Final answer:
Measuring end plate current (EPC) using a voltage clamp shows that EPC decreases during hyperpolarization when the membrane potential (Vm) is less than the resting membrane potential. Conversely, EPC increases during depolarization when Vm is greater than the resting membrane potential.
Step-by-step explanation:
When measuring end plate current (EPC) with a voltage clamp, the EPC will vary depending on the membrane potential (Vm). Normally, at rest, Vm is about -70 mV. If Vm is set to a value less than the resting membrane potential (Vm < resting Vm), the end plate will be hyperpolarized. During hyperpolarization, the influx of positive ions (typically Na+ for EPC) through the ligand-gated ion channels at the neuromuscular junction is reduced. This hyperpolarization results in a smaller end plate current, as fewer positively charged ions enter the cell. Conversely, if Vm was set to a value above the resting membrane potential (Vm > resting Vm), this would lead to depolarization, and an increased flow of ions, thus, increasing the EPC.