Chen Chong, Wang Songhua, Hu Qingjuan, Zeng Lvming, Peng Hailong, Liu Chao, Huang Li-Ping, Song Hao, Li Yuping, Yao Li-Hua, Meng Wei
School of Life science, Jiangxi Science & Technology Normal University, Nanchang, China.
Jiangxi Key Laboratory of Organic Chemistry, Jiangxi Science & Technology Normal University, Nanchang, China.
Cell Physiol Biochem. 2018;45(2):446-457. doi: 10.1159/000486921. Epub 2018 Jan 24.
BACKGROUND/AIMS: Islet beta cells (β-cells) are unique cells that play a critical role in glucose homeostasis by secreting insulin in response to increased glucose levels. Voltage-gated ion channels in β-cells, such as K+ and Ca2+ channels, contribute to insulin secretion. The response of voltage-gated Na+ channels (VGSCs) in β-cells to the changes in glucose levels remains unknown. This work aims to determine the role of extracellular glucose on the regulation of VGSC.
The effect of glucose on VGSC currents (INa) was investigated in insulin-secreting β-cell line (INS-1) cells of rats using whole-cell patch clamp techniques, and the effects of glucose on insulin content and cell viability were determined using Enzyme-Linked Immunosorbent Assay (ELISA) and Methylthiazolyldiphenyl-tetrazolium Bromide (MTT) assay methods respectively.
Our results show that extracellular glucose application can inhibit the peak of INa in a concentration-dependent manner. Glucose concentration of 18 mM reduced the amplitude of INa, suppressed the INa of steady-state activation, shifted the steady-state inactivation curves of INa to negative potentials, and prolonged the time course of INa recovery from inactivation. Glucose also enhanced the activity-dependent attenuation of INa and reduced the fraction of activated channels. Furthermore, 18 mM glucose or low concentration of tetrodotoxin (TTX, a VGSC-specific blocker) partially inhibited the activity of VGSC and also improved insulin synthesis.
These results revealed that extracellular glucose application enhances the insulin synthesis in INS-1 cells and the mechanism through the partial inhibition on INa channel is involved. Our results innovatively suggest that VGSC plays a vital role in modulating glucose homeostasis.
背景/目的：胰岛β细胞是独特的细胞，通过在血糖水平升高时分泌胰岛素，在葡萄糖稳态中发挥关键作用。β细胞中的电压门控离子通道，如钾离子通道和钙离子通道，有助于胰岛素分泌。β细胞中电压门控钠离子通道（VGSCs）对葡萄糖水平变化的反应尚不清楚。本研究旨在确定细胞外葡萄糖对VGSC调节的作用。
采用全细胞膜片钳技术研究葡萄糖对大鼠胰岛素分泌β细胞系（INS-1）细胞中VGSC电流（INa）的影响，分别用酶联免疫吸附测定法（ELISA）和甲基噻唑基二苯基溴化四氮唑（MTT）法测定葡萄糖对胰岛素含量和细胞活力的影响。
我们的结果表明，应用细胞外葡萄糖可浓度依赖性地抑制INa峰值。18 mM的葡萄糖浓度降低了INa的幅度，抑制了稳态激活的INa，使INa的稳态失活曲线向负电位移动，并延长了INa从失活状态恢复的时间进程。葡萄糖还增强了INa的活动依赖性衰减，并减少了激活通道的比例。此外，18 mM葡萄糖或低浓度的河豚毒素（TTX，一种VGSC特异性阻滞剂）部分抑制了VGSC的活性，同时也改善了胰岛素合成。
这些结果表明，应用细胞外葡萄糖可增强INS-1细胞中的胰岛素合成，其机制涉及对INa通道的部分抑制。我们的结果创新性地表明，VGSC在调节葡萄糖稳态中起着至关重要的作用。
