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Alpha-cobratoxin inhibits T-type calcium currents through muscarinic M4 receptor and Go-protein beta gamma subunits-dependent protein kinase A pathway in dorsal root ganglion neurons

The long-chain neurotoxic protein, alpha-cobratoxin ( alpha -CTx), has been shown to have analgesic effects. However, the underlying mechanisms still remain unclear. In this study, we examined the effects of alpha -CTx on T-type calcium channel currents (T-currents) and elucidated the relevant mecha...

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Bibliographic Details
Published in:Neuropharmacology 2012-02, Vol.62 (2), p.1062-1072
Main Authors: Zhang, Ling, Zhang, Yiming, Jiang, Dongsheng, Reid, Paul F, Jiang, Xinghong, Qin, Zhenghong, Tao, Jin
Format: Article
Language:English
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Summary:The long-chain neurotoxic protein, alpha-cobratoxin ( alpha -CTx), has been shown to have analgesic effects. However, the underlying mechanisms still remain unclear. In this study, we examined the effects of alpha -CTx on T-type calcium channel currents (T-currents) and elucidated the relevant mechanisms in mouse dorsal root ganglion (DRG) neurons. Our results showed that alpha -CTx reversibly inhibited T-currents in a dose-dependent manner. This inhibitory effect was blocked by the selective muscarinic M4 receptor antagonist tropicamide, while methyllycaconitine, a specific antagonist for the alpha 7 subtype of nicotinic receptor had no effect. siRNA targeting the M4 receptor in small DRG neurons abolished alpha -CTx-induced T-current inhibition. Intracellular application of GDP- beta -S or a selective antibody against the G sub(o) alpha -protein, as well as pretreatment of the cells with pertussis toxin, abolished the inhibitory effects of alpha -CTx. The M4 receptor-mediated response was blocked by dialyzing cells with QEHA peptide or anti-G beta antibody. Pretreatment of the cells with protein kinase A (PKA) inhibitor H89 or intracellular application of PKI 6-22 abolished alpha -CTx-induced T-current inhibition in small DRG neurons, whereas inhibition of phosphatidylinositol 3-kinase or PKC elicited no such effects. In addition, alpha -CTx significantly increased PKA activity in DRG neurons, whereas pretreatment of the cells with tropicamide abolished this effect. In summary, our results suggest that activation of muscarinic M4 receptor by alpha -CTx inhibits T-currents via the G beta gamma of G sub(o)-protein and PKA-dependent pathway. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.
ISSN:0028-3908
DOI:10.1016/j.neuropharm.2011.10.017