Abstract
AMPA-subtype glutamate receptors (AMPARs), which mediate fast excitatory neurotransmission in most of CNS neurons, are also expressed in glioma cells. To clarify their pathophysiological significance, we used a human glioma cell line U-87MG as a model system. We first examined the expression of AMPAR subunits, GluR1-GluR4, by RT-PCR and immunoblot analyses. This cell line endogenously expressed GluR1, GluR2 and GluR3. Regarding the GluR2 subunit, both the edited form (GluR2R) and unedited form (GluR2Q) were co-expressed in U-87MG cells. Next, we measured AMPA-induced changes in the intracellular Ca2+ concentration using fura-2AM. The application of 100 μM AMPA together with 100 μM cyclothiazide significantly increased the Ca2+ concentration in ~30% of the total cells tested, and this effect was blocked by an AMPAR antagonist NBQX at 40 μM. When GluR2R was overexpressed using adenoviral vectors, no AMPA-induced rise of the intracellular Ca2+ concentration was detected. Furthermore, the GluR2R gene transfer caused retraction of cytoplasmic processes within 4 days after viral infection. These morphological changes did not occur in the presence of 40 μM NBQX in the culture medium. Viability rates significantly decreased in GluR2R-transfered cells, and this was also restored by NBQX. These changes were specific in GluR2R-transferred cells and were never seen when GluR1, GluR3, GluR4 and GluR2Q were transferred. These results indicate that GluR2R plays a critical role in viability and proliferation of U87-MG glioma cells. [Jpn J Physiol 54 Suppl:S81 (2004)]
