Choline is transported by vesicular acetylcholine transporter.
Previously published results appeared to show that vesicular acetylcholine transporter (VAChT) does not transport choline (Ch). Because it is uniquely suited to detect transport of weakly bound substrates, a recently developed assay that detects transmembrane reorientation of the substrate binding site was used to re-examine transport selectivity. Rat VAChT was expressed in PC12(A1237) cells, postnuclear supernatant-containing microvesicles was prepared, and the reorientation assay was conducted with unlabeled Ch and tetramethylammonium (TMA). Also, [(14)C]Ch and [(3)H]acetylcholine (ACh) were used in an optimized accumulation assay. The results demonstrate that Ch is transported at least as well as ACh is, but with sevenfold lower affinity. Even TMA is transported, but with 26-fold lower affinity. Ch transport by VAChT is of interest in view of the possibilities that Ch (i) occurs at higher concentration than ACh does in terminal cytoplasm under some conditions, and (ii) is an agonist for alpha 7 nicotinic receptors.
Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106-9510, USA.
Dawn T
DT
Bravo
Natalia G
NG
Kolmakova
Stanley M
SM
Parsons
D000109:Acetylcholine / Q000737:chemistry / Q000378:metabolism / Q000493:pharmacokinetics; D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D001692:Biological Transport / Q000187:drug effects; D002250:Carbon Radioisotopes; D002794:Choline / Q000737:chemistry / Q000378:metabolism* / Q000493:pharmacokinetics; D007425:Intracellular Membranes / Q000737:chemistry / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D016716:PC12 Cells; D010880:Piperidines / Q000737:chemistry / Q000493:pharmacokinetics; D000644:Quaternary Ammonium Compounds / Q000737:chemistry / Q000378:metabolism / Q000493:pharmacokinetics; D011869:Radioligand Assay; D051381:Rats; D013347:Subcellular Fractions / Q000737:chemistry / Q000378:metabolism; D014316:Tritium; D050494:Vesicular Acetylcholine Transport Proteins
D002250:Carbon Radioisotopes; D026901:Membrane Transport Proteins; D010880:Piperidines; D000644:Quaternary Ammonium Compounds; C493461:Slc18a3 protein, rat; D050494:Vesicular Acetylcholine Transport Proteins; D014316:Tritium; C006189:vesamicol; C027917:tetramethylammonium; D002794:Choline; D000109:Acetylcholine