Choline is transported by vesicular acetylcholine transporter

Area of Science:

• Neuroscience
• Neurochemistry
• Molecular Biology

Background:

• Previous studies suggested the vesicular acetylcholine transporter (VAChT) does not transport choline (Ch).
• Choline is a crucial precursor for acetylcholine (ACh) synthesis and has potential roles as a neurotransmitter agonist.
• Re-evaluating VAChT substrate specificity is important for understanding cholinergic neurotransmission.

Purpose of the Study:

• To re-examine the transport selectivity of the vesicular acetylcholine transporter (VAChT) for choline (Ch).
• To investigate whether VAChT transports choline (Ch) using a sensitive assay for weak substrate binding.

Main Methods:

• Expressed rat VAChT in PC12(A1237) cells and prepared microvesicles.
• Employed a novel assay detecting transmembrane reorientation of the substrate binding site.
• Utilized unlabeled choline (Ch) and tetramethylammonium (TMA) in the reorientation assay.
• Performed an optimized accumulation assay using [(14)C]Ch and [(3)H]acetylcholine (ACh).

Main Results:

• Demonstrated that VAChT transports choline (Ch) with a sevenfold lower affinity than acetylcholine (ACh).
• Showed that tetramethylammonium (TMA) is also transported by VAChT, albeit with a 26-fold lower affinity.
• Confirmed choline (Ch) transport by VAChT using both reorientation and accumulation assays.

Conclusions:

• Vesicular acetylcholine transporter (VAChT) actively transports choline (Ch).
• The transport of choline (Ch) by VAChT has implications for cholinergic terminal function and regulation.
• Findings challenge prior assumptions about VAChT substrate specificity and highlight its role in choline homeostasis.