Question

1a.If the concentration of Sodium on side A ofa membrane is 7 mM and the concentration of sodium on side B is 175 mM, what direction will sodium want to move? (1pt)

1. b. If in the situation above sodium is at equilibrium, what is sodium's contribution to the membrane potential? Which side of the membrane has the more positive charge on it? (show your calculations) (3pts)

Answer 1

1)a) Sodium will tend to move from region of higher concentration to the region of lower concentration.Since concentration of sodium is more on side B(175 mM) than side A(7 mM); so sodium ions will move from side B to side A.

b) Contribution of sodium to membrane potential is its Nerst potential.

Nerst potential = 61.5/z ( log(concentration outside/concentration inside))

z=1; concentration outside=175 mM; inside= 7 mM

Putting in the values; nerst potential=-86 mM

Since concentration of sodium is more on side B(outside) ; it is more positive.