Voltage-gated sodium channelsXiao YuInstitute of PhysiologyShandong University, School of Medicine2012-11-10

Sodium channel genes are latecomers to the 6TM Family(Zakon HH, PNAS 2012)

Sodium Channels - StructureComposed of , -1 and -2 subunits, but the large -subunits carries most of the functional properties 4 repeated motifs, each with 6 transmembrane domainsAll linked togetherContain 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

Outline1. Physiological studies

2. Pharmacological studies

3. Biochemical studies

4. Pathological and further studies

Ion channelsGates Voltage 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 I1. VGSC currents are voltage-gated inward currents.

2. VGSCs perform fast activation and fast inactivation.

3. Inactivation and recovery of VGSCs are diverse.

Tetrodotoxin - PufferfishSaxitoxin - Paralytic Shellfish PoisoningSoong, T.W. and B.Venkatesh.Trends Genetics, 22; 621-626 (2006)

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)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)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

--

TTXCTXTTXCTXTTXCTX

Sodium channels co-immunoprecipitate with RPTPbIncrease postnatallyembryogenesisConstant levelsRatcliffe CF, et al. Nature Neuroscience 2000

Sodium channel a 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 III1. VGSC are regulated with phosphatase and kinase

2. Biochemical studies and physiological studies on VGSCs are put together.

Anosmia ---- loss of smell ()

Channelopathy

Pain and Nav1.7congenitalinsensitivity to pain erythromelalgiaPrimary erythromelalgiaPE Paroxysmal extreme pain disorder

More SNPsHyperPPPMC,PAM

Na+translationassemblytargetingkineticspermeationWhat can go wrong?Expression models cRNA or cDNA injection into Xenopus oocytes Transfection of mammalian cell cultureMethods Electrophysiology Pharmacology Immunocytochemistry Fluorescence imaging of tagged proteins

Take home messages1. Na channels physiological properties are diverse and crucial.2. Na channels are regulated by drugs, enzymes and single mutation of themselves.

Thanks!

*