Biol. Pharm. Bull. 29(3) 547—549 (2006)

L-Glutamate, an excitatory amino acid, acts as an intercellular transmitter in the central nervous system and some peripheral tissues. For L-glutamate signal transmission, Lglutamate is stored in secretory vesicles and then secreted from the cells through exocytosis. Vesicular glutamate transporter (VGLUT) is responsible for the vesicular storage of Lglutamate through an active transport mechanism, and plays a central role in glutamatergic signal transmission. In 2000, the VGLUT1 moiety was identified. Successively, two VGLUT1 isoforms, VGLUT2 and 3, were identified. Molecular biological studies on VGLUT1 gene disruption further demonstrated the essential role of VGLUT in L-glutamate signal transmission. Although none of functional difference between VGLUT1 and 2 was identified, complementary expression of two isoforms in glutamatergic neurons in brain suggests distinct roles in signal transmission. Immunohistochemistry of VGLUTs also showed that VGLUT2 is localized in the synapses with high release probability than VGLUT1. On the other hand, VGLUT3 is expressed in GABAergic neurons, cholinergic neurons and serotonergic neurons. Localization of VGLUT3 other than glutamatergic neurons suggest a novel mode of glutamate signaling. However, very little is known about the molecular nature of the VGLUT moiety as well as the molecular mechanism of Lglutamate transport. As the first step to remedy this, in the present study, we investigated the membrane topology of VGLUT2 expressed in COS7 cells by means of immunological techniques.