How would I find the reversal potential for conductance

[madbeemer]

I know the following
ion/inside cell/outside cell
Cl- 5mM 150 mM
K+ 130mM 5mM
Na+ 20mM 140mM
Ca2+ 10^-4mM 2mM

How would I find the reversal potential for conductance equally permeable to sodium and potassium?
How do I find the reversal potential for a conductance equally permeable to sodium, potassium, and chlorine?

 

[madbeemer]

Do you use nernst? lol Help please. Not sure how to go about this.

 

[kyle8921]

To find the reversal potential for conductance, you will need to use the Goldman-Hodgkin-Katz equation. This equation takes into account the relative permeability and concentrations of each ion to determine the overall reversal potential. It is given by:

Erev = (RT/zF) ln((PNa+[Na+]o + PK+[K+]o + PCl-[Cl-]o)/(PNa+[Na+]i + PK+[K+]i + PCl-[Cl-]i))

where R is the gas constant, T is the temperature in Kelvin, z is the valence of the ion, F is the Faraday constant, P is the relative permeability of the ion, and [ion]o and [ion]i are the concentrations of the ion outside and inside the cell, respectively.

For the first question, where the conductance is equally permeable to sodium and potassium, you will need to set PNa and PK to be equal in the equation. This will simplify the equation to:

Erev = (RT/zF) ln((P+[Na+]o + P+[K+]o)/(P+[Na+]i + P+[K+]i))

where P+ is the permeability of both sodium and potassium. You can then plug in the given concentrations for each ion and solve for Erev.

For the second question, where the conductance is equally permeable to sodium, potassium, and chlorine, you will need to set PNa, PK, and PCl to be equal in the equation. This will simplify the equation to:

Erev = (RT/zF) ln((P+[Na+]o + P+[K+]o + P-[Cl-]o)/(P+[Na+]i + P+[K+]i + P-[Cl-]i))

where P+ is the permeability of sodium and potassium, and P- is the permeability of chlorine. You can then plug in the given concentrations for each ion and solve for Erev.

It is important to note that the Goldman-Hodgkin-Katz equation assumes that the membrane is only permeable to these three ions and that there are no other factors affecting the membrane potential. Additionally, the equation assumes that the membrane is at equilibrium, meaning that there is no net movement of ions across the membrane. If these assumptions do not hold, the calculated reversal potential may not accurately reflect the true potential.