Epithelial with the ability to transport NaCl is bathed in an isotonic salt solution with these values (in mM): 136 Na, 6 K, 140 Cl. The intracellular concentrations are: 45 Na, 100 K, 13 Cl.
The cell's resting potential is -63 mV and the temperature is 37 Celcius.
Which ions will passively diffuse over the membrane?
My attempt: I calculate the nernst potential of each ion and taking the first ion (Na) as an example I get that it's equilibrium is at 29 mV. So as there are more of these cations outside the cell and the membrane potential is negative, the ions will want to "reach" 29 mV by flowing INSIDE the cell (to increase the membrane potential). I think they will do this by diffusing into the cell? I'm not sure if I am attacking the problem correctly or if it's rather lunging at my abilities in transporters. The NaK transporter is active transport so maybe the do not diffuse at all?? However there are Na channels that can open...Which is passive diffusion..
Calculate the cation permeability Pna/Pk
I have no idea how to do this. I still need more constants in the Goldman equation (Pcl for example) before I could isolate even one of these.