ionotropic receptors

Question 1

What are the main differences between ionotropic and metabotropic receptors?

Answer 1

Ionotropic receptors contain a ligand binding site and ion channel, while metabotropic receptors do not have ion channels and affect nearby ion channels via second messengers, most commonly via G-proteins.

Question 2

What is the time frame for postsynaptic effects mediated by ionotropic receptors?

Answer 2

1-2 ms post action potential, short lasting (<1 ms)

Question 3

Name some ligands that bind to ionotropic receptors.

Answer 3

• Ach
• Glutamate
• GABA
• Serotonin
• Glycine
• Drugs: nicotine (nAChRs), muscarine (mAChRs)

Question 4

What are the three superfamilies of ionotropic receptors?

Answer 4

• Cys-loop receptors
• Ionotropic glutamate receptors
• ATP-gated receptors

Question 5

What is the structure of Cys-loop receptors?

Answer 5

Pentameric, typically alpha-alpha-beta-gamma-delta with 4 transmembrane domains and 2 ligand binding sites.

Question 6

How are AMPA receptors structured?

Answer 6

Tetrameric with 4 transmembrane domains each and 4 agonist binding sites.

Question 7

What is the structure of P2X receptors?

Answer 7

Trimeric with 2 transmembrane domains each and 3 ligand binding sites.

Question 8

How many genes encode the nicotinic acetylcholine receptor?

Answer 8

16

Question 9

What is the role of alternative splicing in AMPA receptor subunits?

Answer 9

Generates diversity by producing flip and flop isoforms, affecting receptor recovery from desensitization.

Question 10

What are the implications of RNA editing in GluA2 subunits?

Answer 10

Alters calcium permeability; unedited (Q) allows Ca²⁺ permeability, edited (R) is impermeable to Ca²⁺, protecting neurons from excitotoxicity.

Question 11

True or False: The majority of GluA2 subunits are edited in healthy neurons.

Answer 11

True

Question 12

What happens when ACh binds to the nicotinic ACh receptor?

Answer 12

Induces conformational changes, exposing (opening) the ion pore.

Question 13

Fill in the blank: Nicotinic ACh receptors are widely expressed in the _______ and _______.

Answer 13

[muscular system], [nervous system]

Question 14

What is the physiological role of nicotinic ACh receptors?

Answer 14

Mediate fast, excitatory synaptic transmission.

Question 15

What is desensitization of nicotinic ACh receptors?

Answer 15

An accumulation of receptors in an agonist-bound but non-conducting conformational state.

Question 16

What are the properties of AMPA receptors?

Answer 16

Permeable to Na+ and K+, generating excitatory postsynaptic potentials (EPSPs).

Question 17

What does the activation of NMDA receptors require?

Answer 17

Binding of glutamate and glycine, plus membrane depolarization to remove Mg²⁺ block.

Question 18

What is long-term potentiation (LTP)?

Answer 18

A cellular correlate of memory formation involving long-lasting enhancement in synapse transmission between two neurons.

Question 19

What is the role of calcium influx in LTP?

Answer 19

Activates protein kinases leading to the insertion of additional AMPA receptors into the membrane.

Question 20

What is long-term depression (LTD)?

Answer 20

A long decrease of synaptic function, typically induced by prolonged low-frequency synaptic stimulation.

Question 21

What pathological condition is associated with mutations in nicotinic ACh receptor subunits?

Answer 21

Autosomal dominant frontal lobe epilepsy.

Question 22

What is the effect of cigarette smoking on nicotinic ACh receptors?

Answer 22

Acts as an antidepressant through rapid AChR desensitization.

Question 23

What is the significance of the R/G site in AMPA receptors?

Answer 23

Involves replacement of an arginine (R) with a glycine (G) through RNA editing, affecting recovery from desensitization.