|Chemical and physical data|
|Molar mass||414.538 g/mol|
|3D model (JSmol)|
|(what is this?)|
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.
Hemicholinium-3 has no clinical use, but is frequently used as a research tool in animal and in vitro experiments. The clinical use is limited since it prevents uptake into the cell which is not a rate limiting factor under normal, physiological frequencies of activation. This type of inhibition only becomes apparent at excessively high firing rates, whereby the uptake of choline into the nerve terminal as a rate limiting factor becomes apparent.
Hemicholinium-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.