8.3.P7

The Nernst Potential is important to understanding how electrostatic charges distribute in cells and tissue. One example we have studied is a model cell with a high 10mM concentration of NaCl on the outside and a small 40μM concentration of NaCl on the inside of the cell. Being a model, it is very simple and only contains Na channels. A physics student claims that the Nernst potential of Cl in this case would not be defined since there is no membrane channel present for Cl. A biology student on the other hand says that the Nernst potential is defined for any concentration difference, whether or not a channel is present. Discuss both viewpoints and suggest why each approach might be relevant in different contexts. Note: This is an essay question. Your answer will be judged not solely on its correctness, but for its depth, coherence, and clarity.

Joe Redish 5/2/13