3 - Action Potentials I Flashcards
What affects sensitivity of membrane bound ion channels?
Physical shape and chemical properties
Gated membrane-bound channels may open/close depending on…
- mempot
- binding of a ligand to channel
Aquaporins are specialised channels that allow what to cross membrane?
Water
T/F at equilibrium, there’s absolutely no ion flow at all
False - no net flow but ion movement still occurs
Ions move towards…
Opposite charges depending on electrical field across membrane and open channels
Nernst equation predicts…
Mempot at equilibrium if membrane is only permeable to a single ion
What do you need to know for Nernst?
- Ionic concentrations (inside and outside cell)
2. Ionic charge (eg: +1 for Na+)
Equilibrium potential is independent of what?
Permeability and ionic conduction
What will mempot move towards if membrane only permeable to one ion?
That ion’s equilibrium potential
What equation do we use if membrane permeable to multiple ions?
GHK
What do you need to know for GHK?
- Internal and external concentration of each ion
2. Membrane permeability for each ion
At rest, what is the membrane’s permeability?
Weakly permeable to Na+ and quite permeable to K+
What is Resting Membrane Potential?
-65mV -> inside cell negative relative to outside
Does the Na/K-ATPase pump transport passively?
No - actively
What ion does the Na/K-ATPase pump push out of cell?
Pushes Na+ out and K+ in
How many ions does Na/K-ATPase pump transport?
For every 3 Na+ pumped out of cell, 2 K+ are pumped in
All K channels have how many subunits?
4 subunits with pore loops that regulate permeability
What are the 4 types of potassium channels?
- Two pore domain potassium channels (K2p)
- Voltage gated potassium channels
- Calcium-activated potassium channels
- Inward-rectifying potassium channels
K2p channels
- contain 2 pore loop domains which are usually open, contributing to ongoing K+ leak
- helps set RMP
Kv channels
- start opening when mempot >RMP
When do Nav channels open?
When membrane depolarises
At -65mV, are Nav channels open or closed?
Closed
At -40mV, are Nav channels open or closed?
Open for about 1ms, allowing Na influx
When do Nav channels inactivate?
When pore blocked by globular portion of protein
When do Nav channels reactivate (but still remain closed)?
When mempot reaches -65mV
What does textrodotoxin do?
Blocks one class of Nav channel so depolarisation can’t occur
You remain conscious but lose ability to generate APs in peripheral nerves
Describe how selectivity and gating occur in Na+ and K+ channels
Pore loops act as a physical filter (due to their close proximity)
Charged domains on amino acid residues act as a chemical filter
