AJP - Endo Email Content Delivery
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Am J Physiol Endocrinol Metab 292: E1201-E1206, 2007. First published December 26, 2006; doi:10.1152/ajpendo.00459.2006
0193-1849/07 $8.00
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
292/4/E1201    most recent
00459.2006v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via ISI Web of Science (1)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Wang, C.
Right arrow Articles by Ling, Z.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Wang, C.
Right arrow Articles by Ling, Z.

Glucagon-like peptide-1 stimulates GABA formation by pancreatic beta-cells at the level of glutamate decarboxylase

Chen Wang, Rui Mao, Mark Van De Casteele, Daniel Pipeleers, and Zhidong Ling

Diabetes Research Center, Brussels Free University-VUB, and Juvenile Diabetes Research Foundation Center for beta-Cell Therapy in Diabetes, Brussels, Belgium

Submitted 31 August 2006 ; accepted in final form 19 December 2006


   ABSTRACT
TOP
 ABSTRACT
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Pancreatic beta-cells are the major extraneural site of glutamate decarboxylase expression (GAD). During culture of isolated beta-cells, the GAD product {gamma}-aminobutyrate (GABA) is rapidly released in the medium, independently of insulin. It is considered as a possible mediator of beta-cell influences on {alpha}-cells, acinar cells, and/or infiltrating lymphocytes. In this perspective, we investigated the regulation of GABA release by rat beta-cells during a 24-h culture period. Glucose was previously reported to inhibit GABA release by diverting cellular GABA to mitochondrial breakdown through activation of GABA transferase (GABA-T). In the present study, glucagon-like peptide-1 (GLP-1) was shown to stimulate GABA formation at the level of GAD, its effect being suppressed by the GAD inhibitor allylglycine and remaining unaltered by the GABA-T inhibitor {gamma}-vinyl-GABA. The stimulatory action of GLP-1 is cAMP dependent, being reproduced by the adenylate cyclase activator forskolin and the cAMP analog N6-benzoyladenosine-3',5'-cAMP and inhibited by a PKA inhibitor. It is dependent on protein synthesis and associated with an increased expression of GAD67 but not GAD65. The GLP-1-induced stimulation of GAD activity in beta-cells can elevate medium GABA levels in conditions of glucose-driven intracellular GABA breakdown and thus maintain GABA-mediated beta-cell influences on neighboring cells.

forskolin; {gamma}-aminobutyric acid; cyclic adenosine 3',5'-monophosphate

PANCREATIC beta-CELLS are the major site of extraneural glutamate decarboxylase (GAD) expression (16, 19, 33, 45). The enzyme catalyzes the formation of {gamma}-aminobutyric acid (GABA) from glutamate, which can be derived from extracellular glutamine. The existence of GABA transferase (GABA-T) (17) can channel part of produced GABA to the mitochondrial tricarboxylic acid cycle for further metabolism (45), thus filling in a nutrient function for extracellular glutamine. Most nonmetabolized GABA is rapidly released in the extracellular medium where it may act as autocrine/paracrine regulator (4, 5, 21, 41, 42, 50). GABAA receptors have been recognized on pancreatic {alpha}-cells and were correlated with a GABA-induced inhibition of glucagon release (40, 50). They were also found on pancreatic acinar cells mediating a GABA amplification of cholecystokinin-induced enzyme release (34, 35). Interestingly, GABA release from beta-cells may also interact with infiltrating T cells and suppress their activity, thus providing protection against autoimmune damage (46). Functional GABAA receptors were identified on T lymphocytes (1, 46), and GABA was found to downregulate in vitro effector T cell responses to beta-cell antigens (46). Administration of GABA also delayed disease progression in diabetes-prone mice (2, 46). Although further work is needed on the (patho)physiological role of GABA release from pancreatic beta-cells, it can be useful, in this context, to identify its physiological stimuli and their action mechanism. In previous work on rat beta-cells, we (43, 48, 51) have shown that glucose suppresses GABA release by activating the GABA-T-mediated GABA shuttle into the mitochondria. This effect was counteracted by glucagon and glucagon-like peptide-1 (GLP-1), which were found to stimulate GABA release (51). GLP-1 and its analogs may thus serve not only as amplifiers of glucose-induced insulin release (9, 11, 23, 29) but also as facilitators of GABA release in the pancreas and thus of local GABA-mediated effects, a combination that is distinct from the glucose effects. The present study examines the mechanism through which GLP-1 exerts this effect.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Preparation and culture of rat pancreatic beta-cells. Adult male Wistar rats were bred according to Belgian regulation of animal welfare. Isolated islets and purified beta-cells were prepared as described (37). Briefly, pancreatic islets were isolated by collagenase (Sigma) digestion and dissociated into single cells in calcium-free medium containing trypsin (Boehringer, Mannheim, Germany) and deoxyribonuclease (DNase, Boehringer). Single beta-cells were purified by autofluorescence-activated sorting using cellular light-scatter and flavin adenine dinucleotide (FAD) autofluorescence as discriminating parameters (37).

Freshly isolated beta-cells were reaggregated for 2 h in a rotatory shaking incubator at 37°C (26) and then statically cultured for 16 h in Ham's F-10 medium (GIBCO UK) supplemented with 2 mM glutamine (Sigma), 6.1 mM glucose, 0.5% (wt/vol) charcoal-extracted BSA (Sigma), 0.075 g/l penicillin, and 0.1 g/l streptomycin. After this preculture period, beta-cell aggregates were cultured for 24 h in glutamate-free Ham's F-10 medium containing 0.5% charcoal-extracted BSA, 0.075 g/l penicillin, and 0.1 g/l streptomycin, at 10 mM glucose and 2 mM glutamine, with one or more of the following agents: {gamma}-vinyl-GABA (GVG, Sigma), allylglycine (Sigma), verapamil (10 µM, Knoll, Germany), cycloheximide (CHX, Sigma), GLP-1-(7–36) amide (10 nM GLP-1, Sigma), forskolin (20 µM FK, Sigma), N6-benzoyladenosine-3',5'-cAMP (6-Bnz-cAMP; Biolog Life Science Institute), 8-(4-chlorophenylthio)-2'-O-methyladenosine-3',5'-cAMP (8-CPT-Me-cAMP; Biolog Life Science Institute), 8-bromoadenosine-5',5'-cyclic monophosphorothioate, Rp-isomer (100 µM Rp-8-Br-cAMP, Biolog Life Science Institute). At the end of culture, cells and media were collected for GABA and insulin determinations and, in selected experiments, for measuring GAD protein expression by Western blotting.

GABA and insulin assays. GABA was measured by isocratic elution and electrochemical detection after precolumn derivatization with o-phthaldialdehyde and microbore liquid chromatography separation (44) in filtered media and cell extracts following sonication in PBS with 0.1% BSA and centrifugation (49). Insulin was assayed in culture medium and in acetic acid extracts of cells (37).

GAD protein expression. Protein expression was analyzed by Western blotting as previously described (26). Briefly, cells were lysed in 10–20 µl of RIPA buffer containig a cocktail of protease inhibitors, sonicated in 30–40 µl of SDS-gel sample buffer, size fractionated on 10% SDS-polyacrylamide gels, and electroblotted onto nitrocellulose membranes. The membranes were then incubated with primary antibodies diluted in blocking buffer. Mouse anti-GAD67 antibody (Chemicon International, Temecula, CA) and rabbit anti-GAD65 antibody (a gift from Prof. A. Lernmark, Univ. of Washington, Seattle, WA) were used at 1:1,000 dilution. Horseradish peroxidase-linked IgG was used as secondary antibody, and peroxidase activity was detected by ECL (Amersham, Buckinghamshire, UK). Band intensity was quantified by Scion Image software and expressed in arbitrary units of optical density.

Data expression and statistical analysis. Insulin and GABA were expressed as picomoles per 103 cells at start of the experiments. Data represent means ± SE of n independent experiments. Statistical significance of differences was determined using either Student's t-test or ANOVA.


   RESULTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 GRANTS
 REFERENCES
 
Sustained exposure to GLP-1 and FK stimulates GABA release by beta-cells via cAMP-dependent and calcium-independent process. The presence of GLP-1 (10 nM) during 24-h culture of rat beta-cells increased both medium and cellular GABA content at 10 mM glucose (Table 1). This was also the case with the adenylate cyclase (AC) activator FK (20 µM;10), and with the cAMP analog 6-Bnz-cAMP (450 µM), a protein kinase A (PKA) activator (7), but not with the exchange protein directly activated by cAMP (EPAC) activator 8-CPT-2Me-cAMP [500 µM (12); Table 1]. Addition of the PKA inhibitor Rp-8-Br-cAMP [100 µM (20)] completely prevented GLP-1- and 6-Bnz-cAMP-induced GABA release and inhibited the FK effect by 41% (Table 1). On the other hand, suppression of calcium uptake, as induced by the calcium channel blocker verapamil (10 µM) at 0.3 mM calcium, did not suppress GLP-1- and FK-induced GABA release (data not shown), indicating that calcium influx was not essential for GLP-1-induced GABA production.


View this table:
[in this window]
[in a new window]

  		Table 1. Effect of GLP-1 and other cAMP generators on cellular and medium GABA levels in absence and presence of PKA inhibitor

 
GLP-1 and FK increase GABA release by stimulating GAD-dependent formation of GABA and not by reducing GABA-T-dependent GABA breakdown. The GLP-1- and FK-induced GABA release is associated with an increased cellular GABA content and is thus indicative of an elevated accumulation of GABA. Such an effect can result from a reduction in intracellular GABA breakdown or from an increase in GABA formation. To distinguish both mechanisms, measurements were conducted following culture with the GABA-T inhibitor GVG (27) or with the GAD inhibitor allylglycine (3).

In control cells, addition of the GABA-T inhibitor GVG increased basal GABA release twofold, indicating that this enzyme, under the selected culture conditions, is responsible for shunting at least 50% of formed GABA into mitochondrial metabolism. When the cells were cultured with the GAD inhibitor allylglycine at 5 mM, GABA release was reduced by 60%, which indicates that influences on cellular GAD activity can be detected through changes in extracellular GABA levels. We did not test whether GABA release was further suppressed by higher allylglycine concentrations.

Addition of GVG did not interfere with the GLP-1 and FK effects and increased medium and cellular GABA levels in both conditions as it did in the control cells (Table 2). The GLP-1 and FK effects are therefore not the result of a reduced GABA catabolism. On the other hand, allylglycine suppressed both GLP-1- and FK-induced increases in medium and cellular GABA content (Table 3 and Fig. 1). The dose dependency of this inhibition was demonstrated for FK (Fig. 1) and found to occur without altering FK-induced stimulation of insulin release (Fig. 1). These data suggest that GLP-1 and FK stimulate GABA formation at the level of GAD activity. This is further supported by the observation that the FK-induced increase was not seen in the absence of extracellular glutamine, which is the precursor of glutamate, the substrate for GAD (Table 4). On the other hand, absence of glutamine did not interfere with the insulin-stimulatory effect FK (data not shown), indicating that this agent still activated cAMP-mediated effects in the beta-cells.


View this table:
[in this window]
[in a new window]

  		Table 2. Effect of GABA-transferase inhibitor GVG on GLP-1 and forskolin-induced GABA production

 

View this table:
[in this window]
[in a new window]

  		Table 3. Effect of GAD inhibitor allylglycine on GLP-1-induced GABA production

 

Figure 1
View larger version (17K):
[in this window]
[in a new window]

  		Fig. 1. Effect of glutamate decarboxylase (GAD) inhibitor allylglycine on forskolin (FK)-induced GABA and insulin content in medium and cells. Rat beta-cells were preincubated for 2 h in absence or presence of allylglycine (allylgly) and then cultured for 8 h with or without FK (20 µM). Left: medium content GABA (top) or insulin (bottom); right: cellular GABA (top) or insulin (bottom). Data represent means ± SE of 4 independent experiments. Statistical significance of differences is calculated by Student's t-test. *P < 0.01 vs. corresponding control (without FK).

 

View this table:
[in this window]
[in a new window]

  		Table 4. Effect of glutamine on forskolin-induced GABA production

 
To examine whether the FK effect on GABA formation resulted from an increased glutamine uptake or/and increased glutaminase-mediated formation of glutamate from glutamine, we assessed its influence in a medium where glutamine was substituted by dimethyl glutamate, which is known to be membrane permeable. In this condition, the FK-induced stimulation of GABA accumulation remained present, which is in line with an effect at the level of GAD activity rather than at the level of substrate provision (Table 5).


View this table:
[in this window]
[in a new window]

  		Table 5. Effect of glutamine and glutamate on foskolin-induced GABA production

 
GLP-1- and FK-induced increase in GABA formation is associated with rise in GAD67 protein expression. Culture for 24 h with GLP-1 or FK increases expression of GAD67 protein but not of GAD65 protein (Fig. 2). This effect was suppressed by the translation inhibitor cycloheximide (0.5 µg/ml), which also suppressed the stimulatory effect of GLP-1 on GABA formation (Fig. 2). In the control condition, addition of cycloheximide also led to a lower expression of GAD67 protein but not of GAD65 (Fig. 2). This effect was associated with a reduction in GABA formation (Fig. 2).


Figure 2
View larger version (38K):
[in this window]
[in a new window]

  		Fig. 2. GAD65/67 protein expression and GABA release by rat beta-cells following 24-h culture in presence of GLP-1 (left) or FK (right; 20 µM) with or without cycloheximide (CHX, 0.5 µg/ml). Data represent means ± SE of 4–5 independent experiments. Statistical significance of differences was calculated by Student's t-test. *P < 0.01 vs. corresponding control.

 

   DISCUSSION
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
GRANTS
 REFERENCES
 
The present study confirms that GLP-1 stimulates GABA release by pancreatic beta-cells (51). As in previous work (48) the amount released in the medium reflects the net rate of GABA production by the cells. The stimulatory effect of GLP-1 appears mediated by an increased cAMP formation as it was reproduced by the adenyl cyclase activator forskolin. It involves stimulation of PKA and not of EPAC, since it was also induced by the selective PKA activator 6-Bnz-cAMP, whereas no effect was seen with the selective EPAC activator 8-CPT-Me-cAMP; moreover, it was completely prevented by a specific PKA inhibitor. In contrast to GLP-1-mediated stimulation of insulin release (28, 39), GLP-1-induced GABA release occurs independently of calcium influx; we have not examined whether it involves an intracellular calcium mobilization. Our data support the view that GABA is not coreleased with insulin and thus varies independently of the secretory activity (30, 32, 43). This dissociation was first observed for glucose, which was found to decrease GABA release while stimulating insulin release (22, 43, 48, 51). The opposing effects of glucose and cAMP generators on GABA release contrast with their synergistic action on insulin release (36, 38, 47). The functional consequence of this opposing action is presently unclear, in the first place because the physiological role of GABA released by the beta-cells has not yet been clarified. The present data do, however, indicate that GLP-1 not only amplifies glucose effects on beta-cells but also counteracts one of them. It is conceivable that GLP-1-induced GABA formation helps maintaining extracellular GABA levels while glucose diverts GABA into mitochondrial activity. This GLP-1 action may then result in GABA-mediated effects on glucagon release (18, 40, 50) and/or on acinar cell function (35). It could also provide protection when islets become infiltrated by T lymphocytes (46) and thus add a rationale for testing GLP-1 as agent in the prevention of type 1 diabetes (2, 31, 46).

Glucose had been found to suppress GABA release by stimulating the GABA-shunting enzyme GABA-T, thus shifting intracellular GABA into mitochondrial breakdown (48). This effect depends on glucose-driven mitochondrial activity (51). The GLP-1 and forskolin stimulation of GABA release did not result from an opposing effect on this enzyme: the effects of both compounds were indeed not affected by the presence of the GABA-T inhibitor GVG. On the other hand, their effect was suppressed when GAD activity was inhibited by allylglycine, an inhibitor of GAD (3, 15), indicating that it resulted from a stimulated GAD activity. Measurement of GAD activity in cellular extracts yielded similar results in control and in GLP-1- or forskolin-pretreated cell preparations and thus failed to provide direct evidence for such a mechanism. It is, however, likely that GAD activity in the extract is not representative of the activity in intact cells where the major part of the enzyme might be present under an inactive form as is the case in neurons (6, 13, 24).

Although the present data indicate that the medium GABA levels vary markedly with the activity of cellular GAD, it is so far unclear to what extent they reflect the activity of the GAD65 or of the GAD67 isoform or of both. The two isoforms are known to occur in rat beta-cells (14, 25) and were also demonstrated in the present study. Expression of GAD67, but not of GAD65, was significantly reduced by 24-h culture in the presence of the translation inhibitor cycloheximide, indicating its shorter half-life (8). The parallel reduction in GABA release is not necessarily a sign for its contribution to the released GABA as the latter may also depend on some as yet unidentified protein with rapid turnover. It is nevertheless interesting to note that both the GLP-1- and forskolin-induced GABA releases were associated with an increased expression of the GAD67 but not of the GAD65 protein and that cycloheximide completely suppressed the stimulated GABA release and GAD67 expression.

In conclusion, GLP-1 increases GABA release by rat beta-cells as a result of a stimulated activity of glutamate decarboxylase. This GLP-1 effect appears calcium independent and is mediated by cyclic AMP involving protein synthesis. It is associated with an increased expression of GAD67 but not of GAD65.


   GRANTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
REFERENCES
 
This study was supported by grants from the Belgian Federal Government (Federale Diensten Wetenschapsbeleid-Interuniversity Attraction Pole P5/17), the Juvenile Diabetes Research Foundation (no. 4-2001-434), and the Belgian Fund Scientific Research-Fonds Wetenschappelijk Onderzoek (no. G0357.03).


   ACKNOWLEDGMENTS
 
We thank Ria Berckmans for help with the microbore liquid chromatography and Rene De Proft and Hongyun Li for technical assistance. Part of this work was presented at the Islet Study Group Meeting 2005, Alicante, Spain.


   FOOTNOTES
 

Address for reprint requests and other correspondence: Z. Ling, Diabetes Research Center, Brussels Free University-VUB Laarbeeklaan 103, B-1090 Brussels, Belgium, (e-mail: Zhidong.Ling{at}vub.ac.be)

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.


   REFERENCES
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 

  1. Alam S, Laughton DL, Walding A, Wolstenholme AJ. Human peripheral blood mononuclear cells express GABAA receptor subunits. Mol Immunol 43: 1432–1442, 2006.[CrossRef][ISI][Medline]
  2. Beales PE, Hawa M, Williams AJ, Albertini MC, Giorgini A, Pozzilli P. Baclofen, a {gamma}-aminobutyric acid-b receptor agonist, delays diabetes onset in the non-obese diabetic mouse. Acta Diabetol 32: 53–56, 1995.[CrossRef][ISI][Medline]
  3. Brandao ML, Di Scala G, Bouchet MJ, Schmitt P. Escape behavior produced by the blockade of glutamic acid decarboxylase (GAD) in mesencephalic central gray or medial hypothalamus. Pharmacol Biochem Behav 24: 497–501, 1986.[CrossRef][ISI][Medline]
  4. Braun M, Wendt A, Buschard K, Salehi A, Sewing S, Gromada J, Rorsman P. GABAB receptor activation inhibits exocytosis in rat pancreatic beta-cells by G-protein-dependent activation of calcineurin. J Physiol 559: 397–409, 2004.[Abstract/Free Full Text]
  5. Brice NL, Varadi A, Ashcroft SJ, Molnar E. Metabotropic glutamate and GABA(B) receptors contribute to the modulation of glucose-stimulated insulin secretion in pancreatic beta-cells. Diabetologia 45: 242–252, 2002.[CrossRef][ISI][Medline]
  6. Chen CH, Battaglioli G, Martin DL, Hobart SA, Colon W. Distinctive interactions in the holoenzyme formation for two isoforms of glutamate decarboxylase. Biochim Biophys Acta 1645: 63–71, 2003.[Medline]
  7. Christensen AE, Selheim F, de Rooij J, Dremier S, Schwede F, Dao KK, Martinez A, Maenhaut C, Bos JL, Genieser HG, Doskeland SO. cAMP analog mapping of Epac1 and cAMP kinase. Discriminating analogs demonstrate that Epac and cAMP kinase act synergistically to promote PC-12 cell neurite extension. J Biol Chem 278: 35394–35402, 2003.[Abstract/Free Full Text]
  8. Christgau S, Schierbeck H, Aanstoot HJ, Aagaard L, Begley K, Kofod H, Hejnaes K, Baekkeskov S. Pancreatic beta-cells express two autoantigenic forms of glutamic acid decarboxylase, a 65-kDa hydrophilic form and a 64-kDa amphiphilic form which can be both membrane-bound and soluble. J Biol Chem 266: 21257–21264, 1991.[Abstract/Free Full Text]
  9. Cunningham BA, Richard AM, Dillon JS, Daley JT, Civelek VN, Deeney JT, Yaney GC, Corkey BE, Tornheim K. Glucagon-like peptide 1 and fatty acids amplify pulsatile insulin secretion from perifused rat islets. Biochem J 369: 173–178, 2003.[CrossRef][ISI][Medline]
  10. de Souza NJ, Dohadwalla AN, Reden J. Forskolin: a labdane diterpenoid with antihypertensive, positive inotropic, platelet aggregation inhibitory, and adenylate cyclase activating properties. Med Res Rev 3: 201–219, 1983.[ISI][Medline]
  11. Drucker DJ. Glucagon-like peptides. Diabetes 47: 159–69, 1998.[Abstract]
  12. Enserink JM, Christensen AE, de Rooij J, van Triest M, Schwede F, Genieser HG, Doskeland SO, Blank JL, Bos JL. A novel Epac-specific cAMP analogue demonstrates independent regulation of Rap1 and ERK. Nat Cell Biol 4: 901–906, 2002.[CrossRef][ISI][Medline]
  13. Erlander MG, Tillakaratne NJ, Feldblum S, Patel N, Tobin AJ. Two genes encode distinct glutamate decarboxylases. Neuron 7: 91–100, 1991.[CrossRef][ISI][Medline]
  14. Faulkner-Jones BE, Cram DS, Kun J, Harrison LC. Localization and quantitation of expression of two glutamate decarboxylase genes in pancreatic beta-cells and other peripheral tissues of mouse and rat. Endocrinology 133: 2962–2972, 1993.[Abstract]
  15. Fernandez-Pascual S, Mukala-Nsengu-Tshibangu A, Martin Del Rio R, Tamarit-Rodriguez J. Conversion into GABA ({gamma}-aminobutyric acid) may reduce the capacity of L-glutamine as an insulin secretagogue. Biochem J 379: 721–729, 2004.[CrossRef][ISI][Medline]
  16. Garry DJ, Appel NM, Garry MG, Sorenson RL. Cellular and subcellular immunolocalization of L-glutamate decarboxylase in rat pancreatic islets. J Histochem Cytochem 36: 573–580, 1988.[Abstract]
  17. Garry DJ, Coulter HD, McIntee TJ, Wu JY, Sorenson RL. Immunoreactive GABA transaminase within the pancreatic islet is localized in mitochondria of the B-cell. J Histochem Cytochem 35: 831–836, 1987.[Abstract]
  18. Gaskins HR, Baldeon ME, Selassie L, Beverly JL. Glucose modulates {gamma}-aminobutyric acid release from the pancreatic beta-TC6 cell line. J Biol Chem 270: 30286–30289, 1995.[Abstract/Free Full Text]
  19. Gilon P, Bertrand G, Loubatieres-Mariani MM, Remacle C, Henquin JC. The influence of {gamma}-aminobutyric acid on hormone release by the mouse and rat endocrine pancreas. Endocrinology 129: 2521–2529, 1991.[Abstract]
  20. Gjertsen BT, Mellgren G, Otten A, Maronde E, Genieser HG, Jastorff B, Vintermyr OK, McKnight GS, Doskeland SO. Novel (Rp)-cAMPS analogs as tools for inhibition of cAMP-kinase in cell culture. Basal cAMP-kinase activity modulates interleukin-1beta action. J Biol Chem 270: 20599–20607, 1995.[Abstract/Free Full Text]
  21. Gu XH, Kurose T, Kato S, Masuda K, Tsuda K, Ishida H, Seino Y. Suppressive effect of GABA on insulin secretion from the pancreatic beta-cells in the rat. Life Sci 52: 687–694, 1993.[CrossRef][ISI][Medline]
  22. Hayashi M, Yamada H, Uehara S, Morimoto R, Muroyama A, Yatsushiro S, Takeda J, Yamamoto A, Moriyama Y. Secretory granule-mediated cosecretion of L-glutamate and glucagon triggers glutamatergic signal transmission in islets of Langerhans. J Biol Chem 278: 1966–1974, 2003.[Abstract/Free Full Text]
  23. Holz GG. New insights concerning the glucose-dependent insulin secretagogue action of glucagon-like peptide-1 in pancreatic beta-cells. Horm Metab Res 36: 787–794, 2004.[CrossRef][ISI][Medline]
  24. Kaufman DL, Houser CR, Tobin AJ. Two forms of the {gamma}aminobutyric acid synthetic enzyme glutamate decarboxylase have distinct intraneuronal distributions and cofactor interactions. J Neurochem 56: 720–723, 1991.[CrossRef][ISI][Medline]
  25. Kim J, Richter W, Aanstoot HJ, Shi Y, Fu Q, Rajotte R, Warnock G, Baekkeskov S. Differential expression of GAD65 and GAD67 in human, rat, and mouse pancreatic islets. Diabetes 42: 1799–1808, 1993.[Abstract]
  26. Ling Z, Van de Casteele M, Eizirik DL, Pipeleers DG. Interleukin-1betainduced alteration in a beta-cell phenotype can reduce cellular sensitivity to conditions that cause necrosis but not to cytokine-induced apoptosis. Diabetes 49: 340–345, 2000.[Abstract]
  27. Lippert B, Metcalf BW, Jung MJ, Casara P. 4-amino-hex-5-enoic acid, a selective catalytic inhibitor of 4-aminobutyric-acid aminotransferase in mammalian brain. Eur J Biochem 74: 441–445, 1977.[ISI][Medline]
  28. Lu M, Wheeler MB, Leng XH, Boyd AE 3rd. The role of the free cytosolic calcium level in beta-cell signal transduction by gastric inhibitory polypeptide and glucagon-like peptide I(7–37). Endocrinology 132: 94–100, 1993.[Abstract]
  29. Mojsov S, Weir GC, Habener JF. Insulinotropin: glucagon-like peptide I (7–37) co-encoded in the glucagon gene is a potent stimulator of insulin release in the perfused rat pancreas. J Clin Invest 79: 616–619, 1987.[ISI][Medline]
  30. Nagamatsu S, Watanabe T, Nakamichi Y, Yamamura C, Tsuzuki K, Matsushima S. {alpha}-Soluble N-ethylmaleimide-sensitive factor attachment protein is expressed in pancreatic beta-cells and functions in insulin but not {gamma}-aminobutyric acid secretion. J Biol Chem 274: 8053–8060, 1999.[Abstract/Free Full Text]
  31. Nakagawa T, Yokozawa T, Kim HJ, Shibahara N. Protective effects of {gamma}-aminobutyric acid in rats with streptozotocin-induced diabetes. J Nutr Sci Vitaminol (Tokyo) 51: 278–282, 2005.[Medline]
  32. Ohara-Imaizumi M, Nakamichi Y, Ozawa S, Katsuta H, Ishida H, Nagamatsu S. Mastoparan stimulates GABA release from MIN6 cells: relationship between SNARE proteins and mastoparan action. Biochem Biophys Res Commun 289: 1025–1030, 2001.[CrossRef][ISI][Medline]
  33. Okada Y, Taniguchi H, Schimada C. High concentration of GABA and high glutamate decarboxylase activity in rat pancreatic islets and human insulinoma. Science 194: 620–622, 1976.[Abstract/Free Full Text]
  34. Park HS, Park HJ. Effects of {gamma}-aminobutyric acid on secretagogue-induced exocrine secretion of isolated, perfused rat pancreas. Am J Physiol Gastrointest Liver Physiol 279: G677–G682, 2000.[Abstract/Free Full Text]
  35. Park YD, Cui ZY, Wu G, Park HS, Park HJ. {Gamma}-aminobutyric acid secreted from islet beta-cells modulates exocrine secretion in rat pancreas. World J Gastroenterol 12: 3026–3030, 2006.[ISI][Medline]
  36. Parkes DG, Pittner R, Jodka C, Smith P, Young A. Insulinotropic actions of exendin-4 and glucagon-like peptide-1 in vivo and in vitro. Metabolism 50: 583–589, 2001.[CrossRef][ISI][Medline]
  37. Pipeleers DG, in't Veld PA, Van de Winkel M, Maes E, Schuit FC, Gepts W. A new in vitro model for the study of pancreatic A and B cells. Endocrinology 117: 806–816, 1985.[Abstract]
  38. Pipeleers DG, Schuit FC, in't Veld PA, Maes E, Hooghe-Peters EL, Van de Winkel M, Gepts W. Interplay of nutrients and hormones in the regulation of insulin release. Endocrinology 117: 824–833, 1985.[Abstract]
  39. Rajan AS, Hill RS, Boyd AE 3rd. Effect of rise in cAMP levels on Ca2+ influx through voltage-dependent Ca2+ channels in HIT cells. Second-messenger synarchy in beta-cells. Diabetes 38: 874–880, 1989.[Abstract]
  40. Rorsman P, Berggren PO, Bokvist K, Ericson H, Mohler H, Ostenson CG, Smith PA. Glucose-inhibition of glucagon secretion involves activation of GABAA-receptor chloride channels. Nature 341: 233–236, 1989.[CrossRef][Medline]
  41. Satin LS, Kinard TA. Neurotransmitters and their receptors in the islets of Langerhans of the pancreas: what messages do acetylcholine, glutamate, and GABA transmit? Endocrine 8: 213–223, 1998.[CrossRef][ISI][Medline]
  42. Shi Y, Kanaani J, Menard-Rose V, Ma YH, Chang PY, Hanahan D, Tobin A, Grodsky G, Baekkeskov S. Increased expression of GAD65 and GABA in pancreatic beta-cells impairs first-phase insulin secretion. Am J Physiol Endocrinol Metab 279: E684–E694, 2000.[Abstract/Free Full Text]
  43. Smismans A, Schuit F, Pipeleers D. Nutrient regulation of {gamma}-aminobutyric acid release from islet beta-cells. Diabetologia 40: 1411–1415, 1997.[CrossRef][ISI][Medline]
  44. Smolders I, Sarre S, Michotte Y, Ebinger G. The analysis of excitatory, inhibitory and other amino acids in rat brain microdialysates using microbore liquid chromatography. J Neurosci Methods 57: 47–53, 1995.[CrossRef][ISI][Medline]
  45. Sorenson RL, Garry DG, Brelje TC. Structural and functional considerations of GABA in islets of Langerhans. Beta-cells and nerves. Diabetes 40: 1365–1374, 1991.[Abstract]
  46. Tian J, Lu Y, Zhang H, Chau CH, Dang HN, Kaufman DL. {Gamma}aminobutyric acid inhibits T cell autoimmunity and the development of inflammatory responses in a mouse type 1 diabetes model. J Immunol 173: 5298–5304, 2004.[Abstract/Free Full Text]
  47. Trimble ER, Halban PA, Wollheim CB, Renold AE. Functional differences between rat islets of ventral and dorsal pancreatic origin. J Clin Invest 69: 405–413, 1982.[ISI][Medline]
  48. Wang C, Kerckhofs K, Van de Casteele M, Smolders I, Pipeleers D, Ling Z. Glucose inhibits GABA release by pancreatic beta-cells through an increase in GABA shunt activity. Am J Physiol Endocrinol Metab 290: E494–E499, 2006.[Abstract/Free Full Text]
  49. Wang C, Ling Z, Pipeleers D. Comparison of cellular and medium insulin and GABA content as markers for living beta-cells. Am J Physiol Endocrinol Metab 288: E307–E313, 2005.[Abstract/Free Full Text]
  50. Wendt A, Birnir B, Buschard K, Gromada J, Salehi A, Sewing S, Rorsman P, Braun M. Glucose inhibition of glucagon secretion from rat {alpha}-cells is mediated by GABA released from neighboring beta-cells. Diabetes 53: 1038–1045, 2004.[Abstract/Free Full Text]
  51. Winnock F, Ling Z, De Proft R, Dejonghe S, Schuit F, Gorus F, Pipeleers D. Correlation between GABA release from rat islet beta-cells and their metabolic state. Am J Physiol Endocrinol Metab 282: E937–E942, 2002.[Abstract/Free Full Text]




This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
292/4/E1201    most recent
00459.2006v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via ISI Web of Science (1)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Wang, C.
Right arrow Articles by Ling, Z.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Wang, C.
Right arrow Articles by Ling, Z.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Visit Other APS Journals Online
Copyright © 2007 by the American Physiological Society.