Weaver C D, Partridge J G, Yao T L, Moates J M, Magnuson M A, Verdoorn T A
Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-6600, USA.
Mol Pharmacol. 1998 Oct;54(4):639-46.
We studied calcium signaling in a newly described pancreatic cell line, GK-P3, that expresses functional amino acid neurotransmitter receptors. GK-P3 cells express the first strychnine-sensitive glycine receptors reported in a permanent cell line. In addition, GK-P3 cells express alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors. Both types of amino acid receptors showed electrophysiological and pharmacological behavior similar to their neuronal counterparts. The glycine receptors were permeable to Cl- and blocked by the selective antagonist strychnine. AMPA receptors showed limited permeability to Ca2+, were blocked by 6-cyano-2, 3-dihydroxy-7-nitroquinoxaline, and were potentiated by cyclothiazide. Interestingly, activation of either receptor type increased intracellular Ca2+ measured by digital imaging of Fura-2 fluorescence. These Ca2+ signals were completely blocked by 30 microM La3+, suggesting that the Ca2+ entered the cells largely through voltage-dependent Ca2+ channels. Alterations in the extracellular concentrations of Cl- and/or HCO3- had only marginal effects on glycine-evoked Ca2+ signals. However, increases in intracellular Ca2+ mediated by AMPA receptors were absent when the extracellular Na+ was replaced with an impermeant cation, N-methyl-D-glucamine. We conclude that activation of ligand-gated cation or anion channels depolarize GK-P3 cells sufficiently to activate their voltage-gated Ca2+ channels leading to increases in intracellular Ca2+ concentration. Thus, glycine and glutamate receptors may regulate Ca2+-dependent secretory mechanisms in islet cells by altering the membrane potential of these cells. Our data in GK-P3 cells support the growing weight of evidence for a role of amino acid neurotransmitters in pancreatic islets and introduce strychnine-sensitive glycine receptors as a novel target of amino acid neurotransmitter regulation in islets.
我们研究了一种新描述的胰腺细胞系GK-P3中的钙信号传导，该细胞系表达功能性氨基酸神经递质受体。GK-P3细胞表达了在永久细胞系中首次报道的对士的宁敏感的甘氨酸受体。此外，GK-P3细胞表达α-氨基-3-羟基-5-甲基-4-异恶唑丙酸（AMPA）型谷氨酸受体。这两种类型的氨基酸受体均表现出与其神经元对应物相似的电生理和药理行为。甘氨酸受体对Cl-具有通透性，并被选择性拮抗剂士的宁阻断。AMPA受体对Ca2+的通透性有限，被6-氰基-2,3-二羟基-7-硝基喹喔啉阻断，并被环噻嗪增强。有趣的是，通过Fura-2荧光数字成像测量，任何一种受体类型的激活都会增加细胞内Ca2+。这些Ca2+信号被30 microM La3+完全阻断，表明Ca2+主要通过电压依赖性Ca2+通道进入细胞。细胞外Cl-和/或HCO3-浓度的改变对甘氨酸诱发的Ca2+信号仅有轻微影响。然而，当细胞外Na+被不透性阳离子N-甲基-D-葡糖胺替代时，由AMPA受体介导的细胞内Ca2+增加消失。我们得出结论，配体门控阳离子或阴离子通道的激活足以使GK-P3细胞去极化，从而激活其电压门控Ca2+通道，导致细胞内Ca2+浓度增加。因此，甘氨酸和谷氨酸受体可能通过改变这些细胞的膜电位来调节胰岛细胞中依赖Ca2+的分泌机制。我们在GK-P3细胞中的数据支持了越来越多的证据表明氨基酸神经递质在胰岛中起作用，并将对士的宁敏感的甘氨酸受体引入作为胰岛中氨基酸神经递质调节的新靶点。
