Department of Anesthesiology and Perioperative Medicine, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030, USA.
J Biol Chem. 2011 Sep 23;286(38):33190-202. doi: 10.1074/jbc.M111.270967. Epub 2011 Aug 3.
Nitric oxide (NO) is involved in many physiological functions, but its role in pain signaling remains uncertain. Surprisingly, little is known about how endogenous NO affects excitatory and inhibitory synaptic transmission at the spinal level. Here we determined how NO affects excitatory and inhibitory synaptic inputs to dorsal horn neurons using whole-cell recordings in rat spinal cord slices. The NO precursor L-arginine or the NO donor SNAP significantly increased the frequency of glycinergic spontaneous and miniature inhibitory postsynaptic currents (IPSCs) of lamina II neurons. However, neither L-arginine nor SNAP had any effect on GABAergic IPSCs. L-arginine and SNAP significantly reduced the amplitude of monosynaptic excitatory postsynaptic currents (EPSCs) evoked from the dorsal root with an increase in paired-pulse ratio. Inhibition of the soluble guanylyl cyclase abolished the effect of L-arginine on glycinergic IPSCs but not on evoked monosynaptic EPSCs. Also, inhibition of protein kinase G blocked the increase in glycinergic sIPSCs by the cGMP analog 8-bromo-cGMP. The inhibitory effects of L-arginine on evoked EPSCs and high voltage-activated Ca(2+) channels expressed in HEK293 cells and dorsal root ganglion neurons were abolished by blocking the S-nitrosylation reaction with N-ethylmaleimide. Intrathecal injection of L-arginine and SNAP significantly increased mechanical nociceptive thresholds. Our findings suggest that spinal endogenous NO enhances inhibitory glycinergic input to dorsal horn neurons through sGC-cGMP-protein kinase G. Furthermore, NO reduces glutamate release from primary afferent terminals through S-nitrosylation of voltage-activated Ca(2+) channels. Both of these actions probably contribute to inhibition of nociceptive transmission by NO at the spinal level.
一氧化氮（NO）参与许多生理功能，但它在疼痛信号传递中的作用尚不确定。令人惊讶的是，对于内源性 NO 如何影响脊髓水平的兴奋性和抑制性突触传递，人们知之甚少。在这里，我们使用大鼠脊髓切片的全细胞膜片钳记录来确定 NO 如何影响背角神经元的兴奋性和抑制性突触输入。NO 前体 L-精氨酸或 NO 供体 SNAP 显著增加了 II 层神经元的甘氨酸能自发性和微小抑制性突触后电流（IPSCs）的频率。然而，L-精氨酸和 SNAP 对 GABA 能 IPSCs 均无影响。L-精氨酸和 SNAP 显著降低了从背根诱发的单突触兴奋性突触后电流（EPSCs）的幅度，并增加了成对脉冲比。可溶性鸟苷酸环化酶的抑制消除了 L-精氨酸对甘氨酸能 IPSCs 的作用，但对诱发的单突触 EPSCs 没有影响。此外，蛋白激酶 G 的抑制阻断了 cGMP 类似物 8-溴-cGMP 对甘氨酸能 sIPSCs 的增加。用 N-乙基马来酰亚胺阻断 S-亚硝基化反应，消除了 L-精氨酸对 HEK293 细胞和背根神经节神经元表达的诱发 EPSCs 和高电压激活 Ca(2+)通道的抑制作用。鞘内注射 L-精氨酸和 SNAP 显著提高了机械性痛觉阈值。我们的研究结果表明，脊髓内源性 NO 通过 sGC-cGMP-蛋白激酶 G 增强背角神经元的抑制性甘氨酸能输入。此外，NO 通过电压激活 Ca(2+)通道的 S-亚硝基化作用减少初级传入末梢的谷氨酸释放。这两种作用可能都有助于 NO 在脊髓水平抑制伤害性传递。
