Module 2 Lecture 4 Flashcards
what is the principle subunit of Cav
alpha or alpha1 subunit (resemble the Nav alpha)
what is the alpha/alpha1 subunit responsible for in Cav
gating and conduction
what is the alpha subunit composed of in Cav
four repeat domains covalently linked together
- each domain has 6 TM sequences
- S4 = voltage sensor, S5 S6 = pore, w/ S5-S6 linker
what are the ancillary subunits in Cav
alpha2-delta, beta, gamma
what is alpha2-delta in Cav
two separate proteins (encoded by the same gene) - mostly extracellular, site of Gabapentin action
- traffcking and putting voltage-gated Ca channels in the right spot
Gabapentin function
interferes and reduces amplitude of Ca current
- diminish neuronal activity
beta subunit characteristics in Cav
intracellular & covalently bound to alpha, impacts voltage dependency
gamma subunit characteristics in Cav
integral membrane protein; mostly found in muscle fibers
characteristics of voltage-dependent peak Ca2+ current
similar to sodium but with Ca reversal potential
how does voltage affect inactivation in Cav2.1
as voltage increases, inactivation becomes more likely
role of glutamate in calcium channel
glutamate (E) amino acid residue lines each pore loop; form 4 pockets/binding sites w/ high affinity for Ca2+
- if another Ca2+ ion comes along, it pushes one through and occupies the binding site
what did mutation of the P-loop glutamate (E) to alanine (A) do
decreased inward current during depolarization and reduced tail current
what is the most diverse group of ion channels
potassium-selective channels
characteristics of a functional K+ channel subunits
heteromultimeric assembly of alpha (pore-forming) subunits
- can be homotetramers or heterotetramers
sources of K+ channel diversity
alternate mRNA splicing, post-translational modification, heteromultimeric association with modulatory subunits
types of small-molecule neurotransmitters
acetylcholine, amino acids, biogenic amines
types of amino acid neurotransmitters
glutamate, GABA, glycine
types of catecholamines (biogenic amines)
dopamine, norepinephrine, epinephrine
types of biogenic amines (not catecholamines)
serotonin, histamine
when was ACh discovered
Vagus-stoff 1921, CNS action late 40s, early 50s
when were adrenaline and noradrenaline discovered
mid 50s
when was GABA (glycine) discovered
50s-60s
when was glutamate discovered
70s, early 80s
when was nitric oxide discovered
90s
when were endo-cannabinoids discovered
early 00s
acetylcholine primary function
muscle control, memory formation, sensory response
- excitatory
ACh locations
neuromuscular junctions, CNS
ACh receptors
nicotinic, muscarinic
serotonin primary function
intestinal movement control, mood regulation, appetite, sleep, muscle control
serotonin locations
gut, CNS
serotonin receptors
5-HT
dopamine function
reward pathways, cognition, voluntary motion
dopamine location
hypothalamus
dopamine receptors
D1, D2, D3, D4, D5
norepinephrine function
fight or flight response
norepinephrine locatino
adrenal medulla
norepinephrine receptors
andrenergic
L-DOPA function
precursor to dopamine
L-DOPA locatino
hypothalamus
tryptophan function
precursor to serotonin
tryptophan location
blood
GABA function
inhibits CNS
GABA location
brain
GABA receptors
GABAA, GABAB
glycine function
inhibits signals
glycine location
spinal cord, brainstem
glycine receptor
NMDA
tyramine function
blood pressure regulation
tyramine location
CNS, kidney
tyramine receptor
TA1
glutamate function
long term potentiation, memory
glutamate location
CNS, PNS
glutamate receptor
NMDA, others
2 major classes of transmission
- ionotropic (ligand-gated ion channels)
- metabotropic (G-protein coupled receptors)
steps of ligand-gated ion channels
- neurotransmitter binds
- channel opens
- ions flow across membrane
steps of GPCR
- neurotransmitter binds
- G-protein activated
- G-protein subunits or intracellular messengers modulate ion channels
- ion channel opens
- ions flow across membrane
nACh receptor subunits
alpha 1-10, beta 1-4, gamma, delta, epsilon
AMPA receptor subunits
GluA1, GluA2, GluA3, GluA4
NMDA receptor subunits
GluN1, GluN2A, GluN2B, GluN2C, GluN3A, GluN3B
kainate receptor subunits
GluK1, GluK2, GluK3, GluK4, GluK5
GABA receptor subunits
alpha 1-6, beta1-3, gamma1-3, delta, epsilon, theta, …
glycine receptor subunits
alpha1-6, beta
construction of native receptors
heterommultimers, but can be expressed as homomultimers in special circumstances
- all of the ligand-gated subunits can function as part of the pore
alpha-bungarotoxin
known to induce paralysis and prevent neuronal activation of muscle
structure of Torpedo californica and Electrophorus electricus channels
- 5 subunit proteins
- heteromeric or homomeric
characteristics of the nAChR subunits
native channels are heteromultimers of 5 subunits
- each subunit has 4 TM domains (M1-M4)
what subunits do muscle nAChR channels express
alpha, beta, gamma, delta, and epsilon
what subunits do brain nAChR channels express
combinations of neuron-specific alpha and beta subunits
characteristics of alpha subunits in nAChR channels
have a cysteine loop for gating (member of Cys-Loop superfamily, along with glycine, GABAA, and 5-HT3)
what is the cysteine loop important for in the nAChR channel
binding of ACh and gating of the channel
is the nAChR mostly intracellular or extracellular
extracellular
what forms the nAChR pore
M2
what happens upon ACh binding at two alpha subunit cysteine loops at 2 crucial tryptophan residues
M2 tilts and twists outward
- this opens the pore and causes displacement/shifting of subunits (particularly beta subunits)
vestibule function in nAChR
contain negatively charged amino acids – selecting for cations
what ions does nAChR generate
mixed current
why does nAChR generate a mixed current
pore is larger than of any voltage-dependent ion channels so far
- when in the closed conformation, too narrow for fully hydrated ions, but no carbonyl backbone to replace hydration cage
- when in the open conformation, accepts fully hydrated cations
how does signal to noise ration change throughout development
increases
what is the composition of nAChR early in development
lots of nAChRs composed of alpha, beta, delta, and gamma subunits
- smaller single-channel conductance
- slower gating (longer open)
what is the composition of nAChR as an adult
gamma subunit is replaced with epsilon
- larger single-channel conductance
- faster gating
what happens when you mutate the 3 rings of negative charges surrounding the pore
reduces conductance, but not selectivity
what ions does WT homomeric alpha 7 conduct
cations
what ions does WT GABAA R conduct
anions
what ions does mutated AChR conduct
aniona (switched 3 amino acid residues)
what do ligand gated AChR and GABAA - R have in common
- members of the Cys-loop superfamily
- usually heteropentamers
- M2 lines the pore
- ring of negatively charged amino acids around the pore does not control cation/anion specificity
what does selectivity depend on in ligand gated AChR and GABAA - R
3 other amino acids within the pore region
subunits of GABAA
usually 2 alpha, 2 beta, and 1 gamma or delta subunit
what are the three gene families for ionotropic glutamate receptors
AMPA, NMDA, Kainate
characteristics of receptors in ionotropic glutamate receptors
- native receptors are heterotetramers
- in expression systems certain receptors can function as homotetramers
AMPA receptor function
mediate the majority of fast excitatory transmission in the brain
- usually heterotetramers with 2 GluA1 and 2 GluA2 subunits
NMDA receptor function
coincidence detectors
- play a special role in synaptic plasticity
glutamate role in ionotropic glutamate receptors
agonist at all families
- AMPA, NMDA, or Kainate are agonists only for their respective families
what are the three domains of the GluA1 subunit
- amino-terminal domain (ATD)
- ligand-binding domain (LBD)
- transmembrane domain (TMD)
forms an asymmetrical Y-shaped protein
what are the transmembrane domains of the GluA1 subunit
M1-M4 TM regions
M2 characteristics in GluA1 subunit
p-loop, forms the pore
what are the sites for alternative splicing in GluA1 subunit
flip/flop (M3/M4 linker), and mRNA editing (Q/R - M2 and R/G - M3/M4)
what is the effect of binding of glutamate to LBD
causes the ‘clamshell’ orientation of the ATD and LBD to close, leading to movement of the gate and opening of the pore
ion selectivity of glutamate receptors
all glutamate receptors conduct Na+ and K+
NMDA receptor ion selectivity
Ca2+, Na+, and K+
AMPA receptor ion selectivity
do not conduct Ca2+ if the GluA2 subunit is present
what are the most common AMPA receptors
GluA1+2 and GluA2+3
conductivity for Ca2+/Na+, K+ in GluA1/GluA2
0.05
conductivity for Ca2+/Na+, K+ in GluA1
2
conductivity for Ca2+/Na+, K+ in GluN1/GluN2A
3-11
conductivity for Ca2+/Na+, K+ in GluN1/GluN2B
17
conductivity for Ca2+/Na+, K+ in GluN1/GluN2C
2
function of heterotetramers composed of GluA1, GluA3, and GluA4 subunits (GluA2-lacking AMPARs)
conduct Na+, K+, and Ca2+
- inwardly rectifying current
- PCa2+/PNa = 1-3
function of heterotetramers composed of GluA1 and GluA2 subunits (GluA2-containing AMPARs)
conduct only Na+ and K+
- PCa2+/PNa = 0.001 - 0.005
