Practice Test 3

In a neuron, resting permeability is dominated by K\(^+\) leak channels. A researcher applies a selective blocker of K\(^+\) leak channels (not voltage-gated K\(^+\) channels). Resting membrane potential shifts from −70 mV to −55 mV.

Which statement best explains the changes in membrane potential observed?

In a whole-cell patch-clamp experiment on cultured hippocampal neurons, baseline resting membrane potential is measured at $-70\ \text{mV}$. A selective ligand-gated channel is activated that increases membrane permeability to K$^+$ but not to Na$^+$, Cl$^-$, or Ca$^{2+}$. Ion concentrations (mM) are stable during the brief recording: intracellular K$^+$ = 140, extracellular K$^+$ = 4; intracellular Na$^+$ = 12, extracellular Na$^+$ = 145; intracellular Cl$^-$ = 10, extracellular Cl$^-$ = 110. Based on the scenario, what effect would increasing K$^+$ permeability have on the membrane potential observed immediately after channel activation?