Voltage-gated sodium channels Xiao Yu Institute of Physiology Shandong University, School of Medicine 2012-11-10
Sodium channel genes are latecomers to the 6TM Family (Zakon HH, PNAS 2012)
Sodium Channels - Structure • Composed of α, β-1 and β-2 subunits, but the large α-subunits carries most of the functional properties • 4 repeated motifs, each with 6 transmembrane domains • All linked together • Contain a voltage “sensor”/ligand binding domain (method of activation) • The hydrophobic S4 segment (voltage “sensor”) is found in all voltage gated Na+ channels and is absent in ligand gated Na+ channels • Selectivity filter (shell of hydration) • Inactivation gate
Outline • 1. Physiological studies • 2. Pharmacological studies • 3. Biochemical studies • 4. Pathological and further studies
Physiological properties of VGSCs: activation, inactivation, recovery (Neuroscience: Exploring the Brain 2007)
Voltage-gated sodium channel: activation (Lou, et al, J Physiol 2003)
Hyperpolarization is necessary for depolarization-induced sodium currents in pancreatic beta cells
Summary I • 1. VGSC currents are voltage-gated inward currents. • 2. VGSCs perform fast activation and fast inactivation. • 3. Inactivation and recovery of VGSCs are diverse.
Tetrodotoxin - Pufferfish Saxitoxin - Paralytic Shellfish Poisoning Soong, T.W. and B.Venkatesh.Trends Genetics, 22; 621-626 (2006)
TTX and STX- Molecular Mimics Soong, T.W. and B.Venkatesh.Trends Genetics, 22; 621-626 (2006)
Y/N substitution in Pufferfish = TTX resistant VGSC and binding site for TTX Soong, T.W., and B. Venkatesh, Trends Genetics, 22; 621-626 (2006)
Blocking of WT and mutant VGSCs by TTX and STX E/D mutation – TTX/STX-resistance blocking by TTX (a) and STX (b)Scale bars, 1 nA and 1 ms. Bricelj, V.M. et al., Nature, 434; 763-767 (2005)
O-conotoxin (MrVIB) selectively blocks Nav1.8 ---- TTX-resistant current in DRG TTX-resistant sodium channel (Nav1.8) No effect onthe persistent TTX-R Na current Nav1.9) Ekberg,J et al, PNAS(2006)
Summary II药理学--电压门控钠通道分类 • 神经类钠通道（对TTX敏感性高、对μCTX敏感性低） • 骨骼肌类钠通道（对TTX和μCTX敏感性均高） • 心肌类钠通道（对TTX和μCTX敏感性均低）。
Sodium channels co-immunoprecipitate with RPTPb Increase postnatally embryogenesis Constant levels Ratcliffe CF, et al. Nature Neuroscience 2000
Functional effects of BDNF on Nav1.2 channels (Ahn, et al, JNS 2007)
(Src family kinases)SFKs interact with and phosphorylate Nav1.2 (Ahn, et al, JNS 2007)
SH3 domain mediates the interaction between Nav1.2 and Fyn (Beacham et al JNS,2007)
Summary III • 1. VGSC are regulated with phosphatase and kinase • 2. Biochemical studies and physiological studies on VGSCs are put together.
Pain and Nav1.7 congenital insensitivity to pain 先天性痛不敏感症 Paroxysmal extreme pain disorder 突发性疼痛异常 erythromelalgia （原发性）肢端红痛症 Primary erythromelalgia PE
More SNPs 钾离子恶化性肌强直病,PAM 高血钾性周期性麻痹，HyperPP 先天性肌强直病，PMC
What can go wrong? permeation kinetics Na+ targeting translation assembly • Expression models • cRNA or cDNA injection into Xenopus oocytes • Transfection of mammalian cell culture • Methods • Electrophysiology • Pharmacology • Immunocytochemistry • Fluorescence imaging of tagged proteins
Take home messages • 1. Na channels physiological properties are diverse and crucial. • 2. Na channels are regulated by drugs, enzymes and single mutation of themselves.