Lecture 3 Flashcards
What is the equilibrium potential?
The potential difference when a dynamic equilibrium has been reached.
The Nernst equation
E ion= RT/zF x ln [ion]ref/[ion]test
z=charge on ion
F=Faraday’s constant
If Vm does not equal E ion, what does this mean?
This means that the electrical force on the ion does not exactly balance the concentration-based force. The ion then experiences an electrochemical gradient.
If the membrane is freely permeable to only one ion species, we would expect…
the membrane potential (Vm) to equal E ion.
At the resting potential, why is the potassium permeability so much higher than sodium permeability?
Potassium leak channels
Which equation gives us a closer approximation of V rest than the Nernst equation?
The Goldman equation.
What is the proper name for the sodium pump?
Na+,K+-ATPase
What is the role of the sodium pump?
To maintain the concentration gradients for Na+ and K+ (this maintains the resting potential in the long term)
What is ouabain?
a sodium pump inhibitor
What are the effects of ouabain on the cell?
- a small rapid change in membrane potential (loss of electrogenic effect)
- very slow upwards drift of Vm as concentration gradients slowly dissipate
- membrane potential disappears
- cell begins to swell and may burst.
The membrane potential (Vm) always falls somewhere between E(K) and E(Na), what does its exact position depend on?
The relative permeabilities.
When is there a dynamic equilibrium?
When the flux due to the concentration gradient equals the flux due to the electrical potential gradient.
Why is the equilibrium potential reached so quickly?
Only a small number of ions need to cross the membrane.
Why does membrane potential remain constant in a resting animal cell?
- A large inwards electrochemical gradient for Na+ is coupled with a low permeability.
- A small outwards electrochemical gradient for K+ is coupled with a high permeability.
RESULT= the inwards Na+ current is equal to the outwards K+ current.
