Answer:
Step-by-step explanation:
The Nernst equation describes the relationship between the equilibrium potential (also known as the Nernst potential) for an ion across a membrane and the concentration gradient of that ion. It is commonly used to calculate the equilibrium potential for a specific ion, such as potassium (K+), based on the intra- and extracellular concentrations of that ion.
The Nernst equation for a monovalent ion like potassium (K+) is as follows:
E = (RT/zF) * ln([K+]out/[K+]in)
Where:
E is the equilibrium potential for potassium (K+),
R is the ideal gas constant,
T is the absolute temperature,
z is the valence of the ion (for K+, z = 1),
F is Faraday's constant,
[K+]out is the extracellular concentration of potassium (K+),
[K+]in is the intracellular concentration of potassium (K+).
Now, if the current carried by K+ ions diffusing through a K+ channel is plotted against the membrane potential, the resulting curve is known as the current-voltage (I-V) relationship. Typically, the I-V relationship for a K+ channel is linear, indicating that the current increases as the membrane potential becomes more positive.
The reversal potential is the membrane potential at which the direction of the current carried by ions through a channel reverses. In the case of a K+ channel, the reversal potential is the membrane potential at which the net K+ current changes direction from outward (positive) to inward (negative). The reversal potential for a K+ channel is approximately equal to the equilibrium potential for potassium (E_K+), which can be calculated using the Nernst equation.
Therefore, at the membrane potential equal to the equilibrium potential for potassium (E_K+), the direction of the current carried by K+ ions through a K+ channel will reverse.