Functional characterization of α7 nicotinic acetylcholine and NMDA receptor signaling in SH-SY5Y neuroblastoma cells in an ERK phosphorylation assay

In the present study, the functional properties of alpha 7 nicotinic acetylcholine receptors (alpha 7 nAChRs) and N-methyl-D-aspartate receptors (NMDARs) endogenously expressed in SH-SY5Y human neuroblastoma cells were characterized in an extracellular-signal regulated kinase (ERK) phosphorylation assay. Both choline and N-methyl-D-aspartate (NMDA) mediated robust concentration-dependent increases in ERK phosphorylation in the SH-SY5Y cells, exhibiting EC50 values in good agreement with those reported for the agonists at recombinant alpha 7 nAChRs and NMDARs, respectively. Importantly, the responses evoked by choline (10 mM) and by NMDA (50 mu M) were significantly inhibited by the alpha 7-selective antagonist alpha-bungarotoxin (100 nM) and by the NMDAR-selective antagonist MK-801 (50 mu M), respectively. The increased ERK phosphorylation levels observed upon co-application of choline (1, 3, 10 mM) and NMDA (50 mu M) compared to those produced by the two agonists on their own were fully reconcilable with additive effects and did not reveal substantial synergy between alpha 7 nAChR and NMDAR signaling. Interestingly, however, the responses evoked by the "choline (10 mM) - NMDA (50 mu M)" combination were almost completely inhibited by a-bungarotoxin (100 nM) as well as by MK-801 (50 mu M), suggesting some sort of a link between alpha 7 nAChR- and NMDAR-mediated ERK phosphorylation. Finally, oligomeric amyloid-beta(1-42) peptide (1000 nM) mediated robust inhibition of the ERK phosphorylation induced by choline (10 mM), NMDA (50 mu M) and the "choline (10 mM) - NMDA (50 mu M)" combination. In conclusion, ERK phosphorylation measurements in SH-SY5Y cells provides a robust assay for studies of alpha 7 nAChR-and NMDAR-mediating signaling and putative functional interactions between the receptors.