Functional expression of a GLT-1 type Na+-dependent glutamate transporter in rat pinealocytes

Hiroshi Yamada, Shouki Yatsushiro, Akitsugu Yamamoto, Mitsuko Hayashi, Tsuyoshi Nishi, Masamitsu Futai, Akihito Yamaguchi, Yoshinori Moriyama

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Abstract

Pinealocytes, the neuroendocrine cells that produce melatonin, accumulate glutamate in microvesicles through a specific vesicular transporter energetically coupled with vacuolar-type proton ATPase. The glutamate is secreted into the extracellular space through microvesicle- mediated exocytosis and then stimulates neighboring pinealocytes, resulting in inhibition of norepinephrine-dependent melatonin synthesis. In this study, we identified and characterized the plasma membrane-type glutamate transporter in rat pinealocytes. The [3H]-glutamate uptake by cultured pinealocytes was driven by extracellular Na+, saturated with the [3H]glutamate concentration used, and significantly inhibited by L- glutamate, L-aspartate, β-threo-hydroxyaspartate, pyrrolidine dicarboxylate, and L-cysteine sulfinate, substrates or inhibitors of the plasma membrane glutamate transporter. Consistently, the clearance of extracellular glutamate, as measured by HPLC, was also dependent on Na+ and inhibited by β-threo-hydroxyaspartate and L-cysteine sulfinate. Immunological studies with site-specific antibodies against three isoforms of the Na+-dependent glutamate transporter (GLT-1, GLAST, and EAAC1) revealed the expression of only the GLT-1 type transporter in pineal glands. Expression of the GLT-1 type transporter in pineal glands was further demonstrated by means of reverse transcription-polymerase chain reaction with specific DNA probes. Immunohistochemical analysis indicated that the immunological counterpart(s) of the GLT-1 is localized in pinealocytes. These results suggested that the GLT-1-type Na+-dependent transporter is expressed and functions as a reuptake system for glutamate in rat pinealocytes. The physiological role of the transporter in the termination of the glutamate signal in the pineal gland is discussed.

Original languageEnglish
Pages (from-to)1491-1498
Number of pages8
JournalJournal of Neurochemistry
Volume69
Issue number4
Publication statusPublished - Oct 1 1997

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Keywords

  • Endocrine cell
  • GLT-1
  • L- glutamate
  • Microvesicle
  • Na-dependent glutamate transporter
  • Pineal gland
  • Pinealocyte
  • Reuptake

ASJC Scopus subject areas

  • Biochemistry
  • Cellular and Molecular Neuroscience

Cite this

Yamada, H., Yatsushiro, S., Yamamoto, A., Hayashi, M., Nishi, T., Futai, M., Yamaguchi, A., & Moriyama, Y. (1997). Functional expression of a GLT-1 type Na+-dependent glutamate transporter in rat pinealocytes. Journal of Neurochemistry, 69(4), 1491-1498.