Synaptic-like microvesicles, synaptic vesicle counterparts in endocrine cells, are involved in a novel regulatory mechanism for the synthesis and secretion of hormones.
Microvesicles 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.
Moriyama
Y
Y
Department of Biochemistry, Faculty of Pharmaceutical Sciences, Okayama University, Okayama 700-8530, Japan. moriyama@pheasant.pharm.okayama-u.ac.jp.
Hayashi
M
M
Yamada
H
H
Yatsushiro
S
S
Ishio
S
S
Yamamoto
A
A
D018698:Glutamic Acid / Q000378:metabolism; D008550:Melatonin / Q000096:biosynthesis* / Q000378:metabolism; D015388:Organelles / Q000201:enzymology / Q000502:physiology*; D010870:Pineal Gland / Q000378:metabolism / Q000648:ultrastructure*; D006180:Proton-Translocating ATPases / Q000378:metabolism; D015398:Signal Transduction; D013572:Synaptic Vesicles; D025262:Vacuolar Proton-Translocating ATPases
D018698:Glutamic Acid; D025262:Vacuolar Proton-Translocating ATPases; D006180:Proton-Translocating ATPases; D008550:Melatonin