Ionotropic glutamate receptors trigger microvesicle-mediated exocytosis of L-glutamate in rat pinealocytes

Shouki Yatsushiro, Hiroshi Yamada, Mitsuko Hayashi, Akitsugu Yamamoto, Yoshinori Moriyama

Research output: Contribution to journalArticle

22 Citations (Scopus)

Abstract

Rat pinealocytes receive noradrenergic innervation that stimulates melatonin synthesis. Besides melatonin, we showed previously that pinealocytes accumulate L-glutamate in microvesicles and secrete it through an exocytic mechanism. The secreted glutamate binds to the class II metabotropic glutamate receptor and inhibits norepinephrine-stimulated melatonin synthesis in neighboring pinealocytes through an inhibitory cyclic AMP cascade. In this study, it was found that, in addition to metabotropic receptors, pinealocytes express functional ionotropic receptors. RT-PCR and northern analyses indicated the expression of mRNA for GluR1, KA2, and NR2C in pineal gland. The presence of GluR1 protein was confirmed by immunological techniques, but neither KA2 nor NR2C was detected. Consistent with this observation, the presence of (RS)-α-amino-3-hydroxy-5-methyl-4- isoxazolepropionic acid or kainate, non-N-methyl-D-aspartate receptor agonists, transiently stimulated increased the intracellular Ca2+ concentration of cultured pinealocytes, whereas N-methyl-D-aspartate did not. These responses were prevented by 6-cyano-7-nitroquinoxaline-2,3-dione, a selective antagonist for non-N-methyl-D-aspartate receptors, by L-type Ca2+ channel blockers such as nifedipine, or by omitting Ca2+ or Na+ in the medium. In the presence of Ca2+ and Na+, (RS)-α-amino-3-hydroxy-5-methyl- 4-isoxazolepropionic acid or kainate evoked glutamate secretion from the cultured cells, which was prevented by 6-cyano-7-nitroquinoxaline-2,3-dione, L-type Ca2+ channel blockers, type E or B botulinum neurotoxin, or incubation at <20°C. These results strongly suggest that GluR1 is functionally expressed in pinealocytes and triggers microvesicle-mediated exocytosis of L-glutamate via activation of L-type Ca2+ channels. It is possible that GluR1 participates in a signaling cascade that enhances and expands the L-glutamate signal throughout the pineal gland.

Original languageEnglish
Pages (from-to)288-297
Number of pages10
JournalJournal of Neurochemistry
Volume75
Issue number1
DOIs
Publication statusPublished - 2000

Keywords

  • Exocytosis
  • Ionotropic glutamate receptor
  • L-Glutamate
  • L-type Ca channel
  • Pinealocytes
  • Synaptic-like microvesicle

ASJC Scopus subject areas

  • Biochemistry
  • Cellular and Molecular Neuroscience

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