Ion Channels and Pain Flashcards
5 receptor types
Lipid-soluble ligand Enzymatic reaction Tyrosine Kinase activation Ion channel activation G protein-coupled receptor
Ion channels provide a _____ route for ions through _____ _____ membranes
Permeable
Hydrophobic lipid
Ion channels consist of ____ folded into ________
amino acids
complex structures
Ion channels are made from 3-6 similar ______ or ______
proteins
structural subunits
Can ion channels be selective to specific ions? non-selective?
Yes
Yes
Definition of gating
open and close in response to specific chemical, electrical or mechanical signals
Ion channels conduct ions across _____________
plasma membrane
Ion channels regulate ________ ________ of cells
membrane potential
5 types on ion channels
Resting K+ channel Voltage-gated channel Ligand-gated channel Signal-gated channel Mechanically-gated channel
Ions that cross through voltage-gated channels?
Na+, K+, Ca2+, Cl-
How many transmembrane segments are in the voltage-gated ion channels?
6
Voltage-gated ion channels open in response to changes in what?
membrane potential
2 domains in voltage-gated ion channels?
Voltage sensor domain (S1-4) Pore Domain (S5-6)
3 major superfamilies on Ligand-Gated Ion channels?
Cys-Loop Receptors
Ionotropic Glutamate Receptors
P2X Receptors
Ligand-Gated Ion Channels : transmembrane domains are important for? (2)
pore formation
ion selectivity
Ligand-Gated Ion Channels : what is important for ligand binding? (determines which ligand can bind to it)
extracellular domains
Extracellular domain of Cys-Loop receptors?
Disulfide bridges of cysteine residues
Extracellular domain of Ionotropic Glutamate receptors?
Ligand binding domain (segment and 2)
N-terminal domain
Two ways a cell can sense a mechanical stimuli?
Direct gating by physical opening of channel
Indirect by activation of GPCR then opening of TRP channels
What happens in regard to action potential when activating a ligand-gated ion channel?
Opening, Na+ influx, nerve depolarisation
Effect of a mild mechanical stimulation
Opening of only a few ion channels, but firing isn’t highly activated, relatively few action potentials
Effect of noxious mechanical stimulation
Many ion channels open, nerve firing probability increased and multiple action potentials can be generated which means more firing of the nerves
Effect of noxious mechanical stimulation
Many ion channels open, nerve firing probability increased and multiple action potentials can be generated which means more firing of the nerves
Resting membrane potential value?
-70mV
Which complex helps the transport of cations and anions to normalize the membrane potential?
Na+/K+ exchange pump
Concentration gradients of Na+ and K+ in extracellular and intracellular?
Extracellular:
K + 4.5 mM
Na+ 145 mM
Intracellular
K+ 120 mM
Na+ 15 mM
What causes sodium to enter channel? what happens to action potential?
stimulus
depolarization (spike in voltage)
When sodium leave the cell and ion channel closes, what happens to action potential? What does this do to ADP-ATP?
repolarization
Exchange ATP for ADP
Example of Cys-Loop Channel?
Nicotinic Ach Receptor
Nicotinic Ach Receptor : subunits?
two alpha
one beta
one gamma
one delta
Nicotinic Ach Receptor requires how many Ach molecules for activation? Which ion influxes once the pore opens
2
Na+
Nicotinic Ach Receptor functions? (4)
- Skeletal muscle contraction
- Smooth muscle relaxation
- Inhibits cardiac muscle contraction
- Nerve depolarization
What dictates the location and pharmacology of Nicotinic Ach Receptors?
Subunit composition
What causes depolarizing blockade? (Nicotinic Ach Receptor)
Excess Ach and Nicotinic Receptor Agonists
Depolarizing blockade : what are the effects of continuous activation of nicotinic receptors?
Muscle excitation and fasiculations in myocytes and then flaccid paralysis
Depolarizing blockade : what are the effects of prolonged agonist bound nAchRs?
neuron desensitization
Depolarizing blockade : what are the effects of continuously depolarized membrane?
Affects inactivation of voltage-gated sodium channels (nerve less likely to fire)
nAch Receptors located where?
DRG
Dorsal horn of spinal cord
Ach sensitizes about 50% of ___ fibres for heat but not ________ pain
C
mechanical
Analgesics for nAch Receptors and Pain? (4)
They inhibit what? (2)
Botulinum toxin, alpha-7 blockers, epibatidine, nicotine
Inhibits inflammatory neuropeptide and cytokine release
GABAARs Cys-Loop Receptor : what type of receptor? allows passage of what ion?
Inhibitory (hyperpolarization)
Cl-
Composition of GABAAR?
Heteropentameter with variable subunits
GABAARs activated by what?
GABA
GABAARs are found where?
Dorsal horn of spinal cord
Roles of GABAAR? (2)
Inhibits pain transmission by hyperpolarizing second order neurons
Inhibits substance P release form primary afferent neurons
Which drugs potentiate GABA-mediated synaptic inhibition? (2)
Benzodiazepines
Barbiturates
GABA binds where on GABAAR?
alpha-beta interface
Benzodiazepines binds where on GABAAR?
alpha-gamma subunit interface (allosteric binding site)
Barbiturates interacts with what on GABAAR?
Pockets in the transmembrane domain
Acute pain?
warning system for harmful stimuli
chronic pain lasts more than _____ months and it is __________
3
maladaptive
the Nervous system can change in response to pain because it is _______
plastic
4 steps to the pain pathway
- Nociception
- Neurotransmission
- Sensation, Cognition, Emotion
- Neuromodulation
5 types on fibres in the sensory nerves
Which one is unmyelinated?
Biggest to smallest diameter?
Biggest to smallest conduction velocity?
A-alpha A-beta A-gamma A-delta C - unmyelinated
From top to bottom :
- biggest to smallest diameter
- fastest to slowest conduction velocity
Function of A-alpha fibre
proprioception
Function of A-beta fibre
mechanosensation
Function of A-gamma fibre
Motor fibre to muscle spindle
Function of A-delta fibre
mechanosensation nociception
Function of C fibre
temperature nociception
3 types of pain
Nociceptive
Inflammatory
Neuropathic
5 factors that activate nociceptors
Mechanical Heat Cold Pathogens Chemical
What activates TPRV1 and what does this lead to?
Capsaicin
Mustard Oil
Formalin
H+
Opens channel, Na+ an Ca2+ enter free nerve ending, depolarisation
What causes neuropathic pain in the periphery? (4)
Trauma
Metabolic
Infection
Chemo induced neuropathy
What causes neuropathic pain centrally?
Spinal cord injury
Stroke
Multiple sclerosis
3 classes on analgesics
Non-opioid analgesics
Opioid analgesics
Adjunct analgesics
3 types of adjunct analgesics
Anti-convulsants
Anti-depressants
Biologics
3 types of anti-depressants
TCAs
SSRIs
SNRIs
TCAs are highly effective for _____ neuropathic pain
chronic
Example of a TCA and what is their MOA?
Amitriptyline
Blocks neuronal uptake of NA and 5-HT in spinal cord, increases descending inhibition
Also blocks NMDA receptors, Na, K, Ca channels
What is the major effect of Amitriptyline (TCA)?
Analgesic effect is independent of mood change
Examples of SNRIs? (2)
Duloxetine
Venlafaxine
Examples of SSRIs?
Fluoxetine
Fluvoxamine
SSRIs have fewer side effects because of ___________
high selectivity
SSRIs have low efficacy for __________ neuropathic pain
diabetic
SNRIs have fewer side-effects than TCAs because they __________________
do not block NMDA receptors
More efficient : TCA, SSRIs of SNRIs?
TCA > SNRI > SSRI
More side effects : TCA, SSRIs, or SNRIs>
TCA > SNRI > SSRI
anti-convulsants are used for ______ and they interfere with _______
epilepsy
neuronal excitability
2 examples of anticonvulsants?
Effective for which diseases? (3)
Side effects? (4)
gabapentin
pregabalin
Postherpetic neuralgia, diabetic neuralgia, fibromyalgia
Side-effects : drowsiness, dry mouth, weight gain, dizziness
MOA of gabapentinoids?
What does it inhibit?
It also modulates what?
MOA : binds to alpha-2-delta subunit of Ca2+ channel
- Inhibits release excitatory NTs
- Also modulates Na, K activity : altered neuronal excitability
Gabapentin is given ___
locally
Gabapentin reduced _____ in normal AND inflamed joints
mechanosensitivity
In inflamed joints, gabapentin doesn’t seem to reduce __________
neuronal activity
is gabapentin ideal for inflammatory pain?
No
Inflammation may alter gabapentin binding to what?
alpha-2-delta subunit of Ca2+ channel
Na+, K+ and Ca2+ are involved in nerve ________ and _______.
Also in electrical _________ along ______
depolarization
communication
transmission
axons
Voltage-dependent conformational change in ion channels results in what?
open state
Voltage-gated Sodium Channels (VGSC) :
Classification of VGSC?
Derived from what?
Tetrodotoxin (TTX)
Derived from puffer fish
TTX sensitive channels are found where? (2)
Muscle, CNS
TTX resistant channels are found where?
Some sensory neurones
Types of VGSC? (9)
Nav1.1-Nav.9
Which VGSC isoforms are involved in nociception?
Nav1.7, Nav1.8 and Nav1.9
Which Nav isoforms are predominantly in the CNS?
Nav1.1, Nav1.2 and Nav1.3
Where is Nav1.4 found? What is their role?
skeletal muscle
skeletal muscle contractility
Where is Nav1.5 found? What is their role?
Heart
Cardiac function
Where is Nav1.6 found?
Mainly in large diameter neurons, motor neurons, also in CNS
Where are Nav1.7, Nav1.8 and Nav1.9 found?
PNS
Which Nav isoforms have a slow inactivation rate?
Nav1.8 and Nav1.9
Which Nav isoforms have a low TTX sensitivity?
Nav1.8 and Nav1.9
Which Nav isoform has an intermediate TTX sensitivity?
Nav1.5
Which Nav isoforms are brain type sodium channels and unlikely to be involved in pain?
Nav1.1, Nav1.2, Nav1.3, Nav1.6
Role of Nav1.7?
Peripheral sodium channel subtype. Excellent target for pain control
Role of Nav1.8? (3)
- Action potential electrogenesis
- Redistribution along intact axons after nerve injury may promote sensory hypersensitivity
- Excellent target for pain control
Role of Nav1.9?
May modulate resting potential of DRG and response to subthreshold stimuli.
Nav1.7 gain of function disease?
Mutation in SCN9A gene
Familial erythromelalgia
Burning, intense pain
Nav1.7 loss of function disease?`
Loss of function of SCN9A gene
Congenital insensitivity to pain
Self harm, unknown injuries
What is a local anaesthetic that acts on sodium channels?
Does is activate or inactivate Na channel?
Where does it bind?
Is it selective?
Lidocaine
Inactivation
Intracellular pore
Not selective
What is an antidepressant that acts on sodium channels?
Inactivate or activate Na channel? Where does it bind?
Is it non selective for ______ subtypes so it can affect _____ and _____ activity
- Amitriptyline
- Interacts with local anaesthetic binding site and binds to inactivated channel, keeps them in inactive state
- Na+ channel subtypes
- Cardiac and skeletal muscle
What is an anticonvulsant that acts on sodium channels?
It inhibits which Na+ channels? (2)
Non-selective for _____ subtypes so can affect _____ and ______ activity
Carbamazepine
Binds to inactive channel, keeping them in inactive state
-Inhibits TTX-resistant and TTX-sensitive Na+ channels
-Na+ channel subtypes
-Cardiac and skeletal muscle activity
When testing NON-SELECTIVE VGSC blockers, do we get negative or positive side-effects?
Negative
Ex: cardiac arrhythmias
When testing Nav1.8 blocker on joint pain, does it increase or decrease pain?
decrease
Where do Nav1.8 blockers act?
in periphery
Cav1.1 - Cav1.4
Tell me their current, inactivation and tissue localization
Cav1.1 : L, Fast, skeletal muscle
Cav1.2 : L, Fast, Cardiac Myocytes and Neurons
Cav1.3 : L, Fast, Cardiac Myocytes and Neurons
Cav1.4 : L, Fast, Retinal Cells
Role of Cav1.1
Excitation contraction coupling
Role of Cav1.2
Excitation-contraction coupling
Synaptic integration
Role of Cav1.3
Cardiac pacemaker
NT release
Role of Cav1.4
NT release from photoreceptors
Cav2.1-2.3
Tell me their current, inactivation and tissue localization
Cav2.1 : P/Q, Slow, Neurons
Cav2.2 : N, Slow, Neurons
Cav2.3 : R, Slow Neurons
Role of Cav2.1
NT release
Role of Cav2.2
NT release
Role of Cav2.3
Nerve firing
Cav3.1-3.3
Tell me their current, inactivation and tissue localization
Cav3.1 : T, Fast, Neurons and Cardiac Myocytes
Cav3.2 : T, Fast, Neurons and Smooth muscle
Cav3.3 : T, Fast, Neurons
Role of Cav3.1
Repetitive Nerve firing
Cardiac pacemaker
Role of Cav3.2
Repetitive Nerve firing
Contractile response
Role of Cav3.3
Repetitive Nerve firing
Name 2 L-Type drugs that act of calcium channels
What do they do?
Nifedipine
Verapamil
Decrease substance P release and pain
Name 2 N-type drugs that act on calcium channels, what do they do?
conotoxin : decreases substance P release and pain
Knockout animals : decreases inflammatory and neuropathic pain
Name a P/Q type drug that acts of calcium channels
What does it do?
agatoxin : decreases substance P release and migraine
Name a R type drug that acts of calcium channels
What does it do?
SNX-482
Decreases substance P release
Name a T type drug that acts of calcium channels
What does it do?
Mibefradil
decreases pain
How is a voltage gated calcium channel classified?
How is it subclassified?
Classified based on type of voltage required to activate them
Subclassified based on alpha-1 pore forming subunit structure and pharmacological properties