Blocking potassium ion channels in a mammalian cell membrane would __________.

• A. increase the resting potential
• B. increase potassium's equilibrium potential
• C. decrease sodium's equilibrium potential
• D. increase the magnitude of the membrane potential
• E. decrease the magnitude of the membrane potential

Answer: (E)

Verified step by step guidance

1. Understand the role of potassium ion channels: Potassium ion channels are crucial for maintaining the resting membrane potential in cells by allowing potassium ions (K⁺) to move out of the cell, which helps balance the charge across the membrane.
2. Consider the effect of blocking potassium ion channels: If these channels are blocked, potassium ions cannot exit the cell as they normally would, which affects the distribution of charge across the membrane.
3. Analyze the impact on membrane potential: Normally, the movement of K⁺ out of the cell makes the inside of the cell more negative. Blocking these channels would prevent this movement, leading to a less negative (or more positive) inside compared to the outside.
4. Relate to membrane potential magnitude: The membrane potential is the difference in charge across the cell membrane. If the inside becomes less negative due to blocked K⁺ channels, the difference in charge (magnitude of membrane potential) decreases.
5. Conclude the effect: Therefore, blocking potassium ion channels would decrease the magnitude of the membrane potential, as the charge difference across the membrane is reduced.