Question

If the intracellular concentration of Ca2+ was 10mEq/L and the extracellular was 170mEq/L, the equilibrium potential would be

A. -37.9mV.
B. -71.8mV.
C. +35.9mV.
D. +37.5mV.

Answer 1

By applying the Nernst equation and using the given intracellular and extracellular concentrations for Ca2+, the equilibrium potential for Ca2+ can be calculated as approximately +37.5mV, making D. +37.5mV the correct answer.

Step-by-step explanation:

To determine the equilibrium potential for calcium ions (Ca2+) across a cell membrane, we can apply the Nernst equation. The Nernst equation calculates the potential difference (voltage) across the membrane that would be required to balance the concentration gradients of a particular ion.

1. Identify the concentrations of Ca2+ inside and outside the cell: intracellular = 10mEq/L, extracellular = 170mEq/L.
2. Convert concentrations from mEq/L to mol/L (since 1mEq of Ca2+ = 0.5 mmol/L due to its +2 charge): intracellular = 0.01*0.5 = 0.005 mol/L, extracellular = 0.17*0.5 = 0.085 mol/L.
3. Apply the Nernst equation: E = (RT/zF) * ln([Ca2+]outside / [Ca2+]inside), where R is the ideal gas constant, T is the temperature in Kelvin, z is the valence of the ion, and F is the Faraday constant.
4. At body temperature (37°C), which is 310K, and using the constants R = 8.314 J/mol°K and F = 96485 C/mol, we can calculate the equilibrium potential.
5. Finally, we get the equilibrium potential for Ca2+ which in this case is positive, meaning the answer is either C or D from the provided options.

After performing the calculation with the correct values and units, we can find that the equilibrium potential for Ca2+ is approximately +37.5mV. Thus the correct answer is D. +37.5mV.