Ion selectivity and gating

Question 1

what do you call disease of ion channels?

Answer 1

channelopothies

Question 2

what’s a pore?

Answer 2

• water filled hole
• always open
• water/ion/molecules travel through by osmosis/ diffusion

Question 3

what’s an ion-selective channel?

Answer 3

• ion-only gated - has a sensor to regulate

- natural state is closed- something happens to open it

Question 4

what does each transmembrane spanning region (TM) consist of?

Answer 4

a hydrophobic a-helix (inside membrane)

Question 5

during what process do proteins weave through cell membrane?

Answer 5

protein translation (whilst protein is still being synthesised)

Question 6

what’s the basic structure of Na+ ion channels?

Answer 6

24 TMs
looks like 4 TMs- pseudotetramer
main part is a-region

Question 7

what’s the basic structure of K+ ion channels?

Answer 7

tetramer- 4 protein subunits - with 2TM regions per subunit
a-subunit
pore forming P-loop regions and selectivity filter

Question 8

which is the simplest type of ion channel?

Answer 8

K+

Question 9

what are the 2 conformational states of ion channels?

Answer 9

open or closed

Question 10

what is the name for the transition between open and closed ion channels?

Answer 10

gating

Question 11

when an ion channel is at rest, what state is it in?

Answer 11

closed

Question 12

can an ion channel flutter between being open and closed?

Answer 12

yes

Question 13

what’s the first mode of ion channel activation?

Answer 13

twisting, tilting, bending

Question 14

what 5 events can trigger ion channel activation/opening?

Answer 14

ligand binding
intracellular ligand binding
intracellular modification
change in membrane voltage
mechanical distortion

Question 15

what important channel shows an inactivation process?

Answer 15

Na+

Question 16

what are the 2 mechanisms of ion channel inactivation

Answer 16

localised and particle

Question 17

what’s localised inactivation?

Answer 17

small regions in pore come into position and block off pore

Question 18

what’s the alternative name for localized inactivation?

Answer 18

C-type gating

Question 19

what’s particle inactivation?

Answer 19

ball and chain mechanism

Question 20

what’s the alternative name for particle inactivation?

Answer 20

N- type gating

Question 21

which ion do cell membranes have the highest permeability to?

Answer 21

K+

Question 22

what could be the sole determinant of membrane potential?

Answer 22

K+

Question 23

do K+ channels show absolute selectivity for K+?

Answer 23

no- have a low selectivity for Na+ (100 fold) and even lower for Ca2+ (another 100 fold)

Question 24

does removing a specific ion from intracellular fluid stop the ion channel conducting charge?

Answer 24

no- still support ion flow from other ions

Question 25

what are selectivity filters controlled by?

Answer 25

AAs with different charges depending on ion selectivity

Question 26

does RMP stay the same or vary between different types of cell?

Answer 26

varies

Question 27

are [K+]i and [K+]o constant between different cell types?

Answer 27

yes - but RMP still differs

Question 28

what 2 potassium channels do different cell membranes contain?

Answer 28

Kir and K2p

Question 29

what do both Kir and K2p have in their selectivity filters?

Answer 29

the same TVGYG sequence

Question 30

is RMP specifically related to the number of potassium channels?

Answer 30

no

Question 31

what then causes variation in RMP?

Answer 31

the selectivity filters of K+ ion channels e.g. less TVGYG, less potassium selective