If compartment A represents the inside of a cell and compartment B the extracellular fluid, then with [K]i = 100 mM and [K]o = 10 mM as in the example above calculate the equilibrium potential for potassium.

To calculate the equilibrium potential for potassium (K⁺), you can use the Nernst equation, which is given by:

[ E_{K} = frac{RT}{zF} ln left( frac{[K]_{o}}{[K]_{i}} right) ]

Where:

– ( E_{K} ) is the equilibrium potential for potassium.

– ( R ) is the universal gas constant (8.314 J/(mol·K)).

– ( T ) is the temperature in Kelvin (usually 310 K for physiological conditions).

– ( z ) is the charge of the ion (+1 for K⁺).

– ( F ) is Faraday’s constant (96485 C/mol).

For simplicity, at physiological temperature (37°C or 310 K), you can also use the simplified version of the Nernst equation:

[

E_{K} approx 61.5 , text{mV} cdot log left( frac{[K]_{o}}{[K]_{i}} right)

]

Plugging in the values:

– ([K]_{o} = 10 , text{mM})

– ([K]_{i} = 100 , text{mM})

We get:

[

E_{K} approx 61.5 , text{m