The human gene SLC18A1 encodes the vesicular monoamine transporter 1 (VMAT1) (Erickson JD et al, 1996). VMAT1 is mainly expressed in neuroendocrine cells. The human gene SLC18A2 encodes VMAT2 (Erickson JD and Eiden LE, 1993). Both transporters can mediate the transport of biogenic amines into secretory vesicles, which can then discharge their contents into the extracellular space by exocytosis. Predominant biogenic amines these proteins can transport are serotonin, dopamine, adrenaline, noradrenaline and histamine.