Activation of M3 muscarinic receptors inhibits T-type Ca(2+) channel currents via pertussis toxin-sensitive novel protein kinase C pathway in small dorsal root ganglion neurons |
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Authors: | Zhang Yiming Zhang Ling Wang Fen Zhang Yi Wang Jiangong Qin Zhenghong Jiang Xinghong Tao Jin |
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Institution: | a Key Laboratory of Pain Research & Therapy, Department of Neurobiology and Medical Psychology, Medical College of Soochow University, Suzhou 215123, Chinab Laboratory of Aging and Nervous Diseases, Department of Pharmacology, Medical College of Soochow University, Suzhou 215123, Chinac Institute of Neuroscience, Soochow University, Suzhou 215123, China |
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Abstract: | Cobrotoxin (CbT), a short-chain postsynaptic α-neurotoxin, has been reported to play a role in analgesia. However, to date, the detailed mechanisms still remain unknown. In the present study, we identify a novel functional role of CbT in modulating T-type Ca2+ channel currents (T-currents) in small dorsal root ganglia (DRG) neurons as well as pain behaviors in mice. We found that CbT inhibited T-currents in a dose-dependent manner. CbT at 1 μM reversibly inhibited T-currents by ~ 26.3%. This inhibitory effect was abolished by the non-selective muscarinic acetylcholine receptor (mAChR) antagonist atropine, or the selective M3 mAChR antagonist 4-DAMP, while naloxone, an opioid receptor antagonist had no effect. Intracellular infusion of GDP-β-S or pretreatment of the cells with pertussis toxin (PTX) completely blocked the inhibitory effects of CbT. Using depolarizing prepulse, we found the absence of direct binding between G-protein βγ subunits and T-type Ca2+ channels in CbT-induced T-current inhibition. CbT responses were abolished by the phospholipase C inhibitor U73122 (but not the inactive analog U73343). The classical and novel protein kinase C (nPKC) antagonist chelerythrine chlorid or GF109203X abolished CbT responses, whereas the classical PKC antagonist Ro31-8820 or inhibition of PKA elicited no such effects. Intrathecal administration of CbT (5 μg/kg) produced antinociceptive effects in mechanical, thermal, and inflammatory pain models. Moreover, CbT-induced antinociception could be abrogated by 4-DAMP. Taken together, these results suggest that CbT acting through M3 mAChR inhibits T-currents via a PTX-sensitive nPKC pathway in small DRG neurons, which could contribute to its analgesic effects in mice. |
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Keywords: | Cobrotoxin (CbT) T-type Ca2+ channel Dorsal root ganglia Whole-cell patch clamp |
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