Hemicholinium-3

Hemicholinium-3 (HC3), also known as hemicholine, is a drug which blocks the reuptake of choline by the high-affinity choline transporter (ChT; encoded in humans by the gene SLC5A7) at the presynapse. The reuptake of choline is the rate limiting step in the synthesis of acetylcholine; hence, hemicholinium-3 decreases the synthesis of acetylcholine. It is therefore classified as an indirect acetylcholine antagonist.

Acetylcholine is synthesized from choline and a donated acetyl group from acetyl-CoA, by the action of choline acetyltransferase (ChAT). Thus, decreasing the amount of choline available to a neuron will decrease the amount of acetylcholine produced. Neurons affected by hemicholinium-3 must rely on the transport of choline from the soma (cell body), rather than relying on reuptake of choline from the synaptic cleft.

Effects
Hemicholinium-3 has no clinical use, but is frequently used as a research tool in animal and in vitro experiments.

Hemoicholinium-3 produces a decrease in acetylcholine content in the nerve terminal and as a consequence results in a decrease in acetylcholine transmission. Since acetylcholine normally binds to nicotinic and muscarinic receptors in synapses, a decrease in acetylcholine would cause a decrease in nicotinic and muscarinic pharmacology.