Which of the following is an example of a voltage-gated ion channel?

• A. The calcium-activated potassium channel
• B. A ligand-gated ion channel
• C. The sodium and potassium voltage-gated channel of nerve and muscle
• D. An intracellular receptor

Answer: (C)

Voltage-gated ion channels open or close in direct response to changes in the membrane potential, not to chemical binding. This voltage sensitivity lets them act as rapid gates during electrical signaling, such as the initiation and propagation of action potentials.

The example described—the voltage-gated sodium and potassium channel in nerve and muscle—embodies this property. When the membrane depolarizes, voltage-sensing regions respond and open the sodium channels to drive the rapid upstroke of the action potential, followed by potassium channels that open to repolarize the membrane. This sequence relies on voltage changes across the membrane to control gating.

In contrast, calcium-activated potassium channels require intracellular calcium to bind for opening, and ligand-gated channels open when a specific molecule (like a neurotransmitter) binds to the channel or receptor, not due to voltage. An intracellular receptor isn’t an ion channel at all; it’s a receptor inside the cell that mediates signaling or gene expression rather than forming an ion pore in response to membrane potential.