[Transporters for neurotransmitters. A new gene family with characteristic features]

Neurotransmitter transporters terminate synaptic transmission by rapid sodium-dependent reaccumulation of released transmitter in the presynaptic nerve terminal. The transporters are major sites of action for psychostimulants such as amphetamine and cocaine, for antidepressants, and for neurotoxins that induce parkinsonism. The transporters for monoamines, choline, GABA (gamma-aminobutyric acid), glycine and glutamine have recently been cloned and characterised. Elucidation of the primary structures has shown that, with the exception of the glutamate transporter, the various proteins manifest substantial amino acid conservation and the presence of 12 putative transmembrane regions. The lack of homology with other proteins suggests these transporter proteins to represent a new gene family. Preliminary findings suggest the distribution of neurotransmitter gene expression to match that of presynaptic markers of the respective transmitter systems, though in some areas the distribution of transporter mRNA expression has been found to be uneven. There is evidence suggesting neurotransmitter transporters to be involved in the pathophysiology of certain neurodegenerative diseases, and there are indications that drugs affecting transporter proteins may assume increasing clinical importance.