Neuronal Cell Signalling Flashcards
what happens when the voltage gated calcium channels are activated?
- couples the action potential to the neurotransmitter
- NT binds and opens ligand gated ion channels
- mediate direct excitation or inhibition of postsynaptic cell
- NT interacts with G protein coupled receptors
- initiates intracellular signalling effects
what are GPCRs?
- not ion channels
- regulates voltage gated and ligand gated ion channels
what are the functions of GPCRs?
- Binds NTs, neuropeptides and hormones
- they bind and activate heterotrimeric G proteins that they’re associated with
- subunits initiate different events that lead to a change in the gating of ion channels
- trigger excitation/inhibition
- modulate excitability
what are GPCRs on the presynaptic membrane?
- VGCCs - couple AP to NT release
what are GPCRs on the postsynaptic membrane?
ligand gated and voltage gated ion channels
how are signalling events triggered?
by GPCR coupled receptors and Ca2+
how does receptor activation cause a conformational change in GPCR regulated ion channels?
- alpha unit exchanges GDP for GTP
- alpha subunits interact with and influence activity of an effector protein
- terminated by GTPase activity of alpha subunits
- alpha subunit reunites with beta gamma subunits
what are G alpha effectors?
enzymes that generate second messengers
what is PkA/camK?
voltage and ligand gated channels, vesicle proteins, transcription factors
what do G beta gamma interact with?
- directly interact with ion channels in the membane to alter the activity
- G alpha and G beta gamma have different effectors/targets
how do we test for second messenger v G beta gamme mediated effects?
- electrical isolation (in the patch pipette)
- physical separation
- can put compounds in the patch and won’t have access to the bathing medium
how is a NT in the bathing medium affecting an ion channel thats in a patch pipette?
- NT interacting with a receptor (GPCR)
- to initiate a signalling cascade
- allows generation of a diffusible messenger
- allowing Ca2+ channel to open for longer
how is PkA involved?
- phosphorylates voltage gated calcium channels
- alters their opening
how can a cell attached patch test for second messenger vs G beta gamma mediated effects?
giga-ohm seal prevents movement of NT between extracellular medium and solution in pipette
what have cell attached patch recordings been used to show?
- intracellular inject of cAMP (elicits the same effects as NT)
- PkA phosphorylates the channel to increase open probability and open time
how to examine G beta gamma?
- Detached membrane patch ‘inside out’
- Patch pipette pull pipette away and rupture the membrane
- Inside of cell is facing the bathing medium
- Have to use GTP to see any activity
- Depolarising pulse can see activity of K+ channels
- Put acetylcholine in the pipette interacts with a GPCR (Mescarinic Ach)
- As you pull the membrane away from the cell you lose channel activity
α subunit is using up the GTP hydrolyses
becomes GDP reassociates with β γ subunits
can restore reactivity with GTP in the solution - Proves there is a membrane delimited regulation
- Prove the importance of β γ by just using those subunits
what are beta gamma subunits?
- potassium channels (GIRKs)
- beta gamma can activate K+ channels and can inhibit Ca2+ channels
what can cannabinoids activate?
- activates K+ channel and inhibits
what happens when K+ channels are activated?
less excitable, modulation
how is there presynaptic inhibition?
decrease in NT release due to inhibition of VGCC and activation of K+ channels via Gi/o coupled receptors
how is there presynaptic facilitation?
- increase NT release due to activation of VGCC
how can you modulate postsynaptic receptors?
- changing the number of PS receptors
- trafficking and gating
- Ca2+ downstream of NMDA can activate CAM kinase II
- CAM kinase II and PkC mediation phosphorylation of postsynaptic AMPA receptors
- intracellular Ca2+ can increase in many ways
what are the features of Ca2+ signalling??
- regulated tightly
- glutamate binds to a receptor causing depolarisation and an influx of Ca2+
- IP3 interacts with receptors on ER and causes a release of Ca2+
how can ER release Ca2+ in a controlled and effective manner?
- also has a RyK receptor
- activated by Ca2+
- causes more Ca2+ release
what happens when the intrallelar store is emptied?
- calcium levels in the cell needs to go back down
- pumped out using plasma membrane ATPase
- exchanges Ca2+ for Na+ exchanger
- refills calcium stores, pumps back into stores through another ATPase (SERCA)
what happens when the neuron has a depletion of Ca2+?
- calcium stores can send a depletion signal to the plasma membrane allows calcium back in
what are some extracellular Ca2+ sources?
- SOC (store operated channels)
- LGC (NMDA receptor
- VGCC (postsynaptic L type voltage gated Ca2+ channels)
what are the intracellular Ca2+ release channels on the ER?
- IP3 receptors
- Ryanodine receptors
how do IP3 receptors work?
- activated by increased IP3 levels via Gq-cuopled metabotropic glutamate receptors
how do ryanodine receptors work?
activated by Ca2+ coming through NMDA receptor/VGCC causing Ca2+ increase –> induced Ca2+ release
what is Ca2+ removed?
- SERCA (sarcoplasmic endoplasmic reticulum Ca2+ ATPase, pumps Ca2+ back into the ER)
- PMCA (pumps Ca2+ out of the cell)
- NCX (Na+/Ca2+ exchanger)
what is the cyclic nucleotide gated channels?
direct opening of ion channels by second messengers
what do cGMP gated Na+ channels mediate?
changes in the activity of photoreceptor cells ‘ receptor potentials’
what is cGMP?
- gated by cyclic nucleotides eg cyclic AMP or cyclic GMP
- a photoreceptor
- change in membrane potential which causes a receptor potential
what are the basics of a cGMP photoreceptor?
- activation of GPCR (rodopsin)
- activates a G protein (transducin)
- activates effector molecule which decrease cGMP levels through a phosphodiesterase
what are transient receptor potential cation channels?
- TRP channels
- some TRP channels in sensory neurons are store operated channels, modulated by second messengers
what are the functions of TRPs?
olfaction vision touch pain - sense that the ER is empty
how does an odorant interact with a TRP?
- increase in IP3, intracellular Ca2+ increase
- sends a signal (STM1 mediated) to plasma membrane
- activates TRP channel to cause primary excitation of a sensory neuron
