Høy Marianne, Maechler Pierre, Efanov Alexander M, Wollheim Claes B, Berggren Per Olof, Gromada Jesper
Islet Discovery Research, Novo Nordisk A/S, Novo Alle, Bagsvaerd, Denmark.
FEBS Lett. 2002 Nov 6;531(2):199-203. doi: 10.1016/s0014-5793(02)03500-7.
Glutamate has been implicated as an intracellular messenger in the regulation of insulin secretion in response to glucose. Here we demonstrate by measurements of cell capacitance in rat pancreatic beta-cells that glutamate (1 mM) enhanced Ca2+-dependent exocytosis. Glutamate (1 mM) also stimulated insulin secretion from permeabilized rat beta-cells. The effect was dose-dependent (half-maximum at 5.1 mM) and maximal at 10 mM glutamate. Glutamate-induced exocytosis was stronger in rat beta-cells and clonal INS-1E cells compared to beta-cells isolated from mice and in parental INS-1 cells, which correlated with the expressed levels of glutamate dehydrogenase. Glutamate-induced exocytosis was inhibited by the protonophores FCCP and SF6847, by the vacuolar-type H+-ATPase inhibitor bafilomycin A(1) and by the glutamate transport inhibitor Evans Blue. Our data provide evidence that exocytosis in beta-cells can be modulated by physiological increases in cellular glutamate levels. The results suggest that stimulation of exocytosis is associated with accumulation of glutamate in the secretory granules, a process that is dependent on the transgranular proton gradient.
谷氨酸已被认为是细胞内信使，参与调节葡萄糖刺激的胰岛素分泌。在此，我们通过测量大鼠胰腺β细胞的细胞电容证明，谷氨酸（1 mM）可增强钙离子依赖性胞吐作用。谷氨酸（1 mM）还可刺激通透化大鼠β细胞分泌胰岛素。该效应呈剂量依赖性（在5.1 mM时达到半数最大效应），在10 mM谷氨酸时达到最大效应。与从小鼠分离的β细胞及亲本INS-1细胞相比，谷氨酸诱导的胞吐作用在大鼠β细胞和克隆的INS-1E细胞中更强，这与谷氨酸脱氢酶的表达水平相关。质子载体FCCP和SF6847、液泡型H⁺-ATP酶抑制剂巴弗洛霉素A1以及谷氨酸转运抑制剂伊文思蓝均可抑制谷氨酸诱导的胞吐作用。我们的数据表明，β细胞中的胞吐作用可被细胞内谷氨酸水平的生理性升高所调节。结果提示，胞吐作用的刺激与谷氨酸在分泌颗粒中的积累有关，这一过程依赖于颗粒内质子梯度。
