I am still new in learning this method at present.
If what I understand is right, to test the relative ion permeability of one type of ion channels, we initially use the Goldman equation. We set the permeability of one ion (like K+) as 1 normalizing other ions permeability to it.
Say like we are tesitng relative permeability of [Na+], technically we need values of [Na+]i, [Na+]o, [K+]o, [K+]i and Vm to apply to the equation and calculate the value of Pna/Pk.
Quesiton is: should the Vm here resting membrane potential (current=0)? In my opinion the Vm should be the balanced membrane potential when there are only two ions Na+ and K+ in the solution of both side. I am not sure which is right.