Interactions between NMDA receptors and mGlu 5 receptors expressed in HEK293 cells

Ca 2+ imaging was used to investigate interactions between responses induced by N ‐methyl‐ D ‐aspartate (NMDA; 15 μ M ) and (RS)‐3,5‐dihydroxyphenyl‐glycine (DHPG; 30 μ M ) in human embryonic kidney (HEK) 293 cells, transiently transfected with rat recombinant NR1a, NR2A and mGlu 5a cDNA. Responses to NMDA were reversibly depressed by DHPG from 244±14 to 194±12% of baseline. Treatment with thapsigargin (1 μ M , 10 min) prevented this effect. After thapsigargin pretreatment, repeated applications of NMDA showed a gradual rundown in amplitude over a period of several hours, and were unaffected by DHPG. Continuous perfusion with staurosporine (0.1 μ M ), after thapsigargin pretreatment, converted the run‐down to a small increase in NMDA responses to 123±6 % of baseline. DHPG induced a further and sustained potentiation of NMDA responses to 174±12% of the initial baseline. The protein tyrosine kinase (PTK) inhibitors genistein (50 μ M ) and 3‐(4‐chlorophenyl)1‐(1,1‐dimethylethyl)‐1 H ‐pyrazolo[3,4‐d]pyrimidin‐4‐amine (PP2; 1 μ M ) inhibited the staurosporine‐ and DHPG‐induced potentiation of NMDA responses. The protein phosphatase (PTP) inhibitors orthovanadate (100 μ M ) and phenyl arsine oxide (PAO, 1 μ M ) facilitated the staurosporine‐evoked potentiation of NMDA responses and occluded DHPG‐induced potentiation. In conclusion, complex interactions can be demonstrated between mGlu 5 and NMDA receptors expressed in HEK293 cells. There is a negative inhibitory influence of Ca 2+ release and PKC activation. Inhibition of these processes reveals a tonic, mGlu 5 receptor and PTK‐dependent potentiation of NMDA receptors that can be augmented by either stimulating mGlu 5 receptors or by inhibiting PTPs.British Journal of Pharmacology (2004) 142 , 991–1001. doi: 10.1038/sj.bjp.0705861