The increase in angiotensin type-2 receptor mRNA level by glutamate stimulation in cultured rat cortical cells

The changes in the angiotensin type-2 (AT2) receptor mRNA level during glutamate neurotoxicity in cultured rat cortical cells are examined to assess the possible involvement of AT2 receptor in cell injury. The day 10–14 cortical neurons were exposed to glutamate at a toxic concentration of 100 μM for 15 min. The viability of the culture was reduced by 60% after 24 h. AT2 receptor mRNA was then increased 2-fold after exposure to glutamate, while the maximum increase was observed in a dose-dependent manner (50–1000 μM) 3 h after glutamate stimulation. AT2 receptor binding also increased 3–12 h after glutamate exposure. The results suggest that the increase in the AT2 receptor preceded to some extent the insult of the cell after exposure. The increase in the mRNA level was suppressed by MK-801, N-methyl-d-aspartate (NMDA) receptor antagonist, thus indicating the possible involvement of NMDA receptor. The increase in the mRNA level was also antagonized by N-nitro l-arginine methyl-ester, a nitric oxide synthase inhibitor. The hemoglobin, a nitric oxide trap, inhibited the increase in the mRNA level. These results suggest that the increase in the mRNA level is associated with the nitric oxide synthesis by glutamate exposure. The viability of cortical cells after glutamate stimulation was partially restored by the AT2 receptor antagonist and by the antisense oligonucleotide for the AT2 receptor. The present results thus suggest that the AT2 receptor may in some way be related to one of the processes in cell injury caused by glutamate.