title: Modulation of A-type K+ channels by the short-chain cobrotoxin through the protein kinase C-delta isoform decreases membrane excitability in dorsal root ganglion neurons.
abstract: A-type K(+) channels are crucial in controlling neuronal excitability, and their regulation in sensory neurons may alter pain sensation. In this study, we identified the functional role of cobrotoxin, the short-chain α-neurotoxin isolated from Naja atra venom, which acts in the regulation of the transient A-type K(+) currents (IA) and membrane excitability in dorsal root ganglion (DRG) neurons via the activation of the muscarinic M3 receptor (M3R). Our results showed that cobrotoxin increased IA in a concentration-dependent manner, whereas the sustained delayed rectifier K(+) currents (IDR) were not affected. Cobrotoxin did not affect the activation of IA markedly, however, it shifted the inactivation curve significantly in the depolarizing direction. The cobrotoxin-induced IA response was blocked by the M3R-selective antagonists DAU-5884 and 4-DAMP. An siRNA targeting the M3R in small DRG neurons abolished the cobrotoxin-induced IA increase. In addition, dialysis of the cells with the novel protein kinase C-delta isoform (PKC-δ) inhibitor δv1-1 or an siRNA targeting PKC-δ abolished the cobrotoxin-induced IA response, whereas inhibition of PKA or classic PKC activity elicited no such effects. Moreover, we observed a significant decrease in the firing rate of the neuronal action potential induced by M3R activation. Pretreatment of the cells with 4-aminopyridine, a selective blocker of IA, abolished this effect. Taken together, these results suggest that the short-chain cobrotoxin selectively enhances IA via a novel PKC-δ-dependent pathway. This effect occurred via the activation of M3R and might contribute to its neuronal hypoexcitability in small DRG neurons.
authors: Department of Emergency and Intensive Care Unit & Institute of Neuroscience, The First Affiliated Hospital of Soochow University, Suzhou 215006, PR China.
authors: Qiang
authors: Q
authors: Guo
authors: You-Jing
authors: YJ
authors: Jiang
authors: Hong
authors: H
authors: Jin
authors: Xing-Hong
authors: XH
authors: Jiang
authors: Bo
authors: B
authors: Gu
authors: Yi-Ming
authors: YM
authors: Zhang
authors: Jian-Gong
authors: JG
authors: Wang
authors: Zheng-Hong
authors: ZH
authors: Qin
authors: Jin
authors: J
authors: Tao
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology*; D003039:Cobra Neurotoxin Proteins / Q000494:pharmacology*; D005727:Ganglia, Spinal / Q000166:cytology / Q000502:physiology*; D055785:Gene Knockdown Techniques; D066298:In Vitro Techniques; D051605:Kv Channel-Interacting Proteins / Q000502:physiology*; D051379:Mice; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D051745:Protein Kinase C-delta / Q000235:genetics / Q000502:physiology*; D043587:Receptor, Muscarinic M3 / Q000502:physiology
chemical_list: D003039:Cobra Neurotoxin Proteins; D051605:Kv Channel-Interacting Proteins; D043587:Receptor, Muscarinic M3; D051745:Protein Kinase C-delta