Cloning and functional characterization of a high-affinity Na(+)/dicarboxylate cotransporter from mouse brain.
Neurons contain a high-affinity Na(+)/dicarboxylate cotransporter for absorption of neurotransmitter precursor substrates, such as alpha-ketoglutarate and malate, which are subsequently metabolized to replenish pools of neurotransmitters, including glutamate. We have isolated the cDNA coding for a high-affinity Na(+)/dicarboxylate cotransporter from mouse brain, called mNaDC-3. The mRNA coding for mNaDC-3 is found in brain and choroid plexus as well as in kidney and liver. The mNaDC-3 transporter has a broad substrate specificity for dicarboxylates, including succinate, alpha-ketoglutarate, fumarate, malate, and dimethylsuccinate. The transport of citrate is relatively insensitive to pH, but the transport of succinate is inhibited by acidic pH. The Michaelis-Menten constant for succinate in mNaDC-3 is 140 microM in transport assays and 16 microM at -50 mV in two-electrode voltage clamp assays. Transport is dependent on sodium, although lithium can partially substitute for sodium. In conclusion, mNaDC-3 likely codes for the high-affinity Na(+)/dicarboxylate cotransporter in brain, and it has some unusual electrical properties compared with the other members of the family.
Pajor
A M
AM
Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston, Texas 77555, USA. ampajor@utmb.edu
Gangula
R
R
Yao
X
X
D000595:Amino Acid Sequence; D000818:Animals; D001921:Brain / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D003001:Cloning, Molecular; D016384:Consensus Sequence; D005260:Female; D005399:Fishes; D015723:Gene Library; D006801:Humans; D007700:Kinetics; D008564:Membrane Potentials / Q000502:physiology; D026901:Membrane Transport Proteins; D051379:Mice; D008969:Molecular Sequence Data; D009865:Oocytes / Q000502:physiology; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D013386:Succinates / Q000378:metabolism*; D027981:Symporters; D014982:Xenopus laevis
D002352:Carrier Proteins; D026901:Membrane Transport Proteins; D011994:Recombinant Proteins; C425791:Slc13a3 protein, mouse; D013386:Succinates; D027981:Symporters