Limits...
γ-Aminobutyric acid (GABA) signalling in human pancreatic islets is altered in type 2 diabetes.

Taneera J, Jin Z, Jin Y, Muhammed SJ, Zhang E, Lang S, Salehi A, Korsgren O, Renström E, Groop L, Birnir B - Diabetologia (2012)

Bottom Line: The currents were enhanced by pentobarbital and inhibited by the GABA(A) receptor antagonist, SR95531.The effects of SR95531 on hormone release revealed that activation of GABA(A) channels (GABA(A) receptors) decreased both insulin and glucagon secretion.Interstitial GABA activates GABA(A) channels and GABA(B) receptors and effectively modulates hormone release in islets from type 2 diabetic and normoglycaemic individuals.

View Article: PubMed Central - PubMed

Affiliation: Department of Clinical Sciences, Lund University Diabetes Center, University Hospital Malmö, Lund University, Malmö, Sweden.

ABSTRACT

Aims/hypothesis: γ-Aminobutyric acid (GABA) is a signalling molecule in the interstitial space in pancreatic islets. We examined the expression and function of the GABA signalling system components in human pancreatic islets from normoglycaemic and type 2 diabetic individuals.

Methods: Expression of GABA signalling system components was studied by microarray, quantitative PCR analysis, immunohistochemistry and patch-clamp experiments on cells in intact islets. Hormone release was measured from intact islets.

Results: The GABA signalling system was compromised in islets from type 2 diabetic individuals, where the expression of the genes encoding the α1, α2, β2 and β3 GABA(A) channel subunits was downregulated. GABA originating within the islets evoked tonic currents in the cells. The currents were enhanced by pentobarbital and inhibited by the GABA(A) receptor antagonist, SR95531. The effects of SR95531 on hormone release revealed that activation of GABA(A) channels (GABA(A) receptors) decreased both insulin and glucagon secretion. The GABA(B) receptor antagonist, CPG55845, increased insulin release in islets (16.7 mmol/l glucose) from normoglycaemic and type 2 diabetic individuals.

Conclusions/interpretation: Interstitial GABA activates GABA(A) channels and GABA(B) receptors and effectively modulates hormone release in islets from type 2 diabetic and normoglycaemic individuals.

Show MeSH

Related in: MedlinePlus

Interstitial GABA activates single-channel currents in intact islets. Single-channel currents that were later inhibited by 100 μmol/l SR95531 were recorded in three different cells (a, b, c) from normoglycaemic donors. a A representative current trace (top trace, slow time scale, s) showing GABA-activated single-channel currents and inhibition by 100 μmol/l SR95531. The solid line shows the time when the extracellular solution containing SR95531 was perfused through the recording chamber. The broken lines indicate from where in the recording the current trace on the faster time scale (ms) was obtained. The glucose concentration was 20 mmol/l and the holding potential was −90 mV (a), −70 mV (b) and −70 mV (c). The most prominent single-channel conductance in the cells in a, b and c was 51 pS, 36 pS and 71 pS, respectively. For all three cells, the currents were recorded in the whole-cell patch-clamp configuration from cells in intact islets and were activated by interstitial GABA and inhibited by application of SR95531 (100 μmol/l)
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3369140&req=5

Fig4: Interstitial GABA activates single-channel currents in intact islets. Single-channel currents that were later inhibited by 100 μmol/l SR95531 were recorded in three different cells (a, b, c) from normoglycaemic donors. a A representative current trace (top trace, slow time scale, s) showing GABA-activated single-channel currents and inhibition by 100 μmol/l SR95531. The solid line shows the time when the extracellular solution containing SR95531 was perfused through the recording chamber. The broken lines indicate from where in the recording the current trace on the faster time scale (ms) was obtained. The glucose concentration was 20 mmol/l and the holding potential was −90 mV (a), −70 mV (b) and −70 mV (c). The most prominent single-channel conductance in the cells in a, b and c was 51 pS, 36 pS and 71 pS, respectively. For all three cells, the currents were recorded in the whole-cell patch-clamp configuration from cells in intact islets and were activated by interstitial GABA and inhibited by application of SR95531 (100 μmol/l)

Mentions: The exact interstitial GABA concentration in the islets is not known, but can be assumed to be in the submicromolar range or similar to that in the extracellular fluid in the brain [25]. The highest GABA concentration is expected to be around the beta cell release sites. Using the patch-clamp technique and recording from cells in intact islets, we examined currents from GABAA channels activated by the interstitial GABA originating within the islets, as no GABA was added experimentally. Figure 3a shows whole-cell currents, which were inhibited by the GABAA channel competitive antagonist, SR95531 (100 μmol/l). The upward shift in the baseline current when SR95531 was applied shows the level of the GABA-activated GABAA current. The levels of lines 1 and 2 in Fig. 3a correspond to the peak values (Fig. 3b) of Gaussian fits to histograms of 30 s current records from before and after SR95531 application. The difference between the peak values was 4.4 pA and is the level of the GABA-generated current in the cell. This type of current is termed ‘tonic’, as it is long lasting and can significantly affect cell excitability [20]. In two cells, synaptic-like transient currents were recorded (data not shown) similar to that reported by Braun et al [1, 8]. We examined whether larger tonic currents were generated if we applied no glucose to the cells, but applied 10 mmol/l glutamine. Under these conditions, no tonic currents were recorded (n = 5), but when we applied 20 mmol/l glucose to islets from the same donor, tonic currents were evoked (n = 3). We then examined whether a positive modulator of GABAA channels, pentobarbital, enhanced the GABA-generated tonic currents (Fig. 3c, d). The level of line 3 (Fig. 3c) corresponds to the peak value (Fig. 3d) of the Gaussian fit to a histogram of 30 s current record after 100 μmol/l pentobarbital application to the islet. The level of the GABA-generated tonic current in the cell was 3.6 pA and was enhanced to 7.1 pA by 100 μmol/l pentobarbital (Fig. 3d). Interestingly, GABA-generated tonic currents were minimal or not detected in islets from type 2 diabetic donors until we applied pentobarbital (n = 5, Fig. 3e, f). The results are consistent with pentobarbital enhancing GABAA currents by increasing both the open probability and the channel conductance of GABAA channels, resulting in higher apparent affinity of the channels for GABA. The enhanced current was inhibited by SR95531 (Fig. 3e, f). We recorded single-channel currents from three different cells (Fig. 4a, b, c) in islets from normoglycaemic donors (Fig. 4a, slow time scale (s); Fig. 4a expanded, Fig. 4b and Fig. 4c, fast time scale (ms); the glucose concentration was 20 mmol/l and the holding potential: Fig. 4a, −90 mV; Fig. 4b, −70 mV; Fig. 4c, −70 mV). In all three cells, when the islets were perfused with 100 μmol/l SR95531, the single-channel currents were inhibited. Figure 4a (top current trace, time scale s) shows SR95531 inhibition of the channels in one of the cells. The most prominent single-channel current amplitude recorded in each cell is indicated in Fig. 4 by the dotted lines and gave channel conductance of 51 pS, 36 pS and 71 pS for the cells in Fig. 4a, b and c, respectively.Fig. 3


γ-Aminobutyric acid (GABA) signalling in human pancreatic islets is altered in type 2 diabetes.

Taneera J, Jin Z, Jin Y, Muhammed SJ, Zhang E, Lang S, Salehi A, Korsgren O, Renström E, Groop L, Birnir B - Diabetologia (2012)

Interstitial GABA activates single-channel currents in intact islets. Single-channel currents that were later inhibited by 100 μmol/l SR95531 were recorded in three different cells (a, b, c) from normoglycaemic donors. a A representative current trace (top trace, slow time scale, s) showing GABA-activated single-channel currents and inhibition by 100 μmol/l SR95531. The solid line shows the time when the extracellular solution containing SR95531 was perfused through the recording chamber. The broken lines indicate from where in the recording the current trace on the faster time scale (ms) was obtained. The glucose concentration was 20 mmol/l and the holding potential was −90 mV (a), −70 mV (b) and −70 mV (c). The most prominent single-channel conductance in the cells in a, b and c was 51 pS, 36 pS and 71 pS, respectively. For all three cells, the currents were recorded in the whole-cell patch-clamp configuration from cells in intact islets and were activated by interstitial GABA and inhibited by application of SR95531 (100 μmol/l)
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3369140&req=5

Fig4: Interstitial GABA activates single-channel currents in intact islets. Single-channel currents that were later inhibited by 100 μmol/l SR95531 were recorded in three different cells (a, b, c) from normoglycaemic donors. a A representative current trace (top trace, slow time scale, s) showing GABA-activated single-channel currents and inhibition by 100 μmol/l SR95531. The solid line shows the time when the extracellular solution containing SR95531 was perfused through the recording chamber. The broken lines indicate from where in the recording the current trace on the faster time scale (ms) was obtained. The glucose concentration was 20 mmol/l and the holding potential was −90 mV (a), −70 mV (b) and −70 mV (c). The most prominent single-channel conductance in the cells in a, b and c was 51 pS, 36 pS and 71 pS, respectively. For all three cells, the currents were recorded in the whole-cell patch-clamp configuration from cells in intact islets and were activated by interstitial GABA and inhibited by application of SR95531 (100 μmol/l)
Mentions: The exact interstitial GABA concentration in the islets is not known, but can be assumed to be in the submicromolar range or similar to that in the extracellular fluid in the brain [25]. The highest GABA concentration is expected to be around the beta cell release sites. Using the patch-clamp technique and recording from cells in intact islets, we examined currents from GABAA channels activated by the interstitial GABA originating within the islets, as no GABA was added experimentally. Figure 3a shows whole-cell currents, which were inhibited by the GABAA channel competitive antagonist, SR95531 (100 μmol/l). The upward shift in the baseline current when SR95531 was applied shows the level of the GABA-activated GABAA current. The levels of lines 1 and 2 in Fig. 3a correspond to the peak values (Fig. 3b) of Gaussian fits to histograms of 30 s current records from before and after SR95531 application. The difference between the peak values was 4.4 pA and is the level of the GABA-generated current in the cell. This type of current is termed ‘tonic’, as it is long lasting and can significantly affect cell excitability [20]. In two cells, synaptic-like transient currents were recorded (data not shown) similar to that reported by Braun et al [1, 8]. We examined whether larger tonic currents were generated if we applied no glucose to the cells, but applied 10 mmol/l glutamine. Under these conditions, no tonic currents were recorded (n = 5), but when we applied 20 mmol/l glucose to islets from the same donor, tonic currents were evoked (n = 3). We then examined whether a positive modulator of GABAA channels, pentobarbital, enhanced the GABA-generated tonic currents (Fig. 3c, d). The level of line 3 (Fig. 3c) corresponds to the peak value (Fig. 3d) of the Gaussian fit to a histogram of 30 s current record after 100 μmol/l pentobarbital application to the islet. The level of the GABA-generated tonic current in the cell was 3.6 pA and was enhanced to 7.1 pA by 100 μmol/l pentobarbital (Fig. 3d). Interestingly, GABA-generated tonic currents were minimal or not detected in islets from type 2 diabetic donors until we applied pentobarbital (n = 5, Fig. 3e, f). The results are consistent with pentobarbital enhancing GABAA currents by increasing both the open probability and the channel conductance of GABAA channels, resulting in higher apparent affinity of the channels for GABA. The enhanced current was inhibited by SR95531 (Fig. 3e, f). We recorded single-channel currents from three different cells (Fig. 4a, b, c) in islets from normoglycaemic donors (Fig. 4a, slow time scale (s); Fig. 4a expanded, Fig. 4b and Fig. 4c, fast time scale (ms); the glucose concentration was 20 mmol/l and the holding potential: Fig. 4a, −90 mV; Fig. 4b, −70 mV; Fig. 4c, −70 mV). In all three cells, when the islets were perfused with 100 μmol/l SR95531, the single-channel currents were inhibited. Figure 4a (top current trace, time scale s) shows SR95531 inhibition of the channels in one of the cells. The most prominent single-channel current amplitude recorded in each cell is indicated in Fig. 4 by the dotted lines and gave channel conductance of 51 pS, 36 pS and 71 pS for the cells in Fig. 4a, b and c, respectively.Fig. 3

Bottom Line: The currents were enhanced by pentobarbital and inhibited by the GABA(A) receptor antagonist, SR95531.The effects of SR95531 on hormone release revealed that activation of GABA(A) channels (GABA(A) receptors) decreased both insulin and glucagon secretion.Interstitial GABA activates GABA(A) channels and GABA(B) receptors and effectively modulates hormone release in islets from type 2 diabetic and normoglycaemic individuals.

View Article: PubMed Central - PubMed

Affiliation: Department of Clinical Sciences, Lund University Diabetes Center, University Hospital Malmö, Lund University, Malmö, Sweden.

ABSTRACT

Aims/hypothesis: γ-Aminobutyric acid (GABA) is a signalling molecule in the interstitial space in pancreatic islets. We examined the expression and function of the GABA signalling system components in human pancreatic islets from normoglycaemic and type 2 diabetic individuals.

Methods: Expression of GABA signalling system components was studied by microarray, quantitative PCR analysis, immunohistochemistry and patch-clamp experiments on cells in intact islets. Hormone release was measured from intact islets.

Results: The GABA signalling system was compromised in islets from type 2 diabetic individuals, where the expression of the genes encoding the α1, α2, β2 and β3 GABA(A) channel subunits was downregulated. GABA originating within the islets evoked tonic currents in the cells. The currents were enhanced by pentobarbital and inhibited by the GABA(A) receptor antagonist, SR95531. The effects of SR95531 on hormone release revealed that activation of GABA(A) channels (GABA(A) receptors) decreased both insulin and glucagon secretion. The GABA(B) receptor antagonist, CPG55845, increased insulin release in islets (16.7 mmol/l glucose) from normoglycaemic and type 2 diabetic individuals.

Conclusions/interpretation: Interstitial GABA activates GABA(A) channels and GABA(B) receptors and effectively modulates hormone release in islets from type 2 diabetic and normoglycaemic individuals.

Show MeSH
Related in: MedlinePlus