After its synthesis, acetylcholine (ACh) is packaged into vesicles. ACh is transported from the cytoplasm into individual vesicles by means of a carrier protein on the vesicle membrane called the vesicular ACh transporter (VAChT). VAChT is an antiporter that couples an influx of ACh with an efflux of protons (H+). Once packaged in a vesicle, acetylcholine is stored at the nerve ending until an action potential arrives and allows for its release into the synaptic cleft.