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GABAB-receptor activation inhibits exocytosis in rat pancreatic {beta}-cells by G-protein-dependent activation of calcineurin.

Braun, Matthias LU ; Wendt, Anna LU ; Buschard, Karsten; Salehi, Albert; Sewing, Sabine; Gromada, Jesper and Rorsman, Patrik LU (2004) In Journal of Physiology 559(2). p.397-409
Abstract
We have investigated the regulation of hormone secretion from rat pancreatic islets by the GABAB receptors (GABABRs). Inclusion of the specific GABABR antagonist CGP 55845 in the extracellular medium increased glucose-stimulated insulin secretion 1.6-fold but did not affect the release of glucagon and somatostatin. Conversely, addition of the GABABR agonist baclofen inhibited glucose-stimulated insulin secretion by ∼60%. Using RT-PCR, transcription of GABABR1a-c,f and GABABR2 subunits was detected in β-cells. Measurements of membrane currents and cell capacitance were applied to single β-cells to investigate the mechanisms by which GABABR activation inhibits insulin secretion. In perforated-patch measurements, baclofen inhibited exocytosis... (More)
We have investigated the regulation of hormone secretion from rat pancreatic islets by the GABAB receptors (GABABRs). Inclusion of the specific GABABR antagonist CGP 55845 in the extracellular medium increased glucose-stimulated insulin secretion 1.6-fold but did not affect the release of glucagon and somatostatin. Conversely, addition of the GABABR agonist baclofen inhibited glucose-stimulated insulin secretion by ∼60%. Using RT-PCR, transcription of GABABR1a-c,f and GABABR2 subunits was detected in β-cells. Measurements of membrane currents and cell capacitance were applied to single β-cells to investigate the mechanisms by which GABABR activation inhibits insulin secretion. In perforated-patch measurements, baclofen inhibited exocytosis elicited by 500-ms voltage-clamp depolarizations to 0 mV by ≤ 80% and voltage-gated Ca2+ entry by only ∼30%. Both effects were concentration-dependent with IC50 values of ∼2 μm. The inhibitory action of baclofen was abolished in the presence of CGP 55845. The ability of baclofen to suppress exocytosis was prevented by pre-treatment with pertussis toxin and by inclusion of GDPβS in the intracellular medium, and became irreversible in the presence of GTPγS as expected for a process involving inhibitory G-proteins (Gi/o-proteins). The inhibitory effect of baclofen resulted from activation of the serine/threonine protein phosphatase calcineurin and pre-treatment with cyclosporin A or intracellular application of calcineurin autoinhibitory peptide abolished the effect. Addition of baclofen had no effect on [Ca2+]i and electrical activity in glucose-stimulated β-cells. These data indicate that GABA released from β-cells functions as an autocrine inhibitor of insulin secretion in pancreatic islets and that the effect is principally due to direct suppression of exocytosis. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Journal of Physiology
volume
559
issue
2
pages
397 - 409
publisher
The Physiological Society
external identifiers
  • wos:000224038500005
  • scopus:4644278226
ISSN
1469-7793
DOI
10.1113/jphysiol.2004.066563
language
English
LU publication?
yes
id
7430279b-da12-4a84-8c2a-13ad0fb1d138 (old id 125989)
alternative location
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=15235087&dopt=Abstract
date added to LUP
2007-07-10 15:00:28
date last changed
2017-10-01 04:49:26
@article{7430279b-da12-4a84-8c2a-13ad0fb1d138,
  abstract     = {We have investigated the regulation of hormone secretion from rat pancreatic islets by the GABAB receptors (GABABRs). Inclusion of the specific GABABR antagonist CGP 55845 in the extracellular medium increased glucose-stimulated insulin secretion 1.6-fold but did not affect the release of glucagon and somatostatin. Conversely, addition of the GABABR agonist baclofen inhibited glucose-stimulated insulin secretion by ∼60%. Using RT-PCR, transcription of GABABR1a-c,f and GABABR2 subunits was detected in β-cells. Measurements of membrane currents and cell capacitance were applied to single β-cells to investigate the mechanisms by which GABABR activation inhibits insulin secretion. In perforated-patch measurements, baclofen inhibited exocytosis elicited by 500-ms voltage-clamp depolarizations to 0 mV by ≤ 80% and voltage-gated Ca2+ entry by only ∼30%. Both effects were concentration-dependent with IC50 values of ∼2 μm. The inhibitory action of baclofen was abolished in the presence of CGP 55845. The ability of baclofen to suppress exocytosis was prevented by pre-treatment with pertussis toxin and by inclusion of GDPβS in the intracellular medium, and became irreversible in the presence of GTPγS as expected for a process involving inhibitory G-proteins (Gi/o-proteins). The inhibitory effect of baclofen resulted from activation of the serine/threonine protein phosphatase calcineurin and pre-treatment with cyclosporin A or intracellular application of calcineurin autoinhibitory peptide abolished the effect. Addition of baclofen had no effect on [Ca2+]i and electrical activity in glucose-stimulated β-cells. These data indicate that GABA released from β-cells functions as an autocrine inhibitor of insulin secretion in pancreatic islets and that the effect is principally due to direct suppression of exocytosis.},
  author       = {Braun, Matthias and Wendt, Anna and Buschard, Karsten and Salehi, Albert and Sewing, Sabine and Gromada, Jesper and Rorsman, Patrik},
  issn         = {1469-7793},
  language     = {eng},
  number       = {2},
  pages        = {397--409},
  publisher    = {The Physiological Society},
  series       = {Journal of Physiology},
  title        = {GABAB-receptor activation inhibits exocytosis in rat pancreatic {beta}-cells by G-protein-dependent activation of calcineurin.},
  url          = {http://dx.doi.org/10.1113/jphysiol.2004.066563},
  volume       = {559},
  year         = {2004},
}