The dihydropyridine nitrendipine modulates N-methyl-D-aspartate receptor channel function in mammalian neurons

Nitrendipine and other dihydropyridine voltage-sensitive calcium channel (VSCC) antagonists have been demonstrated to possess anticonvulsant and neuroprotectant activity in a variety of model systems. Likewise, antagonists of the N-methyl-D-aspartate (NMDA) glutamate receptor subtype act as potent anticonvulsant and neuroprotective agents. Both VSCC and NMDA antagonists exert their effects by inhibiting the neuronal influx of calcium associated with activation of VSCCs or the NMDA receptor, respectively. Although results that provide evidence for crossreactivity between compounds acting at dihydropyridine-sensitive VSCCs and the NMDA receptor-channel complex have been reported, direct modulation of NMDA receptor function by dihydropyridines has not been demonstrated. In the present investigation, we report that nanomolar concentrations of nitrendipine reduced NMDA/glycine-evoked calcium flux and single-channel current in mouse cerebellar granule cell cultures. As measured with the calcium-specific probe indo-1, nitrendipine (0.1-10 microM) attenuated inward calcium flux evoked by bath application of NMDA (100 microM) and glycine (100 microM), in a concentration-dependent (IC50, 0.56 +/- 0.21 microM; 95% confidence interval, 0.19-1.3 microM) and reversible manner. Over a similar concentration range (0.01-100 microM), nitrendipine also inhibited the binding of [3H]MK-801 to mouse cortical and hippocampal membranes (IC50, 0.56 +/- 0.12 microM; 95% confidence interval, 0.37-0.84 microM). Finally, nitrendipine concentration- and voltage-dependently reduced the frequency of NMDA (10 microM)- and glycine (1 microM)-evoked single-channel openings and bursts recorded from excised outside-out patches of mouse cerebellar granule cells. These results indicate that nitrendipine suppresses NMDA/glycine-mediated calcium influx by a rapid and direct interaction with the NMDA receptor-channel complex. Furthermore, these results suggest that the interaction of nitrendipine with the NMDA receptor-channel complex is not tissue specific and probably does not require participation of calcium-dependent second messenger systems. Together, the data presented here support the novel hypothesis that nitrendipine may exhibit anticonvulsant and neuroprotectant activity via the combined ability to modulate both NMDA-associated ion channels and L-type VSCCs.