[K+] outside = 10 mEq/L and [K+] inside = 150 mEq/L.
What effect would reducing the extracellular fluid potassium (K+)
concentration from 5mM to 1mM have on RMP and why.
To determine the effect of reducing the extracellular fluid potassium (K+) concentration from 5mM to 1mM on the resting membrane potential (RMP), we need to consider the role of potassium in establishing the RMP.
The RMP is the electrical potential difference across the membrane of a cell when it is at rest. It is primarily determined by the distribution of ions across the membrane, particularly potassium ions (K+), sodium ions (Na+), and chloride ions (Cl-).
In a resting state, the membrane is more permeable to potassium ions, allowing them to leak out of the cell, while the sodium and chloride ions are maintained at higher concentrations inside the cell. This differential distribution of ions creates a negative charge inside the cell relative to the outside, resulting in the RMP.
Now, let's consider the effect of reducing the extracellular fluid potassium concentration from 5mM to 1mM:
1. Decreased Extracellular Potassium (K+): When the extracellular K+ concentration is lowered, it reduces the concentration gradient across the cell membrane. This, in turn, reduces the driving force for potassium to move out of the cell during the resting state.
2. Effect on Resting Membrane Potential (RMP): Since the RMP is primarily determined by the movement of potassium ions, a decrease in extracellular K+ concentration would lead to a less negative RMP, resulting in a depolarization of the cell. This means that the membrane potential would be closer to zero or potentially more positive than the normal RMP.
In summary, reducing the extracellular fluid potassium concentration from 5mM to 1mM would lead to a less negative resting membrane potential (depolarization) because of the reduced concentration gradient for potassium ions to move out of the cell.
To determine the effect of reducing the extracellular fluid potassium (K+) concentration on the resting membrane potential (RMP), we need to understand the concept of the Nernst equation.
The Nernst equation calculates the equilibrium potential for a specific ion across a cell membrane and is given by:
E = (RT / zF) * ln([ion]outside / [ion]inside)
Where:
- E is the equilibrium potential
- R is the gas constant
- T is the temperature in Kelvin
- z is the valence of the ion
- F is Faraday's constant
- [ion]outside is the extracellular ion concentration
- [ion]inside is the intracellular ion concentration
- ln represents the natural logarithm
In this case, we are interested in the equilibrium potential for potassium (K+). By using the Nernst equation, we can calculate the equilibrium potential for K+ under two different extracellular concentrations (5mM and 1mM) and compare the results.
Step 1: Converting concentrations to mEq/L:
To use the Nernst equation, we need to convert the concentrations from mM to mEq/L. This can be done by considering the molar mass of potassium.
1 mM of K+ = 1 mmol/L
1 mmol of K+ = 1 milliequivalent (mEq) of K+
Therefore, a 5 mM concentration of K+ is equal to 5 mEq/L, and a 1 mM concentration of K+ is equal to 1 mEq/L.
Step 2: Calculating the equilibrium potentials:
Now, we can compute the equilibrium potentials using the Nernst equation for both concentrations:
For [K+] outside = 5 mEq/L:
E1 = (RT / zF) * ln([ion]outside / [ion]inside)
= (RT / zF) * ln(5 mEq/L / 150 mEq/L)
For [K+] outside = 1 mEq/L:
E2 = (RT / zF) * ln([ion]outside / [ion]inside)
= (RT / zF) * ln(1 mEq/L / 150 mEq/L)
Step 3: Comparing the equilibrium potentials:
Now, we can compare the calculated equilibrium potentials (E1 and E2) to determine the effect on the resting membrane potential (RMP).
If the extracellular K+ concentration is reduced from 5 mM to 1 mM (5 mEq/L to 1 mEq/L), the equilibrium potential for K+ (E) will change. However, the RMP is determined by the concentration and permeability of all ions (not just K+), so it may not directly reflect the change in K+ concentration.
To fully assess the effect on the RMP, one must also consider the permeability of other ions (such as Na+ or Cl-) and their respective equilibrium potentials.
Therefore, the change in extracellular K+ concentration alone may not be sufficient to determine the exact effect on the resting membrane potential. It is important to consider the contribution of other ions and their permeability in the calculation.