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Functional Expression of a GLT‐1 Type Na + ‐Dependent Glutamate Transporter in Rat Pinealocytes
Author(s) -
Yamada Hiroshi,
Yatsushiro Shouki,
Yamamoto Akitsugu,
Hayashi Mitsuko,
Nishi Tsuyoshi,
Futai Masamitsu,
Yamaguchi Akihito,
Moriyama Yoshinori
Publication year - 1997
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1997.69041491.x
Subject(s) - pinealocyte , glutamate aspartate transporter , glutamate receptor , biology , extracellular , biochemistry , norepinephrine transporter , excitotoxicity , pineal gland , microbiology and biotechnology , metabotropic glutamate receptor , chemistry , transporter , endocrinology , melatonin , receptor , gene
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 [ 3 H]‐glutamate uptake by cultured pinealocytes was driven by extracellular Na + , saturated with the [ 3 H]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.