Question

The extracellular K+ concentration ([K]) increases from the normal of 4 mM to 10 mM. What is K+ equilibrium potential when [K] is 4mM and 10 mM, respectively, given that intracellular K+ is 135mM?

Answer 1

The equilibrium potential for potassium
`(\(K^+\))` is determined by the Nernst equation. When [K] is 4 mM outside and 135 mM inside, the equilibrium potential is -86.6 mV. Similarly, when [K] is 10 mM outside, the potential becomes -61.5 mV. This shift reflects the influence of extracellular potassium concentration on the ion's equilibrium potential.

Step-by-step explanation:

The equilibrium potential of an ion, determined by the Nernst equation, reflects the balance between the concentration gradients of that ion across a cell membrane. In the case of potassium
`(\(K^+\))`, the equation is given by
`\(E_{\text{K}} = (RT)/(zF) \ln\left(\frac{[K]_{\text{outside}}}{[K]_{\text{inside}}}\right)\)`. When the extracellular concentration of potassium is 4 mM and the intracellular concentration is 135 mM, the resulting equilibrium potential
`(\(E_{\text{K}}\))` is -86.6 mV. This negative value signifies that the inside of the cell is more negatively charged relative to the extracellular space, consistent with the resting membrane potential of many cells.

When the extracellular potassium concentration increases to 10 mM while the intracellular remains at 135 mM, the equilibrium potential shifts to -61.5 mV. This shift indicates a decrease in the membrane potential, making the inside of the cell less negatively charged. Such alterations in potassium concentrations can impact cell excitability and contribute to changes in cellular functions like neuronal signaling and muscle contraction.

Understanding the Nernst equation's application to potassium equilibrium potential provides insights into the electrochemical dynamics crucial for cellular physiology and underscores the sensitivity of cell behavior to ionic concentrations in their microenvironment.