Question

 

Assume ionic concentrations in the nervous system of:

[K]_o = 4 mM

[K]_i= 155 mM

[Na]_o= 145 mM

[Na]_i= 12 mM

1. Use the Nernst equation to calculate the Equilibrium potential for potassium (E_K). Show all your calculations. (Assume RT / zF = 58 mV).

2. Would the membrane potential of a glial cell be the same as, or different from E_K?

Explain your answer .

3. What ratio of [K]_o : [K]_in will cause E_K in a glial cell to be exactly zero (0 mV)? Why?

Answer 1

E_,K= is the equilibrium potential for potassium

R =is the universal gas consatnt equal to 8.314joules ·K⁻¹·mol⁻¹

T= is the Absolute Temperature, measured in kelvin (= K = degrees Celsius + 273.15)

z =is the number of elementary charges of the ion in question involved in the reaction

F =is the faradays constant equal to 96,485Coulombs

[K⁺]_o = is the extracellular concentration of potassium,

[K⁺]_I = is the intracellular concentration of potassium

b)Glial cells are also differentiating and proliferating as development progresses in the brain.The addition of these glial cells increases the organism’s ability to regulate extracellular potassium. The drop in extracellular potassium can lead to a decrease in membrane potential .