L6 - ion channels Flashcards
what are the basic properties of ion channels?
- Gated (open and close depending on circumstances)
- selective permeability
- contain an aq pore
- have TMDs
structural requirements of an ion channel
a pore
a selectivity filter
a sensor ( eg voltage centre)
one or more gates
how many subunits does the nicotinic ACh receptor like ion channel have
5 (each with 4 TMDs)
how many a subunits does the NAChR always have?
2
how many TMDs does the NAChR channel have
which one contributes to the pore
4
2nd TMD of each subunit come together to line the pore
how many ACh (or ligands) need to bind to the NAChR channel and where do they bind
2x ACh bind to the alpha subunit
how many subunits does the VG Na channel have?
one large subunit
where are the C and N terminal of the VG Na channel located
intracellular
describe structure of the VG Na channel
TMDs and pore
4 repeating sections of 6 TMDs
the 4th TMD of each domain (6 in total) is the voltage sensor
there is a P loop between TMDs 5&6 of each domain which form the pore
what is the voltage sensor on the VG Na channel? and how does it work
the 4th TMD on each of the 6 domains
it contains charged AAs which move in response to voltage changes which can open the channel
what are subunits?
individual proteins which may have several TMDs
so the Ca and K channels are formed of many separate proteins whereas the Na channel is one single protein
how many subunits does the VG K channel have
4
how many TMDs does each of the subunits of the VG K channel have
and which one contributes to the
- pore
- voltage sensor
6
P loop contributes to pore
TMD 4 is the voltage sensor
what is the equilibrium potential (E) of K
-90mV
what is the equilibrium potential (E) of Na
+60mV
what is the equilibrium potential (E) of Cl
-70mV
what is the equilibrium potential (E) of Ca
+130mV
define electrochemical driving force
voltage that pushes the ions through the channel
the difference between the membrane potential and the equilibrium potential for that ion
Vm - E(ion)
what does a negative Em / Vm (both mean membrane potential) mean
inside the cell is more negative than the outside
at a Vm of -60mV, what is the electrochemical driving force for K
(-60) - (-90) = +30
what does it mean if the electrochemical driving force is
+
-
if its + ions flow out of cell
if its - ions flow into cell
what is the threshold for opening of VGCCs
-30mV
what is the reversal potential?
the membrane potential at which the flow of K+ out and Na+ in cancel eachother out
what would the reversal potential of a non selective Na and K channel be if t was equally permeable to both?
half way between the E(Na) and E(K)
-15mV
what is the usual reversal potential for non selective Na K channels and why is this the value
approximately 0mV
channel is slightly more permeable to Na than K
what is the threshold for opening of VG Na channels
-55mV (same as AP threshold)
what are the 3 ways ion channels can be classified based on their physiological properties
- Gating mechanism
eg voltage gated, ligand gated, temperature gated, [Ca]/[ATP] gated - ion selectivity
eg Na channel, non-selective cation channel - kinetics
eg fact activating, slowly inactivating, transient
what other ways can channels be classified
- based on their pharmacology
eg what channels are blocked/ opened by certain drugs - based on their structure
eg sodium channel, K channel, nAChR, P2Y channels etc
