The Company of Biologists LimitedActa Medica Okayama0022-094920312001Synaptic-like microvesicles, synaptic vesicle counterparts in endocrine cells, are involved in a novel regulatory mechanism for the synthesis and secretion of hormones117125ENYoshinoriMoriyamaMitsukoHayashiHiroshiYamadaShoukiYatsushiroShougoIshioAkitsuguYamamotoMicrovesicles in endocrine cells are the morphological and functional equivalent of neuronal synaptic vesicles. Microvesicles accumulate various neurotransmitters through a transmitter-specific vesicular transporter energized by vacuolar H+-ATPase. We found that mammalian pinealocytes, endocrine cells that synthesize and secrete melatonin, accumulate L-glutamate in their microvesicles and secrete it through exocytosis. Pinealocytes use L-glutamate as either a paracrine- or autocrine-like chemical transmitter in a receptor-mediated manner, resulting in inhibition of melatonin synthesis. In this article, we briefly describe the overall features of the microvesicle-mediated signal-transduction mechanism in the pineal gland and discuss the important role of acidic organelles in a novel regulatory mechanism for hormonal synthesis and secretion.No potential conflict of interest relevant to this article was reported.European Molecular Biology OrganizationActa Medica Okayama0261-418925182006Secretion of L-glutamate from osteoclasts through transcytosis41754186ENRiyoMorimotoShunsukeUeharaShoukiYatsushiroNarinobuJugeZhaolinHuaShigenoriSenohNorikoEchigoMitsukoHayashiToshihideMizoguchiTadashiNinomiyaNobuyukiUdagawaHiroshiOmoteAkitsuguYamamotoRobert HEdwardsYoshinoriMoriyamaOsteoclasts are involved in the catabolism of the bone matrix and eliminate the resulting degradation products through transcytosis, but the molecular mechanism and regulation of transcytosis remain poorly understood. Upon differentiation, osteoclasts express vesicular glutamate transporter 1 (VGLUT1), which is essential for vesicular storage and subsequent exocytosis of glutamate in neurons. VGLUT1 is localized in transcytotic vesicles and accumulates L-glutamate. Osteoclasts secrete L-glutamate and the bone degradation products upon stimulation with KCl or ATP in a Ca2+-dependent manner. KCl- and ATP-dependent secretion of L-glutamate was absent in osteoclasts prepared from VGLUT1-/- knockout mice. Osteoclasts express mGluR8, a class III metabotropic glutamate receptor. Its stimulation by a specific agonist inhibits secretion of L-glutamate and bone degradation products, whereas its suppression by a specific antagonist stimulates bone resorption. Finally, it was found that VGLUT1-/- mice develop osteoporosis. Thus, in bone-resorbing osteoclasts, L-glutamate and bone degradation products are secreted through transcytosis and the released L-glutamate is involved in autoregulation of transcytosis. Glutamate signaling may play an important role in the bone homeostasis.No potential conflict of interest relevant to this article was reported.Acta Medica Okayama105152008Identification of a vesicular nucleotide transporter56835686ENKeisukeSawadaNorikoEchigoNarinobuJugeTakaakiMiyajiMasatoOtsukaHiroshiOmoteAkitsuguYamamotoYoshinoriMoriyama<p>ATP is a major chemical transmitter in purinergic signal transmission. Before secretion, ATP is stored in secretory vesicles found in purinergic cells. Although the presence of active transport mechanisms for ATP has been postulated for a long time, the proteins responsible for its vesicular accumulation remains unknown. The transporter encoded by the human and mouse SLC17A9 gene, a novel member of an anion transporter family, was predominantly expressed in the brain and adrenal gland. The mouse and bovine counterparts were associated with adrenal chromaffin granules. Proteoliposomes containing purified transporter actively took up ATP, ADP, and GTP by using membrane potential as the driving force. The uptake properties of the reconstituted transporter were similar to that of the ATP uptake by synaptic vesicles and chromaffin granules. Suppression of endogenous SLC17A9 expression in PC12 cells decreased exocytosis of ATP. These findings strongly suggest that SLC17A9 protein is a vesicular nucleotide transporter and should lead to the elucidation of the molecular mechanism of ATP secretion in purinergic signal transmission. </p>No potential conflict of interest relevant to this article was reported.Acta Medica Okayama2045-232242014Identification of a mammalian vesicular polyamine transporterENMikiHiasaTakaakiMiyajiYukaHarunaTomoyaTakeuchiYuikaHaradaSawakoMoriyamaAkitsuguYamamotoHiroshiOmoteYoshinoriMoriyamaSpermine and spermidine act as neuromodulators upon binding to the extracellular site(s) of various ionotropic receptors, such as N-methyl-d-aspartate receptors. To gain access to the receptors, polyamines synthesized in neurons and astrocytes are stored in secretory vesicles and released upon depolarization. Although vesicular storage is mediated in an ATP-dependent, reserpine-sensitive fashion, the transporter responsible for this process remains unknown. SLC18B1 is the fourth member of the SLC18 transporter family, which includes vesicular monoamine transporters and vesicular acetylcholine transporter. Proteoliposomes containing purified human SLC18B1 protein actively transport spermine and spermidine by exchange of H+. SLC18B1 protein is predominantly expressed in the hippocampus and is associated with vesicles in astrocytes. SLC18B1 gene knockdown decreased both SLC18B1 protein and spermine/spermidine contents in astrocytes. These results indicated that SLC18B1 encodes a vesicular polyamine transporter (VPAT).No potential conflict of interest relevant to this article was reported.