Ion selectivity and gating Flashcards
what do you call disease of ion channels?
channelopothies
what’s a pore?
- water filled hole
- always open
- water/ion/molecules travel through by osmosis/ diffusion
what’s an ion-selective channel?
- ion-only gated - has a sensor to regulate
- natural state is closed- something happens to open it
what does each transmembrane spanning region (TM) consist of?
a hydrophobic a-helix (inside membrane)
during what process do proteins weave through cell membrane?
protein translation (whilst protein is still being synthesised)
what’s the basic structure of Na+ ion channels?
24 TMs
looks like 4 TMs- pseudotetramer
main part is a-region
what’s the basic structure of K+ ion channels?
tetramer- 4 protein subunits - with 2TM regions per subunit
a-subunit
pore forming P-loop regions and selectivity filter
which is the simplest type of ion channel?
K+
what are the 2 conformational states of ion channels?
open or closed
what is the name for the transition between open and closed ion channels?
gating
when an ion channel is at rest, what state is it in?
closed
can an ion channel flutter between being open and closed?
yes
what’s the first mode of ion channel activation?
twisting, tilting, bending
what 5 events can trigger ion channel activation/opening?
ligand binding intracellular ligand binding intracellular modification change in membrane voltage mechanical distortion
what important channel shows an inactivation process?
Na+
what are the 2 mechanisms of ion channel inactivation
localised and particle
what’s localised inactivation?
small regions in pore come into position and block off pore
what’s the alternative name for localized inactivation?
C-type gating
what’s particle inactivation?
ball and chain mechanism
what’s the alternative name for particle inactivation?
N- type gating
which ion do cell membranes have the highest permeability to?
K+
what could be the sole determinant of membrane potential?
K+
do K+ channels show absolute selectivity for K+?
no- have a low selectivity for Na+ (100 fold) and even lower for Ca2+ (another 100 fold)
does removing a specific ion from intracellular fluid stop the ion channel conducting charge?
no- still support ion flow from other ions
what are selectivity filters controlled by?
AAs with different charges depending on ion selectivity
does RMP stay the same or vary between different types of cell?
varies
are [K+]i and [K+]o constant between different cell types?
yes - but RMP still differs
what 2 potassium channels do different cell membranes contain?
Kir and K2p
what do both Kir and K2p have in their selectivity filters?
the same TVGYG sequence
is RMP specifically related to the number of potassium channels?
no
what then causes variation in RMP?
the selectivity filters of K+ ion channels e.g. less TVGYG, less potassium selective
