Impaired inhibitory G-protein function contributes to increased calcium currents in rats with diabetic neuropathy
Impaired inhibitory G-protein function contributes to increased calcium currents in rats with diabetic neuropathy
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DOI：
10.1152/jn.2001.86.2.760
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发表时间：
2001-08-01
影响因子：
2.5
通讯作者：
Wiley, JW
中科院分区：
文献类型：
--
作者：
Hall, KE;Liu, J;Wiley, JW
越来越多的证据表明，糖尿病中的感觉神经病变与背根神经节 (DRG) 神经元中的钙信号异常有关。通过多个高阈值钙电流增强钙的流入存在于几种糖尿病模型的感觉神经元中，包括自发性糖尿病 BioBred/Worchester (BB/W) 大鼠和化学链脲佐菌素 (STZ) 诱导的大鼠。我们认为，糖尿病中异常的钙信号传导具有病理意义，因为钙流入和胞质钙释放的增加与其他以神经元功能障碍和死亡为特征的神经退行性疾病有关。利用电生理学和药理学技术，本研究提供的证据表明，钙通道功能的 G 蛋白偶联调节的显着损害可能是糖尿病中钙进入增强的基础。 DRG 中的 N 型和 P 型电压激活高阈值钙通道通过抑制性 G(o) 型 G 蛋白与 mu 阿片受体偶联。该受体偶联模型的反应性在自发性糖尿病 BB/W 大鼠和链脲佐菌素诱导的 (STZ) 糖尿病大鼠的背根神经节 (DRG) 神经元中进行了测试。与年龄匹配的非糖尿病对照相比，GTP gammaS 细胞内透析降低了糖尿病 BB/W DRG 神经元的钙电流幅度，表明糖尿病中抑制性 G 蛋白活性减弱，导致钙电流增大。大振幅去极化预脉冲（建议暂时失活 G 蛋白）促进钙电流密度 (I-DCa) 对于 BB/W 和 STZ 诱导的糖尿病 DRG 的神经元的效果明显较差。 GTP gammaS 细胞内透析可增强促进作用，百日咳毒素可降低促进作用，GDP betaS 可在 5 分钟内消除促进作用。使用阿片介导的 GTP gamma[S-35] 结合直接测量 GTPase 活性，证实与年龄匹配的非糖尿病对照相比，STZ 诱导的糖尿病神经元中的 G 蛋白活性显着降低。糖尿病不会改变μ阿片受体和G蛋白α亚基的表达水平。这些研究表明，G 蛋白对钙通道的调节受损是导致糖尿病钙流入增加的重要机制。
There is a growing body of evidence that sensory neuropathy in diabetes is associated with abnormal calcium signaling in dorsal root ganglion (DRG) neurons. Enhanced influx of calcium via multiple high-threshold calcium currents is present in sensory neurons of several models of diabetes mellitus, including the spontaneously diabetic BioBred/Worchester (BB/W) rat and the chemical streptozotocin (STZ)-induced rat. We believe that abnormal calcium signaling in diabetes has pathologic significance as elevation of calcium influx and cytosolic calcium release has been implicated in other neurodegenerative conditions characterized by neuronal dysfunction and death. Using electrophysiologic and pharmacologic techniques, the present study provides evidence that significant impairment of G-protein-coupled modulation of calcium channel function may underlie the enhanced calcium entry in diabetes. N- and P-type voltage-activated, high-threshold calcium channels in DRGs are coupled to mu opiate receptors via inhibitory G(o)-type G proteins. The responsiveness of this receptor coupled model was tested in dorsal root ganglion (DRG) neurons from spontaneously-diabetic BB/W rats, and streptozotocin-induced (STZ) diabetic rats. Intracellular dialysis with GTP gammaS decreased calcium current amplitude in diabetic BB/W DRG neurons compared with those of age-matched, nondiabetic controls, suggesting that inhibitory G-protein activity was diminished in diabetes, resulting in larger calcium currents. Facilitation of calcium current density (I-DCa) by large-amplitude depolarizing prepulses (proposed to transiently inactivate G proteins), was significantly less effective in neurons from BB/W and STZ-induced diabetic DRGs. Facilitation was enhanced by intracellular dialysis with GTP gammaS, decreased by pertussis toxin, and abolished by GDP betaS within 5 min. Direct measurement of GTPase activity using opiate-mediated GTP gamma[S-35] binding, confirmed that G-protein activity was significantly diminished in STZ-induced diabetic neurons compared with age-matched nondiabetic controls. Diabetes did not alter the level of expression of mu opiate receptors and G-protein alpha subunits. These studies indicate that impaired regulation of calcium channels by G proteins is an important mechanism contributing to enhanced calcium influx in diabetes.