Huang Dongyang, Huang Sha, Peers Chris, Du Xiaona, Zhang Hailin, Gamper Nikita
Department of Pharmacology, Hebei Medical University, Shijiazhuang, 050011, PR China.
Faculty of Medicine and Health, University of Leeds, Leeds, UK.
Biochem Biophys Res Commun. 2015 Sep 18;465(2):188-93. doi: 10.1016/j.bbrc.2015.07.137. Epub 2015 Jul 31.
Growing evidence suggests that mammalian peripheral somatosensory neurons express functional receptors for gamma-aminobutyric acid, GABAA and GABAB. Moreover, local release of GABA by pain-sensing (nociceptive) nerve fibres has also been suggested. Yet, the functional significance of GABA receptor triggering in nociceptive neurons is not fully understood. Here we used patch-clamp recordings from small-diameter cultured DRG neurons to investigate effects of GABAB receptor agonist baclofen on voltage-gated Ca(2+) currents. We found that baclofen inhibited both low-voltage activated (LVA, T-type) and high-voltage activated (HVA) Ca(2+) currents in a proportion of DRG neurons by 22% and 32% respectively; both effects were sensitive to Gi/o inhibitor pertussis toxin. Inhibitory effect of baclofen on both current types was about twice less efficacious as compared to that of the μ-opioid receptor agonist DAMGO. Surprisingly, only HVA but not LVA current modulation by baclofen was partially prevented by G protein inhibitor GDP-β-S. In contrast, only LVA but not HVA current modulation was reversed by the application of a reducing agent dithiothreitol (DTT). Inhibition of T-type Ca(2+) current by baclofen and the recovery of such inhibition by DTT were successfully reconstituted in the expression system. Our data suggest that inhibition of LVA current in DRG neurons by baclofen is partially mediated by an unconventional signaling pathway that involves a redox mechanism. These findings reinforce the idea of targeting peripheral GABA receptors for pain relief.
越来越多的证据表明，哺乳动物外周躯体感觉神经元表达γ-氨基丁酸（GABA）、GABAA和GABAB的功能性受体。此外，也有人提出痛觉（伤害性）神经纤维会局部释放GABA。然而，GABA受体在伤害性神经元中触发的功能意义尚未完全明确。在这里，我们使用膜片钳记录法，从小直径培养的背根神经节（DRG）神经元中研究GABAB受体激动剂巴氯芬对电压门控Ca(2+)电流的影响。我们发现，巴氯芬在一定比例的DRG神经元中分别抑制低电压激活（LVA，T型）和高电压激活（HVA）Ca(2+)电流22%和32%；这两种效应均对Gi/o抑制剂百日咳毒素敏感。与μ-阿片受体激动剂DAMGO相比，巴氯芬对两种电流类型的抑制作用效力约低两倍。令人惊讶的是，G蛋白抑制剂GDP-β-S仅部分阻止了巴氯芬对HVA电流而非LVA电流的调制。相反，还原剂二硫苏糖醇（DTT）的应用仅逆转了LVA电流而非HVA电流的调制。巴氯芬对T型Ca(2+)电流的抑制作用以及DTT对这种抑制作用的恢复在表达系统中成功重建。我们的数据表明，巴氯芬对DRG神经元中LVA电流的抑制作用部分是由一种涉及氧化还原机制的非常规信号通路介导的。这些发现强化了靶向外周GABA受体以缓解疼痛的观点。
