Equilibrium potential for an ion is calculated using-
Ans. is 'b' i.e., Nernst equation Nernst equation o When two ionic solutions (ions) A and B of different concentration (CA and CB) of an ion separated by a permeable membrane, the ions tend to diffuse along their concentration gradient. Since ions are charged particles their diffusion can be stopped by an appropriate electrical potential (E) applied across the membrane o The magnitude and polarity of the potential (equilibrium potential) that must be applied to side A of the membrane for stopping the diffusion of ions (EA) is given by Nernst equation, i.e., the equilibrium potential for an ion is calculated by Nernst equation. o For example, if solution A contains an ion with a negative charge in more concentration than the concentration of the same ion in solution B, the ion will diffuse from A to B along the concentration gradient. If an electric gradient is created in opposite direction, the magnitude of the potential that completely counteracts this diffusion (from A to B) is called equilibrium potential. # EMF = +- 61 CA/CB # Where EMF is electromotive force or equilibrium potential in millivolts. o For example, the application of Nernst equation to the concentration of K+ in ICF (150 mEq/L) and in ECF (5 mEq/L) gives a value of - 90 mV. This is called the Nernst potential for K+ (EK). EK = -61 + ------ +1 log 150 ------ 5 -90 mV Ion Concentration (meq/L) Nemst potential or Equilibrium potential (mV) Inside cell (ICF) Outside cell (ECF) Na+ K + C1-- 15[?]0 150[?]0 9[?]0 150[?]0 5[?]5 125[?]0 + 60 -90 -70 o Resting membrane potential is -70 mV. So, resting membrane potential has a value similar to equilibrium potential or isoelectric potential of Cl~ .
Gibbs-Donnan equation
Nernst equation
Goldman equation
Fick's law
Membrane Potentials and Action Potentials