Angiotensin II type-2 (AT2) receptor-mediated inhibition of NMDA receptor signalling in neuronal cells

The N-methyl-D-aspartate (NMDA) receptor has been reported to be important in synaptic plasticity, neuronal development, normal brain function and neurologic disease. We have recently shown that PC12W cells, a subclone of rat pheochromocytoma PC12 cell line, release nitric oxide (NO), as measured by in vitro spin-trapping combined with electron paramagnetic resonance (EPR) spectroscopy, when challenged with NMDA [Norby, S.W., Weyhenmeyer, J.A. and Clarkson, R.B., Stimulation and inhibition of NO production in macrophages and neuronal cells as observed by spin trapping, Free Rad. Biol. Med., 22 (1997) 1-9]. In the present study, we provide immunochemical evidence for the expression of both the NMDAR1 and NMDAR2A/B receptor subunits in PC12W cells, that express only the angiotensin type-2 (AT2) receptor subtype, and in NG108-15 (NG108) cells, a murine neuroblastoma x glioma hybrid that expresses both the angiotensin type-1 (AT1) and AT2 receptor subtypes. We also show that treatment of PC12W cells with angiotensin (Ang II) decreases NMDA-induced NO release by 28.0 +/- 4.2%, and that this response can be attenuated by pre-treating the cells with the isoform-specific AT2 antagonist, PD 123319. Interestingly, there was no effect on cGMP accumulation in PC12W cells treated with NMDA. Similar experiments were carried out using NG108 cells since the binding properties and functional characteristics of their NMDA receptors have been previously described [Ohkuma, S., Katsura, M., Chen, D., Chen, S. and Kuriyama, K., Presence of N-methyl-D-aspartate (NMDA) receptors in neuroblastoma x glioma hybrid NG 108-15 cells-analysis using 45Ca2+ influx and [3H]MK-801 binding as functional measures, Mol. Brain Res. 22 (1994) 166-172]. Our results show that NG108 cells significantly increase cGMP levels when challenged with NMDA (21.2 +/- 5.0% over control levels), and that this response can be attenuated by the addition of angiotensin (57.1 +/- 6.2% of stimulated levels). The effect of angiotensin on NMDA-mediated changes in cGMP levels was blocked by the AT2 antagonist, PD 123319, but was not significantly changed by the addition of the AT1 antagonist, losartan. Further, Ang II action on NMDA signalling in NG108 cells was completely inhibited by the addition of both the AT1 and AT2 antagonists. Taken together, these results suggest that AngII inhibits NMDA-mediated NO and cGMP production through a mechanism involving the AT2 receptor subtype.