§1 Nernst Equation — Ion Equilibrium Potential
E = (RT / zF) · ln([X]out / [X]in)
The Nernst equation describes the equilibrium potential of a single ion across the membrane. When the membrane is permeable only to that ion, the membrane potential equals its equilibrium potential. Raising the temperature or increasing the concentration gradient increases the absolute value of the equilibrium potential.
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Parameters
°C
Equilibrium Potentials by Ion
| Ion | Valence z | [X]₀ (mM) | [X]ᵢ (mM) | E (mV) |
|---|---|---|---|---|
| K⁺ | 1.0000 | 5.0000 | 140.0000 | -89.0540 |
| Na⁺ | 1.0000 | 145.0000 | 15.0000 | 60.6312 |
| Ca²⁺ | 2.0000 | 2.0000 | 0.0001 | 132.3367 |
| Cl⁻ | -1.0000 | 110.0000 | 10.0000 | -64.0844 |