ANGIOTENSIN-II TYPE-2 (AT(2)) RECEPTOR-MEDIATED INHIBITION OF NMDA RECEPTOR SIGNALING IN NEURONAL CELLS

The N-methyl-D-aspartate (NMDA) receptor has been reported to be impor tant in synaptic plasticity, neuronal development, normal brain functi on 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 par amagnetic resonance (EPR) spectroscopy, when challenged with NMDA [Nor by, S.W., Weyhenmeyer, J.A. and Clarkson, R.B., Stimulation and inhibi tion of NO production in macrophages and neuronal cells as observed by spin trapping, Free Rad. Biol. Med., 22 (1997) 1-9]. In the present s tudy, we provide immunochemical evidence for the expression of both th e NMDAR1 and NMDAR2A/B receptor subunits in PC12W cells, that express only the angiotensin type-2 (AT(2)) receptor subtype, and in NG108-15 (NG108) cells, a murine neuroblastoma X glioma hybrid that expresses b oth the angiotensin type-1 (AT(1)) and AT(2) receptor subtypes. We als o show that treatment of PC12W cells with angiotensin (Ang II) decreas es NMDA-induced NO release by 28.0 +/- 4.2%, and that this response ca n be attenuated by pre-treating the cells with the isoform-specific AT (2) antagonist, PD 123319. Interestingly, there was no effect on cGMP accumulation in PC12W cells treated with NMDA. Similar experiments wer e carried out using NG108 cells since the binding properties and funct ional characteristics of their NMDA receptors have been previously des cribed [Ohkuma, S., Katsura, M., Chen, D., Chen, S. and Kuriyama, K., Presence of N-methyl-D-aspartate (NMDA) receptors in neuroblastoma X g lioma hybrid NG 108-15 cells-analysis using Ca-45(2+) influx and [H-3] MK-801 binding as functional measures, Mel. Brain Res. 22 (1994) 166-1 72]. Our results show that NG108 cells significantly increase cGMP lev els 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 AT(2) antagonist, PD 123319, but was not significantly changed by the addition of the AT (1) antagonist, losartan. Further, Ang II action on NMDA signalling in NG108 cells was completely inhibited by the addition of both the AT(1 ) and AT(2) antagonists. Taken together, these results suggest that An gII inhibits NMDA-mediated NO and cGMP production through a mechanism involving the AT(2) receptor subtype.