Abstract
We assayed glutamate transport activity in cultures of rat cortical neurons containing <0.2% astrocytes. Using [3H]l-glutamate as the tracer, sodium-dependent high affinity glutamate transport was demonstrated [K m = 17.2 ± 2.4 μm; V max = 3.3 ± 0.32 nmol/mg of protein/min (n = 5)]. Dihydrokainate (1 mm) inhibited uptake of radioactivity by 88 ± 3% and had aK i value of 65 ± 7 μm. l-α-Aminoadipate (1 mm) inhibited uptake by only 25 ± 4%.l-trans-2,4-Pyrrolidine dicarboxylate,l-serine-O-sulfate, and kainate potently inhibited transport activity withK i values of 5.1 ± 0.3, 56 ± 6, and 103 ± 9 μm, respectively (n = 3). Voltage-clamp studies of GLT1-expressing oocytes showed that, as in cortical neurons, glutamate transport was not inhibited by l-α-aminoadipate. Dihydrokainate was a potent inhibitor (K i = 8 ± 1 μm), andl-serine-O-sulfate produced a GLT1-mediated current with a K mvalue of 312 ± 33 μm. Immunoblot analysis showed that neuronal cultures express excitatory amino acid carrier 1 (EAAC1), shown previously to be relatively insensitive to dihydrokainate, plus a trace amount of GLT1, but no GLAST. These studies establish that a major component of the glutamate transport activity of cortical neurons is dihydrokainate sensitive and distinct from the previously recognized neuronal transporter excitatory amino acid carrier 1.
Footnotes
- Received May 30, 1997.
- Accepted September 26, 1997.
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Send reprint requests to: Dr. Paul A. Rosenberg, Enders Research Building, Department of Neurology, Children’s Hospital, 300 Longwood Avenue, Boston MA 02115. E-mail:rosenberg{at}a1.tch.harvard.edu
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This work was supported by National Institutes of Health Grants NS33270 (M.P.K.) and NS31353 and a Mental Retardation Core Grant to Children’s Hospital (P.A.R.) and by grants from the United Cerebral Palsy Foundation, Ron Shapiro Charitable Foundation, and Muscular Dystrophy Association (P.A.R.). G.J.W. and H.J.C. contributed equally to this work.
- The American Society for Pharmacology and Experimental Therapeutics
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