strand 1 Flashcards
SCN9A
gene linked to human pain perception
mutations> channelopathies
secondary active transport
indirect coupling molecule with another moving along echem gradient
antiport/ symport
Na+-K+ ATPase
cytoplasmic Na+ binds
pump ATP-phosphorylated
conformation change (Na+ release)
extracel K+ binds (dephosphorylation)
pump returns to conformation (K+ release)
Na+-K+ ATPase ratio in and out
3 Na+ out
2 K+ in
experimental methods for ion channel investigation
patch-clamp electrophysiology (measure V change across PM)
(cryo) electron microscopy
X-ray crystallography
Vm
Vi-Vo
equilibrium potential
when ion flux in/out is balanced
Nernst equation
E ion= zF/RT ln( [ion] inside/[ion] outside)
simplified to > 61/z (log([ion]out/[ion]in)
shaker potassium channel
KCNQ1
Sh gene in drosophilia
a/b sub units
shorter lifespan and less sleep efficiency
closest human homologue of drosophilia Sh gene
KCNA3
gating types
ligand
voltage
mechanical
TTX
tetrodotoxin
blocks Na channels
ion channel structure investigation
amino acid structure> side chains predict structure
hydrophobic = transmembrane
hydrophilic = extramembrane
X-ray crystallography
crystallize, X-ray > e- density map > atomic model
positives of X-ray crystallography
any size molecule/ macromolecule
negatives of X-ray crystallography
may damage protein
may take years
cryo-electron microscopy
frozen in any state and microscopy
positives of cryo-electron microscopy
any size/ macro
near-atomic resolution
fastc
nuclear magnetic resonance
dissolved and radioactively labelled
negatives of nuclear magnetic resonance
larger molecules can’t be conserved
characteristics of ion channels difficult to crystallize
transmembrane
large
multi[ple conformations/ sub-units
dynamic and disordered
low solubility
alpha fold
future structure prediction of protein via databanks
:) rapid
no. homologue domains in K channel
4
Na+ trajectory/ elution
tortuous trajectory
slow elution
K+ trajectory/ elution
straight trajectory
fast passage
K channel selectivity filter
narrow selectivity filter
mutations can abolish selectivity
N-type channel inactivation
amino acid N-terminus occlude intracellular side of pore
rapid inactivation
C-type channel inactivation
hinged lid
conformational change at selectivity filter/ extracel entrance
slow inactivation
PETAFLOP
measurement unit for 10^16 complex operations per second
major extracellular ions
cations: K/Mg
anions: phosphate/ amino acids
major intracellular ions
cations: Ca/ Na
anions: Cl
RMP
-70mV
maintained via K+ leak channels and ATPase pumps
Action potential
rid change in RMP
sudden reverse in membrane polarity
stages of action potential
resting
depolarisation (-70> +30 mV)
repolarisation
hyperpolarisation
v-gated channels
Na+ enters
K+ leaves
Na+ gate threshold
-55mV
fast opening v-gated
automatic/ fast v-gated
slow/ automatic inactivation from closed
K+ gate closure
slow opening/ closure
absolute refractory period
no AP generated
Na+ channel inactivated
relative refractory period
AP generation w large stimulus
Na+ channels recovered
K+ channels still open
nociception
sensory nervous system’s process of encoding potentially harmful stimuli.
Mediated by ion channels
stimuli transduction
through nociceptors, transmitted up primary afferent nociceptor, modulated through interneurone, up spinothalamic tract into thalamus via thalamocortical projections then brain perception
nociceptor fibre types
A beta
A delta
C fibre
what do a beta fibres detect?
non-noxious mechanical stimuli
what do a delta fibres detect?
noxious mechanical stimuli
what do C fibres detect?
noxious heat and chemical stimuli
myelination of nociceptive fibres
a beta myelinated
a delta lightly myelinated
c is not myelinated
diameter of nociceptive fibres
a beta large
a delta medium
c is small
function of nociceptive fibres
a beta is proprioception
a delta is nociception
c is nociception
thermal threshold of nociceptive fibres
a beta has no thermal threshold
a delta is ~53 (type I) /47 C (type II)
c is ~43 C
transient receptor potential channels
ion channels responding to heat/acid/reactive chemicals/ enviro cold/ cold hyperalgesia
additive effects
acute vs chronic pain
acute <3 months
chronic > 3 months
pain classes
normal
inflammatory
neuropathic
somatic pain
peripheral nervous system
specific localisation
a delta and c fibres
pain-relief response
visceral pain
viscera (uterus/ intestine/ kidneys/ stomach)
non-specific region
a delta and c fibres
autonomic symptoms
poor pain relief response
inflammatory pain
macrophage/ mast cell/ neutrophil/ granulocyte regulated
treatment> COX2 inhibition
localized pain and swelling
persistent/ chronic nature
neuropathy
damage causing changes to expression/ post-trans mod of nociceptors
not easily repaired
v specialized
opioid/ anticonvulsants/ Na+ channel blocker/ NMDA antagonist
pain relief targets
nociceptors
NaV channels
pain relief issues w nociceptors
heterogeneous pain response
>1 nociceptor
redundancy
side effects
other tissue expression
BBB non-permeable to drugs
NaV channel target
alpha sub-unit at VGSC
at dorsal root ganglia
enrichment or exclusive depression
lidocaine
reversible binding to inner pore of V-gated Na+ channels in open/ inactivated states
greater affin for inactivated channels (not resting)
non-selective
cystic fibrosis
mutation to CFTR gene
Cl- influx dysfunction
mucus accumulation and inflammation
genetic linkage
monogenic/ autosomal recessive
100% penetrance
class I CF mutation
no CFTR from mRNA
class II CF mutation
protein folding and trafficking failure
class III mutation
gating failure
class IV mutation
decreased stability at membrane
class V mutation
insufficient CFTR quantities
linkage mappong
mendelian inheritance pattern of single gene trait
segregated trait in fam
map SNP to locus
SCN9A gene voltage gate
1.7 NaV
expressed by dorsal root ganglia sensory neurone
contributes to rising phase
amplifies subthreshold stimuli
TTX responsive
fast kinetics
paroxysmal extreme pain disorder
autosomal dominant
severe pain in rectal/ ocular/ mandible
chewing/ heat triggers
childhood onset
impaired inactivation
inherited erythromelalgia
autosomal dominant
burning pain in hands and feet
exercise/ heat triggers
childhood onset
enhanced activation
small fibre neuropathy
loss of function
autosomal dominant
inherited erythromelalgia mutation
L858H mutation in 2nd domain
lowers activation threshold therefore NaV1.7 open more readily to smaller depolarizations prolonged channel opening due to slow inactivation
^ramp response
shift v-dependence of in/activation for ^hyperpolarized potential inactivation
PEDP mutation
decreases channel activation threshold
delayed channel inactivation
^ response to repetitive stimulation
CIP
complete insensitivity to pain
complete insensitivity to pain
autosomal recessive
complete sensation loss
non-sense mutations in domains 1/11
premature stop codon > truncated protein
therapies for complete insensitivity to pain
small molecules mimicking toxin binding (belter PK/PD)
botox *doesn’t target NaV