Vesamicol inhibits transmitter storage by blocking which transporter?

• A. Transmitter synthesis
• B. Transmitter release
• C. Transmitter storage
• D. Transmitter uptake

Answer: (C)

The key idea is how transmitter storage in vesicles works. Neurons load acetylcholine into synaptic vesicles using a specific vesicular transporter, which uses the proton gradient established in the vesicle to pump the transmitter inside. Vesamicol directly blocks this vesicular acetylcholine transporter, so acetylcholine cannot be packed into vesicles. Without proper storage, little transmitter is ready for release when the neuron fires, reducing cholinergic signaling.

Synthesis creates acetylcholine in the cytosol and is not blocked by Vesamicol. Release involves the exocytosis of vesicles, which depends on vesicle loading but is not prevented by Vesamicol itself. Uptake refers to reabsorption of transmitter from the synaptic space back into the neuron via reuptake transporters, which Vesamicol does not affect. Therefore, the transporter blocked by Vesamicol is the vesicular acetylcholine transporter responsible for transmitter storage.