NaV channels Flashcards
at what mV is the NaV closed
-65
at what mV is the NaV open
-40
how is it selective towards Na
only allows Na+ ions to pass
ex - K+ ions are too large
how does the channel open
by depolarisation
how long do they stay open for, and what happens once they close again
~1msec, and then they become inactive and cannot be opened again
what happens in response to a membrane depolarisation
they open rapidly from a resting state
what happens when depolarisation is maintained
the Na+ channels exit open state and enter inactivated state
define whole cell current
individual channels open at different times, so this is ever changing
R =
resting (closed) state (favoured by hyperpolarisation)
O =
open state (transiently favoured by depolarisatoon)
I =
inactivated state (favoured by maintained depolarisation)
how many gates do Na+ channels have within axons
2
what are the 2 gates within axons called
activation gate and inactivation gate
describe the events of an action potential in a cell at the Na+ channels
- at the resting membrane potential, the activation gate closes the channel
- depolarising stimulus arrives at the channel and opens the channel
- with activation gate open, Na+ enters the cell
- inactivation gate closes and Na+ entry stops due to hyperpolarisation
- during repolarization caused by K+ leaving the cell, the 2 gates reset to their original positions
what is activation of NaV channels dependant on
voltage
more depolarisation =
more sodium influx
the amount of Na+ current (i.e. proportional to number of open channels) is dependant on
the magnitude of the depolarisation
what is inactivation of NaV channels dependant on
voltage
the process of inactivation determines …
the number of Na+ channels avaliable to open at any given membrane potential
how many beta subunits are there
4 (beta1-beta4)
what is the difference between all the beta subunits
they have similar structures but are seperate proteins
what to beta protein subunits modulate
channel gating, allowing rapid activation and inactivation
what is a mutation in the beta1 subunit associated with
epileptic seizures
what do immunoglobulin domains thought do do
bind extracellular proteins and be important determinants of channel localisation in cells
what does the extracellular domain of both beta proteins possess
an immunoglobulin-like fold