title: Norepinephrine triggers Ca2+-dependent exocytosis of 5-hydroxytryptamine from rat pinealocytes in culture.
abstract: 5-hydroxytryptamine (5-HT) is a precursor and a putative modulator for melatonin synthesis in mammalian pinealocytes. 5-HT is present in organelles distinct from l-glutamate-containing synaptic-like microvesicles as well as in the cytoplasm of pinealocytes, and is secreted upon stimulation by norepinephrine (NE) to enhance serotonin N-acetyltransferase activity via the 5-HT2 receptor. However, the mechanism underlying the secretion of 5-HT from pinealocytes is unknown. In this study, we show that NE-evoked release of 5-HT is largely dependent on Ca2+ in rat pinealocytes in culture. Omission of Ca2+ from the medium and incubation of pineal cells with EGTA-tetraacetoxymethyl-ester inhibited by 59 and 97% the NE-evoked 5-HT release, respectively. Phenylephrine also triggered the Ca2+-dependent release of 5-HT, which was blocked by phentolamine, an alpha antagonist, but not by propranolol, a beta antagonist. Botulinum neurotoxin type E cleaved 25 kDa synaptosomal-associated protein and inhibited by 50% of the NE-evoked 5-HT release. Bafilomycin A1, an inhibitor of vacuolar H+-ATPase, and reserpine and tetrabenazine, inhibitors of vesicular monoamine transporter, all decreased the storage of vesicular 5-HT followed by inhibition of the NE-evoked 5-HT release. Agents that trigger L-glutamte exocytosis such as acetylcholine did not trigger any Ca2+-dependent 5-HT release. Vice versa neither NE nor phenylephrine caused synaptic-like microvesicle-mediated l-glutamate exocytosis. These results indicated that upon stimulation of a adrenoceptors pinealocytes secrete 5-HT through a Ca2+-dependent exocytotic mechanism, which is distinct from the exocytosis of synaptic-like microvesicles.
authors.affiliation: Department of Biochemistry, Faculty of Pharmaceutical Sciences, Okayama University, Okayama, Japan. hiroyama@md.okayama-u.ac.jp
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yamada
authors.forename: Mitsuko
authors.initials: M
authors.lastname: Hayashi
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Uehara
authors.forename: Mika
authors.initials: M
authors.lastname: Kinoshita
authors.forename: Akiko
authors.initials: A
authors.lastname: Muroyama
authors.forename: Masami
authors.initials: M
authors.lastname: Watanabe
authors.forename: Koji
authors.initials: K
authors.lastname: Takei
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Moriyama
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects; D018698:Glutamic Acid / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D026901:Membrane Transport Proteins; D009479:Neuropeptides; D009638:Norepinephrine / Q000494:pharmacology*; D010870:Pineal Gland / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism; D012110:Reserpine / Q000494:pharmacology; D022142:Secretory Vesicles / Q000378:metabolism; D012701:Serotonin / Q000096:biosynthesis* / Q000378:metabolism; D012702:Serotonin Antagonists / Q000494:pharmacology; D013747:Tetrabenazine / Q000494:pharmacology; D025262:Vacuolar Proton-Translocating ATPases / Q000037:antagonists & inhibitors; D050492:Vesicular Biogenic Amine Transport Proteins; D050493:Vesicular Monoamine Transport Proteins
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D004791:Enzyme Inhibitors; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009479:Neuropeptides; D011942:Receptors, Adrenergic, alpha; D012702:Serotonin Antagonists; D050492:Vesicular Biogenic Amine Transport Proteins; D050493:Vesicular Monoamine Transport Proteins; D012701:Serotonin; D018698:Glutamic Acid; D012110:Reserpine; D025262:Vacuolar Proton-Translocating ATPases; D002118:Calcium; D009638:Norepinephrine; D013747:Tetrabenazine