ABSTRACT
Neuropathic pain is a chronic debilitating symptom characterized by spontaneous pain and mechanical allodynia. It occurs in distinct forms, including brush-evoked dynamic and filament-evoked punctate mechanical allodynia. Potassium channel 2.1 (Kir2.1), which exhibits strong inward rectification, is and regulates the activity of lamina I projection neurons. However, the relationship between Kir2.1 channels and mechanical allodynia is still unclear. In this study, we first found that pretreatment with ML133, a selective Kir2.1 inhibitor, by intrathecal administration, preferentially inhibited dynamic, but not punctate, allodynia in mice with spared nerve injury (SNI). Intrathecal injection of low doses of strychnine, a glycine receptor inhibitor, selectively induced dynamic, but not punctate allodynia, not only in naïve but also in ML133-pretreated mice. In contrast, bicuculline, a GABA receptor antagonist, induced only punctate, but not dynamic, allodynia. These results indicated the involvement of glycinergic transmission in the development of dynamic allodynia. We further found that SNI significantly suppressed the frequency, but not the amplitude, of the glycinergic spontaneous inhibitory postsynaptic currents (gly-sIPSCs) in neurons on the lamina II-III border of the spinal dorsal horn, and pretreatment with ML133 prevented the SNI-induced gly-sIPSC reduction. Furthermore, 5 days after SNI, ML133, either by intrathecal administration or acute bath perfusion, and strychnine sensitively reversed the SNI-induced dynamic, but not punctate, allodynia and the gly-sIPSC reduction in lamina IIi neurons, respectively. In conclusion, our results suggest that blockade of Kir2.1 channels in the spinal dorsal horn selectively inhibits dynamic, but not punctate, mechanical allodynia by enhancing glycinergic inhibitory transmission.
Subject(s)
Animals , Male , Bicuculline , Pharmacology , Disease Models, Animal , Glycine , Metabolism , Hyperalgesia , Drug Therapy , Metabolism , Imidazoles , Pharmacology , Inhibitory Postsynaptic Potentials , Physiology , Mice, Inbred C57BL , Neurons , Metabolism , Neurotransmitter Agents , Pharmacology , Peripheral Nerve Injuries , Drug Therapy , Metabolism , Phenanthrolines , Pharmacology , Potassium Channels, Inwardly Rectifying , Metabolism , Receptors, GABA-A , Metabolism , Receptors, Glycine , Metabolism , Strychnine , Pharmacology , Synaptic Transmission , Physiology , Tissue Culture Techniques , TouchABSTRACT
ObjectiveTo test what length is needed for polyamine binding both intrinsic gate and pore docking site to block the cloned strong inwardly rectifying channel (Kir2. 1 channel). Methods The effect of alkylamine analogues (DA 5, DA 8, DA 10 and DA 12) and the competitive interaction of polyamine toxin, philanthotoxin (PhTx), on expressed Kir 2. 1channel in Xenopus oocytes were examined by using giant excised inside-out patch-clamp technique. ResultsThe results showed that along with the increase of the length of DAs ,the value of Kd decreased and the high affinity binding increased gradually. However,PhTx had the strongest effect on interfering the DA10 binding between intrinsic gate and pore docking site and had a less effect on DA12. Conclusion DA10 may be the right length for polyamine to block the channel. And maybe there is a hydrophobic interaction between DA12 and C-terminal domain of this channel, which then stabilize the DA12 binding between these two points and decrease the effect of PhTx on DA12.