S. Alavez et al., CHARACTERIZATION OF THE ACTIVATION OF GLUTAMINASE INDUCED BY N-METHYL-D-ASPARTATE AND POTASSIUM IN CEREBELLAR GRANULE CELLS, Journal of neuroscience research, 45(5), 1996, pp. 637-646
Chronic stimulation of cerebellar granule cells with N-methyl-D-aspart
ate (NMDA) or KCl induces a specific activation of the enzymes directl
y involved in glutamate neurotransmitter synthesis, Phosphate-activate
d glutaminase (FAG) activity is enhanced in cultured granule neurons i
ncubated with 150 mu M NMDA or 25 mM KCl, Other enzymes are not affect
ed by this treatment like lactate dehydrogenase (LDH) and glutamate de
hydrogenase (GLDH), which is also a mitochondrial enzyme but not direc
tly involved in neurotransmitter synthesis, This effect is dependent o
n protein synthesis and is induced after 12 hr of NMDA or KCl stimulat
ion, Kinetics of FAG activity showed that K-m values were unaffected,
in contrast to V-max values that were increased approximately 70% and
215% over control by NMDA and KCl treatment, respectively, For GLDH, w
e found two isoforms that were affected differentially by the experime
ntal conditions, Western blot analysis clearly evidenced an increase o
f approximately 120-180% in the amount of FAG in NMDA- and KCl-treated
cells, whereas GLDH was not significantly modified, These results dem
onstrate that the NMDA- and KCl-induced activation of FAG are not due
to the modification of the preexisting enzyme, but to an increase in t
he synthesis of this enzyme, This suggests that NMDA receptor stimulat
ion during critical periods of the cerebellar granule cell development
leads to the activation of gene expression involved in the process of
cell differentiation. (C) 1996 Wiley-Liss, Inc.