Gamma-aminobutyric acid (GABA) is an autocrine excitatory transmitter in human pancreatic beta-cells.
Gamma-aminobutyric acid (GABA) is an autocrine excitatory transmitter in human pancreatic beta-cells.
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作者：
Braun M;Ramracheya R;Bengtsson M;Clark A;Walker JN;Johnson PR;Rorsman P
在啮齿类动物的胰岛中，已发现通过γ-氨基丁酸和GABA受体(GABA受体)传递旁分泌信号。在这里，我们研究了GABA能信号在人胰岛中的重要性。用定量聚合酶链式反应、免疫组织化学和膜片钳实验研究GABAARs在胰岛细胞中的表达。测量完整胰岛的激素释放。腺病毒表达α-1、β-1GABAAR亚基后，采用全细胞膜片钳技术监测GABAAR的释放。用电子显微镜观察GABA的亚细胞定位。穿孔膜片全细胞记录法测定GABA对电活动的影响。聚合酶链式反应分析在人胰岛中检测到较高水平的编码α2、β3、γ2和π亚单位的mRNAs。膜片钳实验显示−通道在52%的β-细胞(电流密度为9pA/pF)、91%的δ-细胞(电流密度为148pA/pF)和6%的α-细胞(电流密度为2 pA/pF)中表达。免疫组织化学方法证实胰岛细胞表达GABAAR亚基。β细胞通过含胰岛素颗粒的葡萄糖依赖性胞吐和葡萄糖非依赖性机制分泌γ-氨基丁酸。GABA受体拮抗剂SR95531可抑制6 mmol/L葡萄糖诱导的胰岛素分泌。应用γ-氨基丁酸使β细胞去极化，并刺激葡萄糖作用下β细胞的动作电位放电。在人β细胞中，通过γ-氨基丁酸和γ-氨基丁酸受体的信号传递构成了一个自分泌正反馈环。在非β细胞中GABA的存在提示GABA可能也参与了生长抑素和胰升糖素的分泌调节。
Paracrine signaling via γ-aminobutyric acid (GABA) and GABAA receptors (GABAARs) has been documented in rodent islets. Here we have studied the importance of GABAergic signaling in human pancreatic islets. Expression of GABAARs in islet cells was investigated by quantitative PCR, immunohistochemistry, and patch-clamp experiments. Hormone release was measured from intact islets. GABA release was monitored by whole-cell patch-clamp measurements after adenoviral expression of α1β1 GABAAR subunits. The subcellular localization of GABA was explored by electron microscopy. The effects of GABA on electrical activity were determined by perforated patch whole-cell recordings. PCR analysis detected relatively high levels of the mRNAs encoding GABAAR α2, β3, γ2, and π subunits in human islets. Patch-clamp experiments revealed expression of GABAAR Cl− channels in 52% of β-cells (current density 9 pA/pF), 91% of δ-cells (current density 148 pA/pF), and 6% of α-cells (current density 2 pA/pF). Expression of GABAAR subunits in islet cells was confirmed by immunohistochemistry. β-Cells secreted GABA both by glucose-dependent exocytosis of insulin-containing granules and by a glucose-independent mechanism. The GABAAR antagonist SR95531 inhibited insulin secretion elicited by 6 mmol/l glucose. Application of GABA depolarized β-cells and stimulated action potential firing in β-cells exposed to glucose. Signaling via GABA and GABAAR constitutes an autocrine positive feedback loop in human β-cells. The presence of GABAAR in non–β-cells suggests that GABA may also be involved in the regulation of somatostatin and glucagon secretion.