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GABA coordinates with insulin in regulating secretory function in pancreatic INS-1 β-cells.

Bansal P, Wang S, Liu S, Xiang YY, Lu WY, Wang Q - PLoS ONE (2011)

Bottom Line: Here we investigate the effects of insulin on the GABA-GABA(A)R system in the pancreatic INS-1 cells using perforated-patch recording.The results showed that GABA produces a rapid inward current and depolarizes INS-1 cells.On the other hand, insulin down-regulates GABA-GABA(A)R signaling presenting a feedback mechanism for fine-tuning β-cell secretion.

View Article: PubMed Central - PubMed

Affiliation: Departments of Physiology and Medicine, University of Toronto, Toronto, Ontario, Canada.

ABSTRACT
Pancreatic islet β-cells produce large amounts of γ-aminobutyric acid (GABA), which is co-released with insulin. GABA inhibits glucagon secretion by hyperpolarizing α-cells via type-A GABA receptors (GABA(A)Rs). We and others recently reported that islet β-cells also express GABA(A)Rs and that activation of GABA(A)Rs increases insulin release. Here we investigate the effects of insulin on the GABA-GABA(A)R system in the pancreatic INS-1 cells using perforated-patch recording. The results showed that GABA produces a rapid inward current and depolarizes INS-1 cells. However, pre-treatment of the cell with regular insulin (1 µM) suppressed the GABA-induced current (I(GABA)) by 43%. Zinc-free insulin also suppressed I(GABA) to the same extent of inhibition by regular insulin. The inhibition of I(GABA) occurs within 30 seconds after application of insulin. The insulin-induced inhibition of I(GABA) persisted in the presence of PI3-kinase inhibitor, but was abolished upon inhibition of ERK, indicating that insulin suppresses GABA(A)Rs through a mechanism that involves ERK activation. Radioimmunoassay revealed that the secretion of C-peptide was enhanced by GABA, which was blocked by pre-incubating the cells with picrotoxin (50 µM, p<0.01) and insulin (1 µM, p<0.01), respectively. Together, these data suggest that autocrine GABA, via activation of GABA(A)Rs, depolarizes the pancreatic β-cells and enhances insulin secretion. On the other hand, insulin down-regulates GABA-GABA(A)R signaling presenting a feedback mechanism for fine-tuning β-cell secretion.

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GABA-evoked currents (IGABA) is inhibited by insulin in INS-1 cells.GABA-evoked inward current was measured by means of a computer-controlled multi-barrelled perfusion system, in two-minute intervals, under voltage-clamp conditions. Representative traces of GABA-evoked currents in the absence and presence of insulin (100 nM, (A), 1 µM, (B)) in the same INS-1 cell. A' and B' represents the average of IGABA from separated experiments. (C) Normalized average IGABA during the course of experiment (control = average of first 4 IGABA, insulin = average of IGABA in the presence insulin at indicated concentrations). Data were mean ± SE. *p<0.05 ** p<0.01, n = 6.
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pone-0026225-g002: GABA-evoked currents (IGABA) is inhibited by insulin in INS-1 cells.GABA-evoked inward current was measured by means of a computer-controlled multi-barrelled perfusion system, in two-minute intervals, under voltage-clamp conditions. Representative traces of GABA-evoked currents in the absence and presence of insulin (100 nM, (A), 1 µM, (B)) in the same INS-1 cell. A' and B' represents the average of IGABA from separated experiments. (C) Normalized average IGABA during the course of experiment (control = average of first 4 IGABA, insulin = average of IGABA in the presence insulin at indicated concentrations). Data were mean ± SE. *p<0.05 ** p<0.01, n = 6.

Mentions: Under voltage-clamp mode, perfusion of GABA evoked typical bicuculline-sensitive GABA current (Figure 2A). We next determined the effect of insulin on GABA-induced current (IGABA). Treatment of INS-1 cells with insulin (100 nM) significantly decreased IGABA by 22% (P<0.05, n = 8). The insulin-induced suppression of IGABA was more prominent when the insulin concentration was increased, for instance a reduction of 43% in IGABA was achieved with 1 µM insulin (Figure 2A, 2B p<0.05, n = 5). Thus, insulin-induced suppression of IGABA was dose-dependent (Figure 2C).


GABA coordinates with insulin in regulating secretory function in pancreatic INS-1 β-cells.

Bansal P, Wang S, Liu S, Xiang YY, Lu WY, Wang Q - PLoS ONE (2011)

GABA-evoked currents (IGABA) is inhibited by insulin in INS-1 cells.GABA-evoked inward current was measured by means of a computer-controlled multi-barrelled perfusion system, in two-minute intervals, under voltage-clamp conditions. Representative traces of GABA-evoked currents in the absence and presence of insulin (100 nM, (A), 1 µM, (B)) in the same INS-1 cell. A' and B' represents the average of IGABA from separated experiments. (C) Normalized average IGABA during the course of experiment (control = average of first 4 IGABA, insulin = average of IGABA in the presence insulin at indicated concentrations). Data were mean ± SE. *p<0.05 ** p<0.01, n = 6.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3198728&req=5

pone-0026225-g002: GABA-evoked currents (IGABA) is inhibited by insulin in INS-1 cells.GABA-evoked inward current was measured by means of a computer-controlled multi-barrelled perfusion system, in two-minute intervals, under voltage-clamp conditions. Representative traces of GABA-evoked currents in the absence and presence of insulin (100 nM, (A), 1 µM, (B)) in the same INS-1 cell. A' and B' represents the average of IGABA from separated experiments. (C) Normalized average IGABA during the course of experiment (control = average of first 4 IGABA, insulin = average of IGABA in the presence insulin at indicated concentrations). Data were mean ± SE. *p<0.05 ** p<0.01, n = 6.
Mentions: Under voltage-clamp mode, perfusion of GABA evoked typical bicuculline-sensitive GABA current (Figure 2A). We next determined the effect of insulin on GABA-induced current (IGABA). Treatment of INS-1 cells with insulin (100 nM) significantly decreased IGABA by 22% (P<0.05, n = 8). The insulin-induced suppression of IGABA was more prominent when the insulin concentration was increased, for instance a reduction of 43% in IGABA was achieved with 1 µM insulin (Figure 2A, 2B p<0.05, n = 5). Thus, insulin-induced suppression of IGABA was dose-dependent (Figure 2C).

Bottom Line: Here we investigate the effects of insulin on the GABA-GABA(A)R system in the pancreatic INS-1 cells using perforated-patch recording.The results showed that GABA produces a rapid inward current and depolarizes INS-1 cells.On the other hand, insulin down-regulates GABA-GABA(A)R signaling presenting a feedback mechanism for fine-tuning β-cell secretion.

View Article: PubMed Central - PubMed

Affiliation: Departments of Physiology and Medicine, University of Toronto, Toronto, Ontario, Canada.

ABSTRACT
Pancreatic islet β-cells produce large amounts of γ-aminobutyric acid (GABA), which is co-released with insulin. GABA inhibits glucagon secretion by hyperpolarizing α-cells via type-A GABA receptors (GABA(A)Rs). We and others recently reported that islet β-cells also express GABA(A)Rs and that activation of GABA(A)Rs increases insulin release. Here we investigate the effects of insulin on the GABA-GABA(A)R system in the pancreatic INS-1 cells using perforated-patch recording. The results showed that GABA produces a rapid inward current and depolarizes INS-1 cells. However, pre-treatment of the cell with regular insulin (1 µM) suppressed the GABA-induced current (I(GABA)) by 43%. Zinc-free insulin also suppressed I(GABA) to the same extent of inhibition by regular insulin. The inhibition of I(GABA) occurs within 30 seconds after application of insulin. The insulin-induced inhibition of I(GABA) persisted in the presence of PI3-kinase inhibitor, but was abolished upon inhibition of ERK, indicating that insulin suppresses GABA(A)Rs through a mechanism that involves ERK activation. Radioimmunoassay revealed that the secretion of C-peptide was enhanced by GABA, which was blocked by pre-incubating the cells with picrotoxin (50 µM, p<0.01) and insulin (1 µM, p<0.01), respectively. Together, these data suggest that autocrine GABA, via activation of GABA(A)Rs, depolarizes the pancreatic β-cells and enhances insulin secretion. On the other hand, insulin down-regulates GABA-GABA(A)R signaling presenting a feedback mechanism for fine-tuning β-cell secretion.

Show MeSH
Related in: MedlinePlus