Microdetermination of Free Amino Acids in Pancreatic Islets Isolated from Obese‐Hyperglycemic Mice

Briel, G.; Gylfe, Erik; Hellman, Bo; Neuhoff, Volker

doi:10.1111/j.1748-1716.1972.tb05175.x

Cited by 58 publications

(24 citation statements)

References 21 publications

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“…In most cases, activation of GABA A R in neurons results in membrane hyperpolarisation as a consequence of an inward Cl -flux [3]. The concentrations of GABA and GAD and the density of GABA A R in pancreatic islets are comparable with those encountered in the central nervous system [4][5][6][7][8], suggesting that the GABA-GABA A R system plays a role in modulating islet endocrine functions. In the pancreas, GABA is primarily produced by insulin-secreting beta cells [9][10][11] and probably by the glucagon-containing alpha cells [9,12].…”

Section: Introductionmentioning

confidence: 75%

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Gamma-aminobutyric acid up- and downregulates insulin secretion from beta cells in concert with changes in glucose concentration

et al. 2006

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Aims/hypothesis: The role of gamma-aminobutyric acid (GABA) and A-type GABA receptors (GABA A Rs) in modulating islet endocrine function has been actively investigated since the identification of GABA and GABA A Rs in the pancreatic islets. However, the reported effects of GABA A R activation on insulin secretion from islet beta cells have been controversial. Methods: This study examined the hypothesis that the effect of GABA on beta cell insulin secretion is dependent on glucose concentration. Results: Perforated patchclamp recordings in INS-1 cells demonstrated that GABA, at concentrations ranging from 1 to 1,000 μmol/l, induced a transmembrane current (I GABA ) which was sensitive to the GABA A R antagonist bicuculline. The current-voltage relationship revealed that I GABA reversed at −42±2.2 mV, independently of glucose concentration. Nevertheless, the glucose concentration critically controlled the membrane potential (V M ), i.e., at low glucose (0 or 2.8 mmol/l) the endogenous V M of INS-1 cells was below the I GABA reversal potential and at high glucose (16.7 or 28 mmol/l), the endogenous V M of INS-1 cells was above the I GABA reversal potential. Therefore, GABA dose-dependently induced membrane depolarisation at a low glucose concentration, but hyperpolarisation at a high glucose concentration. Consistent with electrophysiological findings, insulin secretion assays demonstrated that at 2.8 mmol/l glucose, GABA increased insulin secretion in a dose-dependent fashion (p<0.05, n=7). This enhancement was blocked by bicuculline (p<0.05, n=4). In contrast, in the presence of 28 mmol/l glucose, GABA suppressed the secretion of insulin (p<0.05, n=5). Conclusions/interpretation: These findings indicate that activation of GABA A Rs in beta cells regulates insulin secretion in concert with changes in glucose levels.

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Section: Introductionmentioning

confidence: 75%

“…Previous studies [4][5][6][7][8] suggest that the pancreatic GABA-GABA A R system plays a role in modulating islet endocrine functions. However, the reported effects of GABA on insulin secretion from the beta cells have been controversial.…”

Section: Discussionmentioning

confidence: 99%

Gamma-aminobutyric acid up- and downregulates insulin secretion from beta cells in concert with changes in glucose concentration

et al. 2006

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“…The islets of Langerhans have long been known to contain GABA (33) and GAD (34), and both paracrine and intracellular roles have been proposed (1,13). The present study identifies an additional human GAD gene, GAD-2, that maps to the p11.2 to p13 region ofhuman chromosome 10 (Fig.…”

Section: Discussionmentioning

confidence: 99%

Cloning and primary structure of a human islet isoform of glutamic acid decarboxylase from chromosome 10.

Karlsen

Hagopian

Grubin

et al. 1991

Proc. Natl. Acad. Sci. U.S.A.

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157

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Glutamic acid decarboxylase (GAD; glutamate decarboxylase, L-glutamate 1-carboxy-lyase, EC 4.1.1.15), which catalyzes formation of gamma-aminobutyric acid from L-glutamic acid, is detectable in different isoforms with distinct electrophoretic and kinetic characteristics. GAD has also been implicated as an autoantigen in the vastly differing autoimmune disease stiff-man syndrome and insulin-dependent diabetes mellitus. Despite the differing GAD isoforms, only one type of GAD cDNA (GAD-1), localized to a syntenic region of chromosome 2, has been isolated from rat, mouse, and cat. Using sequence information from GAD-1 to screen a human pancreatic islet cDNA library, we describe the isolation of an additional GAD cDNA (GAD-2), which was mapped to the short arm of human chromosome 10. Genomic Southern blotting with GAD-2 demonstrated a hybridization pattern different from that detected by GAD-1. GAD-2 recognizes a 5.6-kilobase transcript in both islets and brain, in contrast to GAD-1, which detects a 3.7-kilobase transcript in brain only. The deduced 585-amino acid sequence coded for by GAD-2 shows less than 65% identity to previously published, highly conserved GAD-1 brain sequences, which show greater than 96% deduced amino acid sequence homology among the three species. The function of this additional islet GAD isoform and its importance as an autoantigen in insulin-dependent diabetes remain to be determined.

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“…Islets of Langerhans contain GABA, the enzymes that catalyze its biosynthesis (GAD) and metabolism (GABA transaminase), and GABA receptors at concentrations comparable with levels in the central nervous system (3)(4)(5)(6)(7). In particular, ␤-cells contain a much higher concentration of GABA than other types of islet cells.…”

mentioning

confidence: 99%

Vesicular Inhibitory Amino Acid Transporter Is Present in Glucagon-Containing Secretory Granules in αTC6 Cells, Mouse Clonal α-Cells, and α-Cells of Islets of Langerhans

et al. 2003

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Islets of Langerhans contain ␥-aminobutyrate (GABA) and may use it as an intercellular transmitter. In ␤-cells, GABA is stored in synaptic-like microvesicles and secreted through Ca 2؉ -dependent exocytosis. Vesicular inhibitory amino acid transporter (VIAAT), which is responsible for the storage of GABA and glycine in neuronal synaptic vesicles, is believed to be responsible for the storage and secretion of GABA in ␤-cells. . Islets of Langerhans contain GABA, the enzymes that catalyze its biosynthesis (GAD) and metabolism (GABA transaminase), and GABA receptors at concentrations comparable with levels in the central nervous system (3-7). In particular, ␤-cells contain a much higher concentration of GABA than other types of islet cells. In ␤-cells, GABA is stored in synaptic-like microvesicles (SLMVs), endocrine counterparts of neuronal synaptic vesicles, but not in insulin granules (8). ATP-dependent vesicular GABA transport activity has been detected in isolated SLMVs (9). Furthermore, ␤-cells and MIN6 cells (clonal ␤-cells) secrete GABA through Ca 2ϩ -dependent and -independent pathways (10 -14). Exogenous GABA has been shown to inhibit glucagon secretion by way of GABAA receptors on ␣-cells (15-17). These results indicate that ␤-cells are the major sites of GABA signal appearance in the islets and that GABA functions as a paracrine-like intercellular chemical transmitter that regulates islet function.Vesicular inhibitory amino acid transporter (VIAAT) is responsible for the storage of GABA and glycine in synaptic vesicles through active transport at the expense of ATP hydrolysis by a vacuolar proton pump (18,19). The cDNA encoding VIAAT has been cloned, and its primary amino acid sequence has been determined (19). Because VIAAT is a potential probe for GABA signal appearance in neurons, it can be supposed that islet cells, especially ␤-cells, express VIAAT. Very recently, it was found that islet cells actually contain VIAAT (20). Unexpectedly, however, immunohistochemical evidence obtained with antibodies against either the COOH-terminal or NH 2 -terminal region of VIAAT indicated that VIAAT immunoreactivity is predominantly present in nonϪ␤-cells and probably ␣-cells, although the precise localization of VIAAT at the cellular or subcellular level has not yet been determined (20).L-glutamate may also function as an intercellular messenger in the islets of Langerhans (21). We have shown that vesicular glutamate transporter (VGLUT), which is responsible for the vesicular storage of L-glutamate and thus a potential probe for L-glutamate signal appearance, is expressed in ␣-cells and is specifically associated with GABA, ␥-aminobutyrate; SLMV, synaptic-like microvesicle; VGLUT, vesicular glutamate transporter; VIAAT, vesicular inhibitory amino acid transporter.

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Microdetermination of Free Amino Acids in Pancreatic Islets Isolated from Obese‐Hyperglycemic Mice

Cited by 58 publications

References 21 publications

Gamma-aminobutyric acid up- and downregulates insulin secretion from beta cells in concert with changes in glucose concentration

Gamma-aminobutyric acid up- and downregulates insulin secretion from beta cells in concert with changes in glucose concentration

Cloning and primary structure of a human islet isoform of glutamic acid decarboxylase from chromosome 10.

Vesicular Inhibitory Amino Acid Transporter Is Present in Glucagon-Containing Secretory Granules in αTC6 Cells, Mouse Clonal α-Cells, and α-Cells of Islets of Langerhans

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