A neuropharmacology group tested a compound that inhibits the Na^+^+^+-70\ \text{mV}-55\ \text{mV}$. No acute change in voltage-gated channel kinetics was detected.
Which statement best explains the changes in membrane potential observed?
- Inhibiting the Na^+^+^+$ gradients over time, reducing the driving force that supports a negative resting potential. (correct answer)
- Inhibiting the Na^+^+^+$ import, making the membrane potential more negative.
- The drift to is best explained by immediate opening of voltage-gated Na channels producing an action potential upstroke.
- Inhibiting the Na^+^-V_m-55\ \text{mV}$.
Explanation: This question tests understanding of membrane potential and electrochemical gradients (Foundational Concept 2: Cells and Cellular Organization). The Na⁺/K⁺-ATPase maintains ion gradients by pumping 3 Na⁺ out and 2 K⁺ in, consuming ATP to work against concentration gradients. In this scenario, inhibiting the pump causes gradual depolarization from -70 mV to -55 mV as ion gradients dissipate. Choice A is correct because without the pump's activity, Na⁺ gradually accumulates inside while K⁺ decreases inside, reducing both the K⁺ and Na⁺ concentration gradients that normally support the negative resting potential, causing the membrane potential to drift toward a less polarized state. Choice B is incorrect because it reverses the pump's function - the Na⁺/K⁺-ATPase exports Na⁺ and imports K⁺, not the opposite. To avoid confusion, remember that the pump maintains gradients that passive channels then use to generate membrane potential, and inhibiting the pump causes gradual gradient dissipation rather than immediate channel effects.