Question

we talked about V_revfor the ACh-gated channel at the frog neuromuscular junction. We said that Na⁺and K⁺pass through this channel with equal permeabilities. We looked at how the V_revwas determined from the equilibrium potentials of the ions involved. As you know well, Eion is calculated from the concentrations of the ion inside and outside the cell, usinf the Nernst equation.  If the V_revyou predict is the same as the V_revyou measure experimentally, then you are probably correct in assuming the relevant ions and their relative conductance’s. But to really know which ions are involved, you can test the effect of changing ionic concentrations to change V_revin a predictable way. So, let's see what happens to V_revwhen an ion's concentration in the saline bathing the muscle is changed.

Given the following concentrations of Ions:

            [Na+]_out= 440mM

            [K+]_out= 20mM

            [Na+]_in= 50mM

            [K+]_in= 400mM

a.(3pts)What is V_rev, assuming equal permeabilities of the two ions?

                                    

b.(3pts) Now: what would you predict V_revwould be if increased [K⁺]_out10X, so it is now 200mM?

                                    

Answer 1