Membrane Potential and Electrochemical Gradients (2A) Practice Test

In a patch-clamp experiment, a neuron is initially at rest (−70 mV). A toxin that selectively blocks voltage-gated K\(^+\) channels is applied. When an action potential is triggered by a brief current injection, the repolarization phase becomes slower and the after-hyperpolarization is reduced.

Which statement best explains the changes in membrane potential observed?

A neuron has intracellular K\(^+\) 140 mM and extracellular K\(^+\) 4 mM. A researcher injects KCl into the cytosol, increasing intracellular Cl\(^−\) substantially while leaving K\(^+\) nearly unchanged. Opening GABA\(_A\) receptors (Cl\(^−\) channels) now produces depolarizing responses instead of hyperpolarizing responses.

Which statement best explains the change in response polarity?