Answer :
Tthe equilibrium potential for Ca²⁺ with extracellular Ca²⁺ concentration of 2.5 mM and cytosolic concentration of 100 nM is D. 135.2 mV.
The Nernst Equation is used to calculate the equilibrium potential for a specific ion based on the concentration of that ion inside and outside the cell. The simplified form of the Nernst Equation for an ion with charge z is:
E_ion = (61/z) * log([ion]_out/[ion]_in)
For Ca²⁺ (which has a charge of +2), considering the given extracellular concentration ([Ca²⁺]_out) of 2.5 mM and the cytosolic concentration ([Ca²⁺]_in) of 100 nM (which is equal to 0.0001 mM), we can substitute these numbers into the equation:
E_Ca²⁺ = (61/2) * log(2.5/0.0001)
Solve the logarithm and the calculation as follows:
- log(2.5/0.0001) = log(25000) ≈ 4.3979
- E_Ca²⁺ = (61/2) * 4.3979 ≈ 135.2 mV
Therefore, the correct option is d. 135.2 mV.
