Antihistamine terfenadine inhibits calcium influx, cGMP formation, and NMDA receptor-dependent neurotoxicity following activation of L-type voltage sensitive calcium channels

We have investigated the actions of the H1 receptor antagonist terfenadine on voltage sensitive calcium channels and calcium-mediated pathways. We found that terfenadine prevented N-methyl-D-aspartate (NMDA)-mediated excitotoxicity following stimulation of L-type voltage sensitive calcium channels by the specific agonist BayK8644. The neuroprotective effect of terfenadine was concentration-dependent, 10 and 100 nM terfenadine providing 50 and 100% neuroprotection, respectively. Neuroprotection was associated with a decrease in calcium influx via L-voltage sensitive calcium channels. Terfenadine fully reversed the increase in intracellular calcium induced by BayK8644, and delayed significantly the time necessary for this agonist to induce maximum intracellular calcium levels. Calcium-mediated biochemical pathways coupled to voltage sensitive calcium channels activation were also affected by terfenadine. This drug inhibited intracellular cGMP formation by BayK8644 in a concentration-dependent manner, 100 nM terfenadine reducing cGMP formation by 50% and 1 μM terfenadine fully inhibiting cGMP synthesis. Terfenadine reduced NMDA receptor-mediated cGMP formation due to the release of glutamate following activation of calcium channels by BayK8644. Finally, we also show that terfenadine effectively reduced steady-state concentrations of both intracellular calcium and cGMP in unstimulated cultures in their usual growing conditions.