What characteristic makes voltage-gated potassium channels slow to open?

Voltage-gated potassium channels are crucial for the repolarization phase of action potentials in neurons and muscle cells. These channels are characterized by their sensitivity to changes in membrane potential. The correct characteristic that makes these channels slow to open is that they require a significant change of approximately 110 mV to activate.

This large change is due to the specific gating mechanism of these channels, which depends on the membrane potential becoming sufficiently positive. As the cell depolarizes, it reaches the threshold that activates the opening of the channels, but this process does not happen instantaneously. Instead, there is a delay following depolarization, during which time the conformational changes that lead to opening occur.

The need for a substantial depolarization before activation reflects the channel's role in ensuring that repolarization occurs only after a significant phase of depolarization has been achieved, thus contributing to the overall timing and shaping of action potentials. The other options do not accurately describe the mechanisms behind the slow opening of these channels. For instance, while voltage-gated potassium channels do respond to changes in membrane voltage, they do not open instantly upon depolarization, nor do they rely on an external energy source.