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

Neuropharmacology. 2012 Feb;62(2):1062-72. doi: 10.1016/j.neuropharm.2011.10.017. Epub 2011 Nov 4.


The long-chain neurotoxic protein, alpha-cobratoxin (α-CTx), has been shown to have analgesic effects. However, the underlying mechanisms still remain unclear. In this study, we examined the effects of α-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 α-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 α7 subtype of nicotinic receptor had no effect. siRNA targeting the M4 receptor in small DRG neurons abolished α-CTx-induced T-current inhibition. Intracellular application of GDP-β-S or a selective antibody against the G(o)α-protein, as well as pretreatment of the cells with pertussis toxin, abolished the inhibitory effects of α-CTx. The M4 receptor-mediated response was blocked by dialyzing cells with QEHA peptide or anti-G(β) antibody. Pretreatment of the cells with protein kinase A (PKA) inhibitor H89 or intracellular application of PKI 6-22 abolished α-CTx-induced T-current inhibition in small DRG neurons, whereas inhibition of phosphatidylinositol 3-kinase or PKC elicited no such effects. In addition, α-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 α-CTx inhibits T-currents via the G(βγ) of G(o)-protein and PKA-dependent pathway. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium / metabolism
  • Calcium Channels, T-Type / metabolism*
  • Cells, Cultured
  • Cobra Neurotoxin Proteins / pharmacology*
  • Cyclic AMP-Dependent Protein Kinases / metabolism*
  • Dose-Response Relationship, Drug
  • GTP-Binding Proteins / metabolism*
  • Ganglia, Spinal / cytology
  • Ganglia, Spinal / drug effects
  • Ganglia, Spinal / metabolism*
  • Membrane Potentials / drug effects
  • Membrane Potentials / physiology
  • Mice
  • Neurons / cytology
  • Neurons / drug effects
  • Neurons / metabolism*
  • Receptor, Muscarinic M4 / metabolism*
  • Signal Transduction / physiology


  • Calcium Channels, T-Type
  • Cobra Neurotoxin Proteins
  • Receptor, Muscarinic M4
  • alpha-cobratoxin
  • Cyclic AMP-Dependent Protein Kinases
  • GTP-Binding Proteins
  • Calcium