Carbamazepine inhibits L-type Ca2+ channels in cultured rat hippocampal neurons stimulated with glutamate receptor agonists.

In order to better understand the mechanism(s) of action of carbamazepine (CBZ), we studied its effects on the increase in [Ca2+]i and [Na+]i stimulated by glutamate ionotropic receptor agonists, in cultured rat hippocampal neurons, as followed by indo- or SBFI fluorescence, respectively. CBZ inhibited the increase in [Ca2+]i stimulated either by glutamate, kainate, alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA), or N-methyl-D-aspartate (NMDA), in a concentration-dependent manner. In order to discriminate the effects of CBZ on the activation of glutamate receptors from possible effects on Ca2+ channels, we determined the inhibitory effects of Ca2+ channel blockers on [Ca2+]i changes in the absence or in the presence of CBZ. The presence of 1 microM nitrendipine, 0.5 microM omega-conotoxin GVIA (omega-CgTx GVIA), or of both blockers, inhibited the kainate-stimulated increase in [Ca2+]i by 51.6, 32.9 or 68.7%, respectively. In the presence of both 100 microM CBZ and nitrendipine, the inhibition was similar (54.1%) to that obtained with nitrendipine alone, but in the presence of both CBZ and omega-CgTx GVIA, the inhibition was greater (54%) than that caused by omega-CgTx GVIA alone. However, CBZ did not inhibit the increase in [Na+]i stimulated by the glutamate receptor agonists, but inhibited the increase in [Na+]i due to veratridine. Tetrodotoxin, or MK-801, did not inhibit the influx of Na+ stimulated by kainate, indicating that Na+ influx occurs mainly through the glutamate ionotropic non-NMDA receptors. Moreover, LY 303070, a specific AMPA receptor antagonist, inhibited the [Na+]i response to kainate or AMPA by about 70 or 80%, respectively, suggesting that AMPA receptors are mainly involved. Taken together, the results suggest that CBZ inhibits L-type Ca2+ channels and Na+ channels, but does not inhibit activation of glutamate ionotropic receptors.