Voltage-gated sodium channels

Xiao YuInstitute of Physiology

Shandong University, School of Medicine2012-11-10

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

Human voltage-gated sodium channels: Genes and proteins

Outline

• 1. Physiological studies

• 2. Pharmacological studies

• 3. Biochemical studies

• 4. Pathological and further studies

Ion channels—GatesVoltage gated sodium channels (VGSC)

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

Steady-state inactivation/availability of VGSC

Kinetics of inactivation differs in b cells and ACCs

Time course of VGSC recovery: b cells are slower than ACCs

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

Y/N substitution in Pufferfish = TTX resistant

Soong, T.W., and B. Venkatesh, Trends Genetics, 22; 621-626 (2006)

VGSC and binding site for TTX

blocking by TTX (a) and STX (b) Scale bars, 1 nA and 1 ms.

Bricelj, V.M. et al., Nature, 434; 763-767 (2005)

E/D mutation – TTX/STX-resistance

Blocking of WT and mutant VGSCs by TTX and STX

TTX-resistant sodium channel (Nav1.8)

No effect onthe persistent TTX-R Na current Nav1.9)

Ekberg,J et al, PNAS (2006)

O-conotoxin (MrVIB) selectively blocks Nav1.8 ---- TTX-resistant current in DRG

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 RPTP

Increase postnatally

embryogenesis

Constant levels

Ratcliffe CF, et al. Nature Neuroscience 2000

Sodium channel subunits are tyrosine phosphorylated

Phosphatase-Sodium channel-Kinase

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.

Anosmia ---- loss of smell ( 嗅觉缺失 )

Channelopathy （离子通道病）

2006 Dec 14;444(7121):894-8.

Pain and Nav1.7

congenitalinsensitivity to pain先天性痛不敏感症

erythromelalgia（原发性）肢端红痛症Primary erythromelalgiaPE

Paroxysmal extreme pain disorder 突发性疼痛异常

More SNPs

高血钾性周期性麻痹， HyperPP

先天性肌强直病， PMC

钾离子恶化性肌强直病 ,PAM

Na+

translation assembly

targeting

kinetics

permeation

What can go wrong?

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.

Thanks!