The Nernst potential for ions can be calculated using the Nernst equation, which requires knowledge of the ion's concentration gradient across a membrane and the temperature in kelvins. For biological systems at 37°C, the equation includes the specific values for the temperature, gas constant, Faraday constant, and number of moles of electrons transferred.
To calculate the Nernst potential for Cl- in DMEM or for K+ in a depolarization medium at 37°C, we can apply the Nernst equation. This equation relates cell potentials to changes in Gibbs free energy and is given by:
E = E° - ∂(RT/nF) ∂lnQ
where E is the cell potential, E° is the standard cell potential, R is the gas constant (8.314 J/mol·K), T is the temperature in kelvins, n is the number of moles of electrons transferred in the reaction, F is the Faraday constant (96485 C/mol), and Q is the reaction quotient.
For standard conditions (standard pressure and solutions at 1 M concentration), E° can be found in tables of standard reduction potentials. However, for non-standard conditions, such as those in the DMEM (Dulbecco's Modified Eagle Medium) or during cellular depolarization, we must know the actual concentrations or activities of the involved species.
In the case of biological systems, the temperature is often 37°C (310 K) rather than the standard 298 K, so the Nernst equation must be adjusted for this temperature. The modified equation for the potential difference for an ion across a membrane is given by:
E = E° − (RT/nF) ∂ln([ion outside]/[ion inside])
For Cl- and K+ ions, we would use their respective concentrations inside and outside the cell to calculate the Nernst potentials.