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module 7: Local Anesthetic Mechanisms (Voltage Gated Sodium Channel (mech,…
module 7: Local Anesthetic Mechanisms
Voltage Gated Sodium Channel
structure
alpha subunit (2)
4 homologous domains per alpha
6 transmembrane helices:
s1-s6
connected by cytoplasmic or extra cell loops
S4 = open pore; sensitive to voltage changes
extracellular loops btwn S5/S6 = entrance; sodium selective
S6 of domains 1, 3, 4 = target of anesthetics
B-ScTx
bind tetrodoxin and sodium channel specific toxins
beta subunit (1 or 2)
stabilization of pore
mech
resting: H-gate open, m-gates closed
activated: H-gate open, m gates
inactivated: H gate closed, m gates open (refractory period)
regulation
access to binding site
preferential binding
LA bind open or inactivated channel
more charged LA --> bind cytoplasmic site
lipophilic/uncharged LA --> membrane
all maintain shut channel = blocked impulse
dependent block
freq dependent conduction block
phasic block
transitional block
wedensky inhibit
neuron excitiation
chem messengers at synapse
unidirectional dp
temp increase sodium conductance
depolarization before threshold = no nerve conductance