Which type of ion channel is activated by changes in the transmembrane voltage gradient?

• A. Ligand-gated ion channels
• B. Second messenger regulated ion channels
• C. Voltage-gated ion channels
• D. G-Protein coupled receptors

Answer: (C)

Voltage across the cell membrane serves as a gating signal for voltage-gated ion channels. They contain a voltage-sensing region with charged residues that respond to membrane depolarization by moving and opening the pore, allowing specific ions to flow. This direct voltage sensing is distinct from ligand-gated channels, which open when a chemical messenger binds, and from second messenger–regulated channels, which respond to intracellular signaling molecules. G-protein–coupled receptors regulate channels indirectly through signaling cascades rather than forming channels that open in response to voltage. So, channels that are activated directly by changes in the transmembrane voltage gradient are voltage-gated.