Identification of differentiation-associated brain-specific phosphate transporter as a second vesicular glutamate transporter (VGLUT2).
Glutamate is the major excitatory neurotransmitter in mammalian CNS. In the presynaptic nerve terminal, glutamate is stored in synaptic vesicles and released by exocytosis. Previously, it has been shown that a transport protein originally identified as a brain-specific Na(+)-dependent inorganic phosphate transporter I (BNPI) functions as vesicular glutamate transporter and thus has been renamed VGLUT1. Recently, a protein highly homologous to VGLUT1, "differentiation-associated BNPI" (DNPI), has been discovered. Northern blot and in situ hybridization analyses indicate that DNPI mRNA is expressed in some brain regions in which VGLUT1 mRNA is not expressed. We now show that DNPI functions as vesicular glutamate transporter with properties very similar to VGLUT1 and propose to rename the protein VGLUT2. VGLUT2 is highly enriched in synaptic vesicles. Furthermore, VGLUT2 resides on a vesicle population that is distinct from vesicles containing the vesicular GABA transporter or VGLUT1, showing that the expression of VGLUT1 and VGLUT2 do not overlap. When VGLUT2 was expressed in BON cells, membrane fractions displayed ATP-dependent, carbonyl cyanide p-trifluoromethoxyphenylhydrazone-sensitive glutamate uptake. Overexpression of VGLUT2 in cultured autaptic GABAergic neurons yielded postsynaptic currents that were insensitive to the GABA(A) receptor antagonist bicuculline but blocked by the AMPA-receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfonyl-benzo[F]quinoxaline. Thus, expression of VGLUT2 suffices to cause GABAergic neurons to release glutamate in addition to GABA in a manner very similar to that reported previously for VGLUT1.
Takamori
S
S
Departments of Neurobiology and Membrane Biophysics, Max-Planck-Institute for Biophysical Chemistry, D-37077 Göttingen, Germany.
Rhee
J S
JS
Rosenmund
C
C
Jahn
R
R
D000818:Animals; D000918:Antibody Specificity; D001692:Biological Transport; D001921:Brain / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation; D002460:Cell Line; D002478:Cells, Cultured; D050485:GABA Plasma Membrane Transport Proteins; D018698:Glutamic Acid / Q000378:metabolism*; D006801:Humans; D017403:In Situ Hybridization; D008565:Membrane Proteins / Q000378:metabolism; D026901:Membrane Transport Proteins; D051379:Mice; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D009928:Organ Specificity; D027361:Organic Anion Transporters; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D013347:Subcellular Fractions / Q000378:metabolism; D013572:Synaptic Vesicles / Q000378:metabolism; D014162:Transfection; D050598:Vesicular Glutamate Transport Protein 1; D050599:Vesicular Glutamate Transport Protein 2; D033921:Vesicular Transport Proteins; D005680:gamma-Aminobutyric Acid / Q000378:metabolism / Q000493:pharmacokinetics
D002352:Carrier Proteins; D050485:GABA Plasma Membrane Transport Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D027361:Organic Anion Transporters; D012333:RNA, Messenger; C493476:SLC17A6 protein, human; C493464:SLC17A7 protein, human; C493477:Slc17a6 protein, mouse; C493475:Slc17a6 protein, rat; C493465:Slc17a7 protein, mouse; C493466:Slc17a7 protein, rat; D050598:Vesicular Glutamate Transport Protein 1; D050599:Vesicular Glutamate Transport Protein 2; D033921:Vesicular Transport Proteins; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid