Module IV - Lecture 1 - Secondary Messengers and Metabotropic Receptors Flashcards
In what two ways can neurotransmitter actions be divided into according to the way in which receptor and effector functions are coupled?
- direct gating - something binds and it opens (fast)
- indirect gating - an NT binds to a metabotropic receptor and this activates a G protein complex which has an alpha subunit and a beta gamma subunit and this can open or close another ion channel or there are receptor TKs and the subunits come together when an NT is bound and they phosphorylate each other and this influences the gating of another channel (slow)
What GABA receptor is metabotropic and which one is ionotropic?
GABAb - metabotropic
GABAa - ionotropic
Which of the metabotropic glutamate receptors mGluRs use Gq (aka IP3, DAG)?
mGlu1
mGlu5
Which of the metabotropic glutamate receptors mGluRs use Gi (aka decrease cAMP)?
mGlu2
mGlu3
Which of the metabotropic glutamate receptors mGluRs use Gs (aka increase cAMP)?
mGlu4
mGlu6
mGlu7
mGlu8
What is the name of the GPCR for ACh?
muscarinic ACh
What is the name of the GPCr for adrenalin?
adrenergic receptor
What is the common sequence followed by GPCRs which follow a common sequence?
First messenger - NT
Receptor
Transducer (G-protein) + Primary Effector (G protein target)
Second messenger (molecule made by enzyme) +
Secondary effector (molecule’s target)
What are the four different families of G proteins?
G alpha s
G alpha i
G alpha q
G alpha 12/13
What does G alpha s do?
-activates AC
-increases cAMP
-activates PKA
What does G alpha i do?
-inhibits AC
-decreases cAMP activation
What does G alpha q do?
-activates PLC
-produces release of Ca from intracellualr stores
What does G alpha 12/13 do?
-influences actin regulatory proteins
What does Gs - GPCR activate?
cAMP cycle
What is the cAMP Gs activated cycle involved in?
smooth muscle relaxation
bronchodilation
vasodilation (more blood to muscles)
What are mutations in the beta adrenergic receptor believed to cause?
asthma
What happens when norepinephrine or noradrenalin binds to a the beta adrenergic receptor?
the transducer Gs activates the primary effector adenylyl cyclase and this then generates the secondary messenger cAMP which activates the secondary effector cAMP dependent PKA
and PKA goes to phopshoyrlate ion channels and the amplitude of the NT induced EPSPs is increased and the neuron is more excitable
When the transmitter binds to a Gs GPCR what does the conformation of the receptor expose?
the Gs protein binding site
What does diffusion in the bilayer lead to the association of and the exchange of?
the association of the transmitter receptor complex with the Gs protein and this activates it for GTP-GDP exchange
What does displacement of GDP with GTP cause?
causes the alpha subunit to dissociate from the Gs complex and exposes a binding site on the alpha subunit for AC or adenylyl cyclase
What does the alpha subunit bind to and activate?
the cyclase to produce many cAMP molecules
What does hydrolysis of GTP by the alpha subunit cause?
it returns the subunit to its original conformation which causes it to dissociate from the cyclase and the cyclase becomes inactuve and the G alpha subunit reassociates with the beta gamma subunit
How long it the activation of the cyclase repeated?
until the dissociation of the transmitter return the receptor to its original conformation
What are ionotropic receptors composed of?
many proteins that come together and form a pore
What are metabotorpic receptors composed of?
one long protein with 7 TM domains and the NT binds to the NT binds to the EC region and the loop gets presented which is between the fifth and sixth TM domain in orange which allows for the association of G alpha beta gamma with the receptor
What does the cAMP pathway activate?
PKA and PKA has enzymatic or catalytic subunits and regulatory subunits
What is needed for PKA to be activated?
cAMP needs to bind to its regulatory subunit while the catalytic subunits need to unbind and go phopshorylate ser thr and tyr residues
What does G alpha i do?
it blocks the G alpha s pathway
What system do G alpha q proteins regulate?
the phosphoinositol system
What is the transducer in the phopshpinositol system?
G alpha q
What is the primary effector of the phosphoinositol system?
PLC(Beta)
What are the two secondary messengers in the phosphoinositol system?
IP3 and DAG
What is the secondary effector of the phosphoinositol system?
IP3 causes calium release from SER
DAG activates PKC
What do type I muscarinic receptors do?
hydrolyze phospholipids through the PLC system
What happens when ACh binds to the alpha q receptors?
the G alpha q subunit dissociates and goes to activates PLC which cleaves PIP2 (a phospholipid in the plasma membrane) into IP3 and DAG
What does IP3 do?
seeks out IP3 receptors on the smooth er and you do not want calcium in the cytoplasm for too long so the smooth er has calcium pumps to suck up calcium and store it inside the cells
What does the calcium released from the smooth ER do?
it binds to calmodulin and camKII
-when it binds to calmodulin it activates a calcium dependent kinase which has the same clam shell conformation that is opened with calcium and calmodulin and then goes and phosphorylates whatever proteins are in the vicinity
What does DAG do?
stays in the membrane and activates OPKC which has a clamshell autoinhibition regulation and DAG binds to the regulaotry subunit and allows PKC to binds to the membrane and phosphorylate proteins
What are the three major second messenger cascades of the phosphoinsitol system?
-IP3 binds to IP3 receptors and causes calcium release from intracellular stored
-DAG binds to and activates PKC
-calcium can bind to calmodulin and activates the calcium calmodulin dependent kinases
What do mGluR5 receptors work through?
the use of G alpha q
Where is mGluR5 located and what happens when you activate it?
-it is located at synapses and when you actuvate it the G alpha q causes a release of calcium from smooth er and get actiavtion of pkc which phosphorylates many proteins which are capable of communicating with the nucleus of neurons and can affect gene transcritpion and protein tramslation ad the affect of glutamatergic synapses and can increase mRNA produciton and protein translation in the nucleus which can result in endocytosis of AMPA receptors causing them to decrease
What is disrupted is fragile x syndrome and what happens and how can you treat this?
mGluR5 is disrupted in the syndrome
-this syndorme is under ASD and these people have a language delay and repetitive behavior and these individuals cause a result in fMRP function or mutations in the fMRP gene and this is a repressor of protein translation inhibiting the production of proteins from mRNA and lose this get more proteins that cause endocytosis so get less AMPA receptors
-can treat this by inhibiting mGluR5
What is an m type potassium channel and what does it do at cholinegric synapses?
if PIP2 is uncleaved it is bound to this potassium channels and the channel is open but if PIP2 is cleaved by PLC via G alpha q activation then the potassium channel closes and there is depolarization
What happens if an NT is bound to an ionotropic nicotninc ACh receptor?
the NT binds and sodium comes in
What happens to the m type potassium channel in the muscarininc receptor for ACh if you put in a small depolairzation in the cell?
nothing happens the current is zero because it will not want to close and depolarize the cell cause it is already posiitve
Do depolarization produced by a metabotopric mechanism cause an AP?
rarely but can increase the likelihood that subsequent fast EPSPs cause an AP
-get a depolarization of the membrane potential - this cause the membrane potential of the postaynptic neuron to be elevated for a period of time so in the absence of muscarine then can stimulate these neurons and get one AP but if you put on muscarine to activate these you get a bunch of AP and they influence the excitability of a neuron
What is the resting membrane potential of a neuron based on?
the asymmetric distrubution of sodium and potassium ions and the selectuve permability of the neuronal membrane to potassium
What ion channels are involved in an EPSP caused by opening a channel, which it the effect in membrane conductance, does it contribute to an AP, what is the time course, is there a second messenger, and what is the nature of synaptic action?
ion channels - non selective cation channel
membrane conductance - increase
AP - trigger AP
time course - fast (ms)
second messenger - none
nature - mediating or causing
What ion channels are involved in an EPSP caused by closing a channel, which it the effect in membrane conductance, does it contribute to an AP, what is the time course, is there a second messenger, and what is the nature of synaptic action?
ion channels - potassium channel
membrane conductance - decrease
AP - modulate AP
time course - slow (sec or minutes)
second messenger - cAMP or other messengers
nature - modulating
What is a type 2 muscarinic receptor involved in and how is it different?
involved in direct g gating where G beta gamma dissociates and activates a potassium channels known as a GIRK channel
In the absence of ACh what happens to the GIRK channel and what happens in the presence of Ach?
-you will see the GIRK channel us closes and the GIRK channel opens when ACh binds cause the G beta gamma subunit is not able to travel as far as the alpha but it opens it
What G complex is involved in the opening of GIRK channels?
G alpha i
-this GIRK channel opening causes slowing of the heart if you stimulate the vagus nerve this releases Ach on type II muscarinic receptors
How does serotonin close a potassium channel?
through a diffusible second messenger - via G alpha and PKS phosphorylates s type potassium channels - if you inject cAMP directly into the cells and they found that the potassium channel close and if you apply PKA they also close which causes depolarization making the neurons more excitable
What is retrograde transmission?
transcellular signaling which can occur from the postsynaptic neurons to the presynaptic neuron and between the postsynaptic cell
-can activate an enzyme and make a membrane permeable modulator and can diffuse and influence the presynaptic side of the synapse and neighboring synapses as well
If you have PLC and it cleaves DAGL what do you get?
2AG
If you have PLD and it cleaves N-arachidonyl PE what do you get?
anadamide
What are 2 AG and anadamide?
endocannabinoids which can bind to receptors activated by THC
Where are endocannabinoids released and what do they bind to and regulate?
postsynaptically and bind to presynaptic receptors to regulate NT release
At a glutamatergic synapse how does G alpha q from mGluR5 make 2AG and what does it do?
PLC cleaves DAGL - and makes 2AG and this diffuses to the presynaptic side and binds to endocannabinoid recepyros which is a metabotropic receptor associated with G alpha i which prevents teh actuvation of AC and PKA and this inhibits the presynaptic side and causes less AP - mGluR5 detects pathological amount of glutamate being released and prevents overactyvation of synapses which are apliteptogenic cause these mGluR5 receptors are in the outskirts of the synaptic cleft so if they detect glutamate there is excess glutamate
At what three cellular sites can the modulatory actions of second messengers occur?
- calcium channels phosphorylated making them stay open longer and cause more NT release
- potassium channels can be inhibited
- release machinery can be phosphorylated vesicles are released more easily
can also dephosphorylate and cause the opposite to happen
On the postsynaptic side what can metabotropic receptors do?
phosphorylate AMPARs and cause them to be open longer when glutamate binds
In the cell body what can metabotropic receptors do?
can cause voltage gated potassium channels to close so the depolarization is longer and harder to repolarize the cell
What ends the actions of protein kinases?
phosphoprotein phosphatases
When is a potassium channel open and closed?
open when phosphorylated and when not phosphorylated it is closed
What can an inhibitor protein do to a phosphatse?
it can bind to it and allow and elevated ability of PKA to phopsporyulate the potassim channels and leave it open
What can calcieurin do to a phosphatase?
when calcium is present it can cause dephosphorylation of inhibitor one and promote phosphatase to cause the channel to close
How can a single NT have a short term effect on an ion channel?
the NT binds to the G alpha s receptor and PKA phopshorylates the K channel and this is a fragile condition cause can undo phosphorylation easily
How can a single NT have a long term effect on an ion channel?
can have PKA make way to nucelus of neuron and phosphoylate regulaorty proteins which can bind to enhancer regions of a gene and the enhancer region can help a polymerase bind to a promoter region which can cause a greater number of potassium channels on the order of days so long term
What is a receptor tyrosine kinase?
dimers and are TM proteins and they have regions on the outside which have ligands that can bind to it and this causes the ligand to bind and then the subunit come togetehr and form a dimer and their subunits phopshoprylate each other which can now phosphorylate other proteins they can bind to PLC and make DAG and IP#
What are vascular endothelial growth factors receptors involved in and what is their ligand?
vasculogenesis
ligand - vascular endothelual growth factor
What are fibroblast growth factors receptors involved in and what is their ligand?
neural stemn cell proliferation, neurogenesis, axon growth
ligand - fibroblast growth factor
-are TKs
What are Trk receptors involved in and what is their ligand?
regulates synaptic strength and plasticity
ligand - neurotophins (NGF, BDNF)
What are Met receptors involved in and what is their ligand?
embryogenesis, synaptic maturation, autism risk gene
ligand - hepatocyte growth factor
What are Eph receptors involved in and what is their ligand?
synaptigenesis and two subunits come together and phosphorylate each other and other proteins which promote actin polymerization
ligand - ephrin A/B (homotypic)
