Hemicholinium-3 produces a cholinergic blockade that resembles, but is mechanistically distinct from, botulinum toxin. What is the precise site of action of hemicholinium-3?
- A Blocks the high-affinity choline re-uptake transporter (CHT1), depleting ACh stores ✓
- B Inhibits choline acetyltransferase, preventing acetylcholine synthesis
- C Cleaves SNAP-25, preventing vesicle fusion at the neuromuscular junction
- D Blocks nicotinic receptors at the motor end plate non-competitively
Correct answer: A. Blocks the high-affinity choline re-uptake transporter (CHT1), depleting ACh stores
Explanation
Hemicholinium-3 specifically inhibits CHT1, the sodium-dependent high-affinity choline transporter at cholinergic nerve terminals. Since choline re-uptake is the rate-limiting step for ACh synthesis, CHT1 blockade progressively depletes acetylcholine with repeated nerve stimulation. Botulinum toxin acts by cleaving SNARE proteins (SNAP-25, VAMP/synaptobrevin), while choline acetyltransferase inhibition is the target of compounds like BW284c51.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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