADPH]/[NADP+]. This ratio was higher in islets incubated with 20mM-glucose than in islets incubated with 2mM-glucose.

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confidence: 95%

Effects of glucose on the cytosolic ration of reduced/oxidized nicotinamide-adenine dinucleotide phosphate in rat islets of Langerhans

Ashcroft¹,

Christie²

1979

Biochemical Journal

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“…KIC is an endogenous substrate of the Krebs' cycle arising from the oxidative deamination of leucine. When applied externally, KIC permeates the plasmalemma and the mitochondrial membrane, thereby providing direct activation of the Krebs cycle and enhancing ATP production (45,46); the subsequent rise in the cytosolic ATP/ADP ratio is the proposed mechanism by which KIC inhibits K-ATP channels, stimulates the electrical activity, and elicits insulin release in a manner entirely similar to glucose (47). In this study, stimulation of the cells was provided by adding 30 mM KIC to the perifusion solution for specified periods; the pH i and the [Ca 2ϩ ] i were recorded from single cells which have been double-labeled with BCECF and fura-2. ]…”

Section: Effect Of Kic On the Ph I And [Ca 2ϩmentioning

confidence: 99%

Multiphasic Action of Glucose and -Ketoisocaproic Acid on the Cytosolic pH of Pancreatic -Cells

Salgado

Silva

Santos

et al. 1996

Journal of Biological Chemistry

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Glucose stimulation raises the pH i of pancreatic ␤-cells, but the underlying mechanisms are not well understood. We have now investigated the acute effects of metabolizable (glucose and the mitochondrial substrate ␣-ketoisocaproic acid, KIC) and nonmetabolizable (high K ؉ and the K-ATP channel blocker tolbutamide) insulin secretagogues on the pH i of pancreatic ␤-cells isolated from normal mice, as assessed by BCECF fluorescence from single cells or islets in the presence of external bicarbonate. The typical acute effect of glucose (22-30 mM) on the pH i was a fast alkalinization of approximately 0.11 unit, followed by a slower acidification. The relative expression of the alkalinizing and acidifying components was variable, with some cells and islets displaying a predominant alkalinization, others a predominant acidification, and others yet a mixed combination of the two. ] i , but the amplitude of the initial alkalinization was about twice as large for KIC relative to glucose. It is concluded that the acute effect of glucose on the pH i of pancreatic ␤-cells is biphasic. While the initial cytosolic alkalinization is an immediate consequence of the activation of H ؉ -consuming metabolic steps in the mitochondria, the secondary acidification appears to originate from enhanced Ca 2؉ turnover in the cytoplasm. The degree of coupling between glucose metabolism and Ca 2؉ influx as well as the relative efficacies of these processes determines whether the acute pH i response of a ␤-cell (or of a tightly coupled multicellular system such as an islet of Langerhans) is predominantly an alkalinization, an acidification, or a mixed proportion of the two.Pancreatic ␤-cells are endocrine cells specialized in the synthesis and secretion of insulin. Physiological release of the hormone is the result of a complex sequence of biophysical and biochemical events, involving entry of glucose through the GLUT-2 transporter, metabolic degradation of glucose to yield ATP, inhibition of ATP-sensitive K ϩ (K-ATP) channels following a rise in the cytosolic concentration of the nucleotide, membrane depolarization, activation of voltage-sensitive Ca 2ϩ channels, rises in the cytosolic free Ca 2ϩ concentration ([Ca 2ϩ

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“…Effects on K ATP Channel Activity by L-Leucine and 2-Oxopentanoate-Several studies have described insulinotrophic effects of L-leucine (3,20,21). Because of the blocking effect of ␣-ketoisocaproate on the K ATP channel, we also investigated whether the precursor amino acid, L-leucine, had direct effects on the channel in excised patches.…”

Section: Atp-dependent Kmentioning

confidence: 99%

“…1 An increase in mitochondrial metabolism plays an important role in the response to glucose and several other fuel secretagogues. Among other fuel secretagogues, the deamination product of the amino acid L-leucine, ␣-ketoisocaproate, is of particular interest since it is exclusively metabolized in mitochondria (3,4). Accordingly, several studies have shown that ␣-ketoisocaproate stimulates insulin secretion (3,4), initiates electrical activity (5), and inhibits the ␤-cell K ATP channel in intact cells monitored in the cell-attached configuration of the patch-clamp technique (6 -8).…”

mentioning

confidence: 99%

“…Among other fuel secretagogues, the deamination product of the amino acid L-leucine, ␣-ketoisocaproate, is of particular interest since it is exclusively metabolized in mitochondria (3,4). Accordingly, several studies have shown that ␣-ketoisocaproate stimulates insulin secretion (3,4), initiates electrical activity (5), and inhibits the ␤-cell K ATP channel in intact cells monitored in the cell-attached configuration of the patch-clamp technique (6 -8). The fact that metabolism of ␣-ketoisocaproate is confined to the mitochondria indicates that a product in Krebs cycle is involved in modulation of channel activity.…”

mentioning

confidence: 99%

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Direct Inhibition of the Pancreatic β-Cell ATP-regulated Potassium Channel by α-Ketoisocaproate

Bränström

Efendić

Berggren

et al. 1998

Journal of Biological Chemistry

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The ATP-regulated potassium (K ATP ) channel plays an essential role in the control of insulin release from the pancreatic ␤-cell. In the present study we have used the patch-clamp technique to study the direct effects of ␣-ketoisocaproate on the K ATP channel in isolated patches and intact pancreatic ␤-cells. In excised inside-out patches, the activity of the K ATP channel was dose-dependently inhibited by ␣-ketoisocaproate, half-maximal concentration being approximately 8 mM. The blocking effect of ␣-ketoisocaproate was fully reversible. Stimulation of channel activity by the addition of ATP/ADP (ratio 1) did not counteract the inhibitory effect of ␣-ketoisocaproate. In the presence of the metabolic inhibitor sodium azide, ␣-ketoisocaproate was still able to inhibit single channel activity in excised patches and to block whole cell K ATP currents in intact cells. No effect of ␣-ketoisocaproate could be obtained on either the large or the small conductance Ca 2؉ -regulated K ؉ channel. Enzymatic treatment of the patches with trypsin prevented the inhibitory effect of ␣-ketoisocaproate. Based on these observations, it is unlikely that the blocking effect of ␣-ketoisocaproate is due to an unspecific effect on K ؉ channel pores. Leucine, the precursor of ␣-ketoisocaproate, did not affect K ATP channel activity in excised patches. Our findings are compatible with the view that ␣-ketoisocaproate not only affects the ␤-cell stimulus secretion coupling by generation of ATP but also by direct inhibition of the K ATP channel.

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Studies on the mechanism of L-leucine- and ?-ketoisocaproic acid ? Induced insulin release from perifused isolated pancreatic islets

Cited by 53 publications

References 9 publications

Effects of glucose on the cytosolic ration of reduced/oxidized nicotinamide-adenine dinucleotide phosphate in rat islets of Langerhans

Effects of glucose on the cytosolic ration of reduced/oxidized nicotinamide-adenine dinucleotide phosphate in rat islets of Langerhans

Multiphasic Action of Glucose and -Ketoisocaproic Acid on the Cytosolic pH of Pancreatic -Cells

Direct Inhibition of the Pancreatic β-Cell ATP-regulated Potassium Channel by α-Ketoisocaproate

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