Lecture 3

Question 1

3 main types of ion channel

Answer 1

Voltage gated ion channel
Neurotransmitter ion channel
Secondary messenger ion channel

Question 2

Voltage gated ion channels

Answer 2

1. Na+ ion channels open, allowing for Na+ influx, more positive membrane voltage
2. K+ ion channels open, efflux causes more negative membrane voltage
3. Ca2+ ion channels open, allowing for influx, increases cytosolic calcium ion levels

Question 3

Neurotransmitter gated channels

Answer 3

Gating of these channels is via extracellular substances

Question 4

Examples of neurotransmitters which open NGC

Answer 4

acetyl choline and glutamate both select for cations in action potentials
GABA and glycine both select for Cl- ehich inhibits APs

Question 5

Second messenger-gated channels

Answer 5

Gating of channels is via a cytosolic second messenger.

Question 6

Example of Second messenger-gated channels

Answer 6

Cyclic nucleotide-gated channels (CNGCs)
Cation selective and gated by cAMP or cGMP

Question 7

Retinal vs olfactory

Answer 7

Retinal: Light into action potentials

Olfactory: Chemicals (smells) into action potentials

Question 8

Second messenger-gated channels

Answer 8

Inositol 1, 4, 5 triphosphate (IP3) receptors:
These are Ca2+-selective and release Ca2+ from the ER to elevate cytosolic Ca2+ during cell signalling events.

Question 9

Structure of voltage gated ion channels

Answer 9

6 TMS domains (S1-S6)
Pore domain
Voltage senser composed of many positively charged a.a. residues
Long ‘N’ terminus forms ‘ball and chain’ arrangement involved in inactivation

Question 10

What forms selectivity filter and pore region?

Answer 10

P-loop

Question 11

Conserved amino acids in P-domain

Answer 11

K+ channels - GYG - Glycine, tyrosine, glycine
Ca2+ channels - E - glutamate
Na+ channels - DEKA - aspartate, glutamate, lysine, alanine

Question 12

Where is voltage sensing achieved and with what sequence?

Answer 12

S4
XXRXXRXXRXXRXXRXXK

Sliding helix model:
Change in voltage forces the arginine residues to move up through the membrane which in turn forces a conformational change which opens the gate

Question 13

Inactivation of voltage-gated channels: the ball and chain model

Answer 13

K+ channel with N-terminus amino acid residues removed (mutant) - Constant activity

Mutated K+ channel with N terminus polypeptide added back - Slower decrease in ion channel activity

K+ channel inactivation (wild-type)