Synaptic vesicles are capable of synthesizing the VGLUT substrate glutamate from α-ketoglutarate for vesicular loading

J Neurochem. 2012 Apr;121(2):184-96. doi: 10.1111/j.1471-4159.2012.07684.x. Epub 2012 Mar 13.

Abstract

Synaptic vesicle loading of glutamate is a pivotal step in glutamate synaptic transmission. The molecular machinery responsible for this step is comprised of v-type proton-pump ATPase and a vesicular glutamate transporter. Recent evidence indicates that synaptic vesicles are endowed with glycolytic ATP-synthesizing enzymes, providing energy for immediate use by vesicle-bound proton-pump ATPase. In this study, we provide evidence that synaptic vesicles are also capable of synthesizing the vesicular glutamate transporter substrate glutamate, from α-ketoglutarate and l-aspartate (as the amino group donor); glutamate thus produced is taken up into vesicles. We also report a finding that α-ketoglutarate-derived glutamate uptake into synaptic vesicles and aspartate aminotransferase are inhibited by 2,3-pyrazinedicarboxylate. Evidence is given that this is a selective inhibitor for aspartate aminotransferase. These observations provide insight into understanding the nerve endings' mechanism for high efficiency in glutamate transmission. Finding this inhibitor may have implications for further experimentation on the role of α-ketoglutarate-derived glutamate in glutamate transmission.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Aspartate Aminotransferases / antagonists & inhibitors
  • Aspartate Aminotransferases / metabolism
  • Aspartic Acid / metabolism
  • Blotting, Western
  • Chromatography, High Pressure Liquid
  • Enzyme Inhibitors / pharmacology
  • Glutamate Dehydrogenase / metabolism
  • Glutamic Acid / biosynthesis*
  • Glutaminase / metabolism
  • In Vitro Techniques
  • Indicators and Reagents
  • Ketoglutaric Acids / metabolism*
  • Male
  • Mitochondria / enzymology
  • Proton-Translocating ATPases / metabolism
  • Rats
  • Subcellular Fractions / drug effects
  • Subcellular Fractions / metabolism
  • Synaptic Vesicles / metabolism*
  • Synaptosomes / drug effects
  • Synaptosomes / metabolism
  • Vesicular Transport Proteins / metabolism*

Substances

  • Enzyme Inhibitors
  • Indicators and Reagents
  • Ketoglutaric Acids
  • Vesicular Transport Proteins
  • Aspartic Acid
  • Glutamic Acid
  • Glutamate Dehydrogenase
  • Aspartate Aminotransferases
  • Glutaminase
  • Proton-Translocating ATPases