L. Dus et al., NMDA RECEPTOR MODULATION BY A CONDITIONED MEDIUM DERIVED FROM RAT CEREBELLAR GRANULE CELLS, European journal of neuroscience, 9(12), 1997, pp. 2668-2676
Our previous studies have shown that the response to the excitotoxic a
ction of glutamate by cultured cerebellar granule cells depends upon t
he cell density or the volume of medium in which they have been grown:
the higher the cell density or the lower the volume, the higher the r
esponse to glutamate. We have hypothesized that this variable response
is due to the formation in culture of a glutamate-sensitizing activit
y GSA more abundantly in conditioned medium derived from high-density
or low-volume cultures than that present in low-density or high volume
cultures and capable of restoring sensitivity in previously resistant
granule cells. In order to elucidate the mechanism of action of gluta
mate-sensitizing activity, we measured the extent and function of NMDA
receptors in low-and high-volume cultures and assessed the effect oi
glutamate-sensitizing activity on the same receptors. We found that un
der high-volume conditions the extent of MK-801 binding, the amount of
NMDA receptor type 1, the currents evoked in whole cells after an NMD
A pulse and the response of cultured cells to this ligand were markedl
y reduced compared with low-volume cultures. Addition of glutamate-sen
sitizing activity to high-volume cultures increased their glutamate se
nsitivity the NMDA-evoked currents, the extent of MK-801 binding and t
he amount of NMDA receptor type 1 protein present. The corresponding m
RNA transcripts, on the contrary, were unchanged in high-volume, low-v
olume and high-volume GSA-treated cultures.