Question 27: “If a neuronal membrane were to become suddenly impermeable to potassium ions but retain an active “Na+/K+ ATPase, the neuron’s resting potential would:”
Here, when it says that the membrane is impermeable to potassium ions, is it referring to voltage gated potassium channels, or some other type of channel? Assuming that it is some other type of channel, is A the right answer because potassium can’t diffuse out anymore but more potassium keeps coming in due to the ATPase?
Recall that the resting potential is established by the diffusion of K+ ions out of the cell through non-voltage gated channels (“leak channels”) in the membrane. The Na+/K+ ATPase maintains a high intracellular concentration of K+ relative to the extracellular environment by pumping 2 K+ ions into the cell (and 3 Na+ ions out of the cell).
If the membrane were to become impermeable to K+ ions (i.e. the membrane would not allow the passive efflux of K+ ions out of the cell through these “leak channels”) but the Na+/K+ ATPase continued as normal, then K+ ions would continue to enter the cell via the Na+/K+ ATPase but no K+ ions would leave. Thus, the K+ concentration inside the cell would be greater than if the membrane were permeable to K+ ions (and accordingly, the resting potential would become more positive, answer choice A).