Sodium Revision Flashcards
First evidence that TTX was a NaV specific blocker
Sucrose Gap - Voltage clamp of lobster giant axons
94nM
no effect on K+ current
Narahashi, Moore and Scott, 1964
Structural determination
Tsuda 1964
Guanine
+ one positive charge at physiological pH
External block
TTX block outside nerve membrane
Blocking action devoid on internal perfusion
Narahashi, Anderson and Moore, 1967
Support of cationic block
Hille, 1975
Permeability titrates away at increasingly low pH owing to the presence of protons
TTX block in relation to gating
Keynes and Rojas, 1974
Measured gating currents of Nav not affected by TTX
Plugging blocks flow from outside even though gating mechanism normally operates upon depolarizing stimulation
One-to-one stochiometric block suggests
Q, Y + N, 1985
Characteristic of single ion channel not affected
Observation open decreases dose-dependently
Relative sizes of subunits
250
33-37
kDA
Hairpin P loop
S5-S6 of DIII
TTX binding sites
All S5-S6 of domains
u-Connotoxin binding site
Only S5-S6 of DII
NT binding site 2
S6 of DI and DiV
NT binding site 3
S3-S4 linker DIV
NT binding site 4
S1-2 linker DII
NT binding site 5
S6 DI and S5 DIV
Beta subunit important for
Voltage dependency gating cell adhesion signal transduction expression at PM
IFMT is where
Between DIII and DIV
S4 time course associates with
onset of inactivation or slow ON gating charge
Why is S4 not inactivating particle?
Goldshem-Ohm 2013 - inactivation deficient mutant -> movement leads to secondary conformational change exposes binding site for inactivating particle
Docking site consists of
S4-S5 DIII and DIV
CTD S6 DIV
Binding site has what type of residues?
Miyamoto 2001 - hydrophobic - allows phenyalanine at P1489 to interact with alanine in DIII S4-S5 and asparaganine DIV S4-S5
What does hair-pin structure do?
Sirota 2002 - optimizes interaction etween IFMT and docking site - outtward movement occurs around a hinge comprised of glycine and proline
What might underlie slow inactication
Capes 2013 - disable DIV S4 -> by introducing glutamine in the first 3 charge carrying residues -> slow entry and recovery from fast inactivated states
CNS Nav’s are
Nav1.3 fetal nervous system tissue
1.1 , 1.2 and 1.6 in adults
Where are 1.1 and 1.3 expressed and what does this indicate?
Soma of CNS neurons -> integrate synaptic impulses -> set AP initiaition and propagation to dendritic and axonal compartments
Nav1.2
expressed in unmyelination neurons - conducts AP - westenbroek 1989
Nav1.6
expressed in nodes of Ranvier in developing neurons - saltatory conduction - Boiko 2001
How many alpha subunits?
Yu and Catterall 2003 - 10 distinct pore-forming alpha subunits, 9 of which are functional
Nav1 contributes to
upstroke of AP
Nav1.4
skeletal respiratory muscle ECC
SCN4A mutants lead to
altered skeletal muscle excitability
- periodic paralysis
- congenital myopathy
- myasthenic syndrome
Cardiac current needs
rapid depolarization
Nav1.5 provides
fast, subsequent opening - ECC
re-open in plateau phase - late inward / persistent current -> viophysical proeprties of cardiac current
Where else is 1.1 + 1.6 expressed
in adult PNS
What is more expressed in PNS how was this found?
1.7, 1.8 and 1.9 -? cloned from sympathetic and DRG neurons
