BIOELECTRICITY Flashcards
How do you measure membrane potential?
Use of a glass electrode to penetrate a cell (much like the Patch Clamp method but with a smaller pipette)
What is determination of membrane potential dependent upon?
Unequal and selective distribution of ions, mainly sodium, potassium and anions.
What is the EC concentration of sodium?
150mM
What is the EC concentration of potassium?
5mM
What is the EC concentration of anions ?
0mM
What is the IC concentration of sodium?
15mM
What is the IC concentration of potassium?
150mM
What is the IC concentration of anions?
65mM
Resting membrane potential is approximately -70mV. How much of this is generated by the Na/K ATPase?
20%
How is the membrane potential set?
There is high IC potassium ions and low EC concentration therefore there is a concentration gradient for potassium ions to move out of the cell. The movement of potassium ions out of the cell means the intracellular environment becomes more negative, large trapped anions also contributing to this negativity. This creates a large chemical gradient for potassium ions to move back into the cell. When movement of ions inwards = movement of ions outwards you have reached equilibrium. This is occuring for many ions and this contributes to the membrane potential.
How do you calculate the equilibrium potential for a single ion?
Eion=
RT/zF . ln([ion]out/[ion]in)
Where: R = gas constant T = temperature (K) z = ion valence F = faradays constant
What is the relative permeability of sodium?
1
What is the relative permeability of potassium?
50-75
What is the relative permeability of anions?
0
What is the Goldman Equation used for?
To calculate the equilibrium potential taking multiple ions into account therefore a more accurate measure of membrane potential.
