Ion-channel Coupled Receptors

Question 1

Which types of cells are ICCR’s found?

Answer 1

Excitable cells ⚡️

Question 2

ICCR’s convert what type of signals?

Answer 2

Chemical and mechanical to electrical

Question 3

Upon ligand binding…

Answer 3

1. Conformational changes occur, leading to formation of channel/pore
2. Molecules such as Ions (like K and Na) pass through membrane in or out to propagate travelling signal

Question 4

What determines which ions pass the membrane?

Answer 4

The specific dimensions of the ion channel, the amino acids that line said channel, the associated receptor and the binding ligand

Question 5

What are ion-channel coupled receptors also known as?

Answer 5

Ligand-gated ion channels

Question 6

What usually binds to the receptors of these ICCR’s? Give examples of each

Answer 6

Neurotransmitters (acetylCholine) or peptide hormones (Growth hormone)

Oxytocin is both a neurotransmitter & peptide hormone that acts on ICCR’s

Question 7

What affect does the passage of ions have on the cell in question?

Answer 7

As ions carry charge, the electronic membrane potential can be altered through unequal distributions across the extracellular and Intracellular environments

Question 8

What is the usual ionic composition of the Intracellular and extracellular environments? And what do their differences create?

Answer 8

Na concentration greater outside than inside
K concentration greater inside than outside

This creates an electrochemical gradient, which upon channel opening, ions flow down to restore electrochemical equilibrium.

Question 9

What happens when the bound ligand detaches?

Answer 9

The ion pore closes and the refractory period begins, after which ion channel formation can occur once again

Question 10

Where are ICCR’s often found?

Answer 10

Mostly on synaptic structures of neurones and other excitable cells.

Question 11

Briefly detail the sequences of synaptic transmission

Answer 11

1. Presynaptic neuron is excited
2. Vesicles containing neurotransmitter are released into synaptic cleft
3. These bind ion-channel coupled receptors on surface of post-synaptic neuron causing ion channel opening
4. Ions flow in or out of post-synaptic neuron

Question 12

What occurs if the signal is excitatory or inhibitory?

Answer 12

Excitable : ion movement elevates potential of post-synaptic neuron
Inhibitory ✋: ion movement decreases potential of post-synaptic neuron

Question 13

What threshold must be achieved for the post-synaptic to relay signal the incoming signal?

Answer 13

The motherfucking ACTION POTENTIAL!!

Question 14

To where are ion-channel coupled receptors bound?

Answer 14

The membrane (insane in)

Question 15

What type of ICCR’s are found in high abundance on the plasma membrane (sarcolemma) of muscle fibres/cells, why so and what is the primary source of the binding ligand?

Answer 15

The receptors are called muscle-type nicotinic AcetylCholine receptors (AChRs). They bind AcetylCholine and cause muscle contraction. Found in high abundance at neuromuscular junctions between motor neurones (primary source of AcetylCholine) and muscle cells.

Question 16

What are the two types of nicotinic AChRs and what are they involved in?

Answer 16

1. Muscle-type nicotinic AChR
2. Neuronal nicotinic AChR
3. Located at neuromuscular junctions, muscle contraction
4. Located at synapses of neurons, found also in CNS and contribute to cognitive function, learning and memory

Question 17

What other type of receptor also binds AcetylCholine but is not an ICCR and how does it compare?!

Answer 17

Muscarinic AChR’s, are G-protein coupled receptors. Functionally distinct from Nicotinic receptor, it’s agonist is Muscarine not nicotine and works via slower secondary-messenger cascades.

Question 18

What drugs target these fast-response nicotinic AChRs?

Answer 18

Muscle relaxants

Question 19

What are the ion channels opened by Nicotinic AChRs defined as?

Answer 19

Cation channels as they permit the flow of the postive ions K+ and
Na+ at a rate of 15,000-30,000 ions each millisecond

Question 20

What specific cells have an abundance of ICCRs?

Answer 20

Neuronal cells, muscle cells and touch receptor cells (e.g. skin of finger pads)

Question 21

ICCRs partially span the membrane and are usually monomeric.

True or false?

Answer 21

False. They span the entire membrane and are usual multimeric.

Question 22

How is the receptor and it’s associated ion channel complex linked?

Answer 22

Covalently.

Question 23

Describe the steps of basic skeletal muscle contraction for the neurotransmitter AcetylCholine and an ionotropic pathway.

Answer 23

1. Action potential reaches terminus of pre-synaptic motor neurone
2. Voltage gated Ca2+ channels open causing influx into the neurone
3. Consequently AcetylCholine is released into the synaptic cleft
4. ACh binds nicotinic AChR’s on muscle cells plasma membrane causing localised an influx of Na+ and localised depolarisation from resting potential (-75 to -80) to action potential (-15 to 0)
5. The generated action potential spreads across membrane triggering the opening of voltage gated Na+ channels
6. Action Potential reaches T- tubules whereupon voltages gated calcium channels are opened causing an efflux of Ca2+ out of the sarcoplasmic reticulum and into the cytosine causing contraction of the muscle cell