A molecular analysis of vesicular amine transport

To package classical neurotransmitters into vesicles so that their release can be regulated by activity, neuronal cells express a set of specific vesicular transport proteins. We have used selection in MPP+ to clone the cDNAs encoding two vesicular monoamine transporters, the first members of this novel gene family that now also includes the vesicular transporter for acetylcholine. The sequences show similarity to several bacterial antibiotic resistance proteins, further supporting a role in detoxification and possibly Parkinson's disease. The two vesicular amine transporters show differences in their affinity for substrates, their turnover number and their pharmacology. In particular, the proteins differ in their interactions with the potent inhibitor tetrabenazine and with amphetamines, accounting for several classic pharmacological observations. Since the subcellular localization of the transport proteins determines the site of monoamine storage and the site of monoamine storage appears to differ from other classical transmitters, we have also raised polyclonal antibodies to the transporters and used these to demonstrate localization in dense core vesicles rather than synaptic vesicles. In addition to the implications for monoamine release, these observations also indicate a vesicular amine transporter as the first integral membrane protein restricted to the regulated secretory pathway.