Question

In a two-compartment model of a cell with a K - and Cl --permeable membrane and a 10-fold excess of KCl in the inside compartment, how would the membrane potential change if all the beginning KCl solutions (including inside and outside) were replaced by NaCl

Answer 1

Answer:

When the solutions (including inside and outside) were replaced by NaCl, the membrane potential changes from a negative value of -60 mV to a positive value of + 60 mV.

Explanation:

According to the Nernst equation the potential of the membrane for a two-compartment model of a cell for positive gradient of K⁺ ions is V = - 60 mVlogK'/K where K' = inside concentration of K⁺ ions and K = outside concentration of K⁺ ions. For a 10 fold excess of KCl in the inside compartment, K'/K = 10. So,

V = - 60 mVlogK'/K = - 60 mVlog10 = -60 mV.

For a negative gradient of Na ions is V = + 60 mVlogK'/K where K' = inside concentration of Na⁺ ions and K = outside concentration of Na⁺ ions. (Since the cell is selectively permeable to Na⁺ ions. So, Na ions to not flow out but in.)For a 10 fold excess of NaCl in the inside compartment, K'/K = 10. So,

V = + 60 mVlogK'/K = + 60 mVlog10 = +60 mV.

So, when the solutions (including inside and outside) were replaced by NaCl, the membrane potential changes from a negative value of -60 mV to a positive value of + 60 mV.