Cell density inversely regulates D- and L-aspartate levels in rat pheochromocytoma MPT1 cells.
In a previous report (FEBS Lett. 434 (1998) 231), we demonstrated for the first time that D-aspartate (D-Asp) is synthesized in rat pheochromocytoma 12 (PC12) cells. This unique amino acid is believed to act as a novel messenger in mammalian cell regulation. However, the dynamics of D-Asp homeostasis in mammalian cells is yet to be elucidated. In this communication, we demonstrate that D-Asp is also synthesized in MPT1 cells (a subclone of PC12 cells) and that the D- and L-Asp levels in cells are regulated by cell density of the culture. Our data show that D-Asp levels increase, while in contrast, L-Asp levels decrease as a function of increased cell density. Conversely, in PC12 cells, which do not express the glutamate transporter involved in the incorporation of D- and L-Asp into cells, L-Asp levels decrease upon cell density increase while D-Asp concentrations remain almost unchanged. The results indicate that the biochemical behaviors of D- and L-Asp in mammalian cells are distinct and that the cellular levels of these stereoisomers appear to be under different control mechanisms.
School of Pharmaceutical Sciences, Kitasato University, Tokyo, Japan.
Zhiqun
Z
Long
Masae
M
Sekine
Minako
M
Adachi
Takemitsu
T
Furuchi
Kazuhiro
K
Imai
Noriyuki
N
Nimura
Hiroshi
H
Homma
D000818:Animals; D001224:Aspartic Acid / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D002452:Cell Count; D006706:Homeostasis; D016716:PC12 Cells; D010673:Pheochromocytoma / Q000378:metabolism* / Q000473:pathology; D051381:Rats; D013237:Stereoisomerism
D001224:Aspartic Acid