Question

A model cell contains the intracellular ions Na+, K+, Cl-, and An- (impermeant

anions) and the extracellular ions Na+, K+, and Cl-. The concentration

(activities) of [Na+]o=125 mmol l-1, [K+]o = 5 mmol l-1, whereas [An-]i = 123

mmol l-1, [K+]i= 112 mmol l-1. Assume the membrane is permeable to Na+, K+,

and Cl-. [ The subscripts i and o refer to inside and outside, respectively]. The

relative permeabilities for the ions are pNa/pK=0.02, pCl/pK=0.1

a) What are the values of [Cl-]o, [Na+]i, and [Cl-]i, for this cell to be in

equilibrium? (take into account both electrical and osmotic

considerations).

b) What are the equilibrium potentials of all the permeant ions?

c) What is the resting membrane potential (Em) of the cell?

3. Suppose the cell in question 2 is initially at the calculated resting potential. A

stimulus is suddenly applied to the cell and causes the membrane to become

very permeable to Na+ ions. Explain how Na+ moves initially, and what

happens to the membrane potential (immediately after). Also explain the

resulting movements of Cl- and K+ ions in the short run.

Answer 1

Que:- 2 (b) Equilibrium potential is the membrane potential where the net flow through any open channel is zero it is measured at that time when chemical and electrical forces balance each other and can be calculated using Nernst equation.

(c) Resting Potential of a cell is the voltage difference across the cell membrane when the cell is at rest. It is the product of the distribution of charged particles