What is the mechanism of action of local anesthetics?

Correct answer: A. Sodium channel blocker

• A. Local anesthetics (lidocaine, articaine, bupivacaine, etc.) work by BLOCKING VOLTAGE-GATED SODIUM CHANNELS in nerve membranes. In their uncharged free-base form, they cross the lipid bilayer; once inside the neuron, they convert to the charged (ionized) form that blocks the Na+ channel from INSIDE. This prevents the Na+ influx needed for action potential generation and propagation, blocking nerve conduction. No Na+ influx = no action potential = no pain signal.
• B. Opening K+ channels would cause hyperpolarization — but local anesthetics work by BLOCKING Na+ channels, not opening K+ channels.
• C. GABA receptor enhancement is the mechanism of benzodiazepines and barbiturates — NOT local anesthetics.
• D. Calcium channel blockers (like verapamil) affect cardiac and vascular smooth muscle — NOT the mechanism of local anesthetic action.