Lecture 2 - Presynaptic events & Postsynaptic events

Question 1

What are some voltage-gated ion channels?

Answer 1

Kv
Nav
Cav
Cl

Question 2

How many separate subunits form the pore of a voltage-gated potassium channel?

Answer 2

4 separate subunits form the pore of a voltage-gated potassium channel

Question 3

The 4 domains of the mammalian sodium and calcium channels are linked
and encoded by a ______ ____

The main pore-forming subunit is the site where ____ or _____ bind

Answer 3

The 4 domains of the mammalian sodium and calcium channels are linked
and encoded by a single gene

The main pore-forming subunit is the site where drugs or toxins bind

Question 4

How does the sodium channel select Na+ and exclude K+?

Answer 4

Ion-water complex of Na+ fits in the size of the sodium channel selectivity filter but the size of the partially hydrated K+ ion does not.

Question 5

What are some examples of gating mechanisms?

Answer 5

•voltage
•ligands, eg. neurotransmitters, odorants
•cAMP, cGMP, ATP
•pH
•heat, cold, acid
•stretch (mechanosensitive)
•Ca2+, Na+

Question 6

What are the 3 modes of the patch clamp method?

Answer 6

1. Whole-cell mode
2. Inside-out patch mode
3. Outside-out patch mode

(and cell-attached recording)

Question 7

What is an inward or outward current?

Answer 7

Inward current (negative) - due to movement of positive ions into cell, e.g., Na+
Outward current (positive) - due to movement of positive ions out of the cell, e.g., K+

Question 8

What is a current clamp for?

Answer 8

Measure voltage change

Question 9

What are the various types of electrical recordings?

Answer 9

Receptor potential
Synaptic potential
Action potential

Question 10

______ bind to ion channels to inhibit their actions
______ used as pharmacological tools to distinguish ion channels

Answer 10

Toxins bind to ion channels to inhibit their actions
Toxins used as pharmacological tools to distinguish ion channels

Question 11

How does slowing of the closure of Na+ inactivation gate (by a toxin) affect the action potential?

Answer 11

The persistent Na+ current prolongs the action potential

Question 12

__________: Conduction of K+ ions through ____ of potassium channel
Ion shifts link to ______ and ____ of ions
Ion shifts within pore, no ______ or ____ of ions

Answer 12

Permeation: Conduction of K+ ions through pore of potassium channel
Ion shifts link to entry and exit of ions
Ion shifts within pore, no entry or exit of ions

Question 13

________-dependent Inactivation (VDI)
Mechanisms:
KV channels: ____ & _____
NaV channels: _____ and ___
CaV channels: not fully understood (likely _____ & ___); -also undergo ____-dependent Inactivation (CDI)

Answer 13

Voltage-dependent Inactivation (VDI)
Mechanisms:
KV channels: ball & chain
NaV channels: hinge and lid
CaV channels: not fully understood (likely hinge & lid); -also undergo Ca2+-dependent Inactivation (CDI)

Question 14

What is chemogenetics?

Answer 14

Mutagenising receptors to change sensitivity to certain small molecules

Depolarise and activate or
hyperpolarise and inhibit

Question 15

What is optogenetics?

Answer 15

Controlling the activity of neurons or other cell types using light

Question 16

How did Acetylcholine become the first identified neurotransmitter?

Answer 16

Square wave (positive current) and ACh pipet (positively charged Ach out of micropipet) both resulted in similar end plate potential (EPP) waveforms from motor axon

Question 17

_______ release: release of neurotransmitters in _______ packets

Answer 17

Quantal release: release of neurotransmitters in discrete packets

Question 18

How long does it take for arrival of action potential to response to neurotrasmitter release?

Answer 18

150μs:

90μs to open voltage-gated calcium channel –> Ca2+ influx
60μs for Ca2+ to trigger vesicle fusion, for neurotransmitter to diffuse across synaptic cleft and act on postsynaptic cells

Question 19

Neurotransmitter endocytosis is very highly regulated. What is the mechanism?

Answer 19

SNARE comes together to clamp into a closed formation to bring calcium channel close to synaptic vesicle
Calcium going to calcium channel will evoke fusion of vesicle and release of neurotransmitter

Question 20

It is important that transmitter release is transient & neurotransmitters are efficiently cleared from the synaptic cleft. How does this occur?

Answer 20

Neurotransmitters recycled into cytosol are refilled into new or recycled synaptic vesicles via vesicular neurotransmitter transporters. Energy for the symport transport of neurotransmitters into the SV is derived from transporting protons (H+) in the opposite direction.

Acetylcholine: degraded by acetylcholinesterase while Ach is diffusing across the cleft
Most neurotransmitters: recycling of excess neurotransmitters at the cleft by:
1. reuptake into presynaptic cytosol via plasma membrane neurotransmitter transporter
2. reuptake via glia plasma membrane neurotransmitter transporter

Question 21

Recycling of synaptic vesicle by endocytosis is important to maintain continual synaptic transmission. How does this occur?

Answer 21

Two means:
Kiss-and-run: SV reform after transient fusion (with cell membrane) with limited release of neurotransmitters
Clathrin-mediated endocytosis: SV membrane fuses fully with plasma membrane and is recycled or retrieved

Question 22

What is the suffix -ergic used for?

Answer 22

Synapses that use the neurotransmitter (found before the suffix)

Question 23

What are the criteria needed for a substance to be classified as a classical neurotransmitter?

Answer 23

1. Must be SYNTHESISED AND RELEASED from a neuron;
2. Release should be in a chemically or pharmacologically IDENTIFIABLE
   form;
3. Putative neurotransmitter, when APPLIED EXOGENOUSLY, should have same effect as the stimulation of neuron that synthesizes the neurotransmitter;
4. The effect of neurotransmitter should be BLOCKED by an antagonist;
5. There should be a mechanism to TERMINATE the action of the neurotransmitter or removal from its site of action;

Question 24

What are the types of classical neurotransmitters?

Answer 24

Amino acids: small organic molecules - vesicles
e.g., glutamate, glycine, GABA (gamma-aminobutyric acid)

Amine: small organic molecules - vesicles
e.g., dopamine, acetylcholine, histamine, epinephrine, norepinephrine, serotonin

Peptides: short amino acid chains (proteins) - secretory granules
e.g., dynorphin, enkephalins

Question 25

What is the purpose of scaffold proteins?

Answer 25

A scaffold network stabilizes neurotransmitter receptors at synaptic cleft appose to active zone and presynaptic release machinery; brings enzyme such as CaMKII close to upstream activator

Question 26

What is “Shunting”?

Answer 26

When an excitatory postsynaptic potential and an inhibitory postsynaptic potential are occurring close to each other on a dendrite, or are both on the soma of the cell

When GABA receptor is activated, it neutralises the excitatory effect of AMPA receptors.

Question 27

How does termination of GPCR signaling occur?

Answer 27

• GPCR is deactivated when ligand dissociates
• Gα-GTP is deactivated by intrinsic GTPase activity
• Gβγ is deactivated by re-association with Gα-GDP
• cAMP is metabolized into AMP by phosphodiesterase
• Catalytic units of PKA re-associate with regulatory subunits and become inactive
• Protein phosphatases remove phosphate from phosphorylated proteins