In a laboratory, scientists often study neurons in isolation, outside of a living

creature, in a dish. In this setting, one can have a good deal of control over the
local ionic environment in which the cell exists, because we can control the
makeup of the solution – the 'medium' – in the dish. This situation is a bit like
replacing the extracellular fluid that the cell would normally be bathed in with
some other fluid.!

There are a variety of different kinds of media that scientists use for different
purposes. Let’s consider a few standard ones, including Dulbecco’s Modified
Eagle’s Medium (DMEM)* and "depolarization" medium.!

The table below lists the ionic concentrations for these media. The "intracellular"
column lists the concentrations inside a particular neuron. All concentrations
below are in mM (millimolar).!
!
ion/ Intracellular/ DMEM /"depolarization medium"
K+ /140 /5.3/ 55
Na+ /10/ 154 /105
Cl- /12 /119/ 119
Ca2+/ 0.0001 /1.8/ 1.8

Based on this chart, what is the Nernst potential for K+ for the cell, bathed in
DMEM at 37C?!

Check the best option!
• 87 mV!
• -87 mV!
• -25 mV!
• 25 mV!
• -60 mV!

To calculate the Nernst potential for K+ in the given scenario, we need to use the Nernst equation:

E(K+) = (RT / zF) * ln([K+]out / [K+]in)

Where:
- E(K+) is the Nernst potential for K+.
- R is the gas constant (8.314 J/(mol·K)).
- T is the temperature in Kelvin (37C = 310K).
- z is the valence of the ion (K+ has a valence of 1).
- F is the Faraday constant (96,485 C/mol).
- [K+]out is the concentration of K+ in the extracellular medium (DMEM in this case).
- [K+]in is the concentration of K+ inside the neuron.

From the chart, we have:
[K+]out = 5.3 mM

Substituting these values into the equation:

E(K+) = (8.314 J/(mol·K) * 310K / (1 * 96,485 C/mol)) * ln(5.3 / 140)

Calculating this gives us:

E(K+) ≈ (-25 mV)

Therefore, the Nernst potential for K+ in the cell bathed in DMEM at 37C is approximately -25 mV. Therefore, the correct answer is:
• -25 mV!

To determine the Nernst potential for K+ in the cell, bathed in DMEM at 37°C, we need to calculate the equilibrium potential using the Nernst equation. The Nernst equation states that the equilibrium potential (in millivolts) for an ion can be calculated using the formula:

E = (RT/zF) * ln ([ion]out/[ion]in)

Where:
E = equilibrium potential
R = gas constant (8.314 J/(mol·K))
T = temperature in Kelvin (37°C = 310 K)
z = valence of the ion (in this case, K+ has a valence of +1)
F = Faraday constant (96,485 C/mol)
[ion]out = concentration of the ion outside the cell
[ion]in = concentration of the ion inside the cell

For K+ using DMEM, the [K+]out is 5.3 mM and the [K+]in is 140 mM. Plugging these values into the equation, we get:

E = (8.314 * 310 * ln(5.3/140))/(1 * 96485)

Calculating this equation gives us approximately -87 mV.

Therefore, the Nernst potential for K+ for the cell, bathed in DMEM at 37°C, is -87 mV.

So the correct option is: -87 mV.

Second Question:

What is the Nernst potential for Cl- in DMEM at 37C?!
Check the best option!
• 80 mV!
• -80 mV!
• 61 mV!
• -61 mV!

Third question:

What is the Nernst potential for Na+ in DMEM at 37C?!
Check the best option!
• 73 mV!
• -73 mV!
• 63 mV!
• -63 mV!

-25

80
63