Nernst potential for potassium
Extracellular K⁺ is 5 mM and intracellular K⁺ is 150 mM. Using E = (61.5 mV/z) log([out]/[in]) and log 30 ≈ 1.48, what is the K⁺ equilibrium potential at 37 °C?
Answer A: explanation for every choice
A
Correct. E = 61.5 × log(5/150) = 61.5 × (−1.48) ≈ −91 mV.
B
This assumes a 10-fold concentration ratio.
C
This divides by 2, as if K⁺ were divalent.
D
This reverses the ratio (in/out). K⁺ leaking out makes the inside negative.
TakeawayNernst: E = (61.5/z) log([out]/[in]) mV at body temperature.
Equation usedNernst equation
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