In the rat islets γ-aminobutyric acid (GABA) is produced by the β-cells and at least the α-cells express the GABAA receptors (GABAA channels). for α5 or ε subunits. The large quantity of the GABAA receptor subunits detected suggests that a number of GABAA receptor subtypes are created in the islets. The single-channel and tonic currents were enhanced by pentobarbital and inhibited by the GABAA receptor antagonist SR-95531. The single-channel Glucosamine sulfate conductance ranged from 24 to 105 pS. Whether the single-channel conductance is related to subtypes of the GABAA receptor or variable interstitial GABA concentrations remains to be decided. Our results reveal that GABA is an extracellular signaling molecule in rat pancreatic islets and reaches concentration levels that activate GABAA receptors around the glucagon-releasing α-cells. Introduction The pancreatic islets consist of four major cell types: the glucagon-secreting α-cells the insulin-secreting β-cells the somatostatin-secreting δ-cells and the polypeptide-producing PP-cells. In addition to the hormones the cells release small molecules that may take action in an auto or paracrine manner  . Gamma-aminobutyric acid (GABA) is an extracellular transmission molecule in the islets    . GABA is usually formed by the enzyme glutamate decarboxylase (GAD) which catalyses the formation of GABA from glutamate and is located both in the cytoplasm and in synaptic-like vesicles     . Once released GABA is Pten usually thought to take action in an auto and paracrine manner around the islet cells to modulate hormone secretion       . GABA activates ionotropic GABAA and metabotropic GABAB receptors in the plasma membrane of the islet cells   . In the rat islet only the α-cells express the GABAA receptors (GABAA channels)  whereas in human pancreatic islets the α β and δ-cells all have GABAA receptors  . There are numerous subtypes of GABAA receptors whereas only one GABAB receptor has been described so far . The GABAA receptors are pentameric. The subunits are grouped into eight families Glucosamine sulfate (α1-6 β1-3 γ1-3 δ ε θ π ρ1-3) and the receptors generally contain at least 3 different types of subunits: 2 αs 2 βs and a third subunit-type. The physiological and pharmacological properties Glucosamine sulfate of the receptors are determined by the subunit-types that form the GABAA receptors . When GABA binds to the GABAA receptor a chloride-permeable ion channel is usually opened. The activation of GABAA channel is best analyzed in the central Glucosamine sulfate nervous system where the receptors evoke phasic (transient) and tonic (long-lasting) inhibition. Phasic activation is usually mediated by synaptic GABAA Glucosamine sulfate receptors and is triggered by the transient high concentration of GABA (～mM) released from your presynaptic terminal whereas tonic activation of the extrasynaptic receptors is usually evoked by the ambient GABA concentration present round the neuron . In the rat β-cells the vesicular release of GABA coincides with the release of the insulin made up of granules when the cell is usually exposed to high glucose activation  whereas the non-vesicular release of GABA appears to take place both in high and low glucose concentration . This raises the question of the mode of activation of the GABAA receptors in the pancreatic islet. So far most of the electrophysiological studies of GABAA receptors in pancreatic islet cells have been conducted on dispersed cells  or transfected cells overexpressing GABAA receptors  . These studies have therefore not resolved the mode of GABAA receptors activation in intact islets. One reason why physiological experiments have predominantly used dispersed cells is related to the difficulty of identifying the cell-types in intact islets. Here we have used the method of single-cell RT-PCR to distinguish the type of cell we recorded from. Our results show in intact rat pancreatic islets that interstitial GABA generates tonic currents in the α-cells when the islets are exposed to 20 mM glucose. The tonic current can be enhanced by pentobarbital and inhibited by SR-95531 both drugs specific for GABAA receptors. Materials and.