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Nernst Equation

Each ion has an equilibrium potential associated with it whereby the diffusive forces and the electrical forces balance. This is given by the Nernst Equation  
E_i \equiv V_{in}-V_{out} = \frac{RT}{zF} \ln
\frac{[C]_{out}}{[C]_{in}}\end{displaymath} (1)
where T is the absolute temperature $ 273.16 + {}^\circ C$,$R=8.31451 \ j/(mol- K)$ is the ideal gas constant, $F=96485.3\
C/mol$ is Faraday's constant, and z is the valence of the ion. Generally people use the logarithm base 10 in which case the Nernst equation is multiplied by the factor 2.303. At $T=20^\circ C$ just multiply the logarithm base 10 of the ratio of outside to inside by 58 mV to get the equilibrium potential. At $T=37^\circ C$ the multiplication factor is just 62 mV. The table at the end of this section shows the typical equilibrium potentials for various membranes at various temperatures.

G. Bard Ermentrout