piperidines and tetraphenylphosphonium

The acetylcholine-binding site in vesicular acetylcholine transporter faces predominantly toward the outside of the vesicle when resting but predominantly toward the inside when transporting. Transport-related reorientation is detected by an ATP-induced decrease in the ability of saturating substrate to displace allosterically bound [(3)H]vesamicol. The assay was used here to determine whether structurally diverse compounds are transported by rat VAChT expressed in PC12(A123.7) cells. Competition by ethidium, tetraphenylphosphonium and other monovalent organic cations with [(3)H]vesamicol is decreased when ATP is added, and the effect depends on proton-motive force. The results indicate that many organic molecules carrying +1 charge are transported, even though the compounds do not resemble acetylcholine in structural details.

Topics: Acetylcholine; Adenosine Triphosphate; Allosteric Regulation; Animals; Binding Sites; Binding, Competitive; Biological Transport, Active; Cations; Ethidium; Membrane Transport Proteins; Molecular Structure; Neuromuscular Depolarizing Agents; Neurons; Onium Compounds; Organophosphorus Compounds; PC12 Cells; Piperidines; Rats; Synaptic Transmission; Synaptic Vesicles; Vesicular Acetylcholine Transport Proteins