Gabapentin Blocks L-Type and P/Q-Type Ca2+ Channels Involved in Depolarization-Stimulated Nitric Oxide Synthase Activity in Primary Cultures of Neurons from Mouse Cerebral Cortex

Purpose: The effect of gabapentin [1-(aminomethyl)cyclohexane acetic acid] on Ca²⁺ channels involving the activation of nitric oxide synthase (NOS) was investigated in primary neuronal culture of mouse cerebral cortex.Methods:The expression of ₂ subunits of Ca²⁺ channels was investigated by RT-PCR using specific primer sets. The K⁺-evoked NOS activity was estimated by guanosine 3'5' cyclic monophosphate (cGMP) formation.Results:mRNA for ₂ subunits of Ca²⁺ channels is found in these cells. Gabapentin blocked the K⁺-evoked NOS activity estimated from cGMP formation in a concentration dependent manner. The increase in NOS activity by the K⁺-stimulation was almost completely reversed by the combination of nifedipine, an L-type Ca²⁺ channel blocker, and -conotoxin GVIA, an N-type Ca²⁺ channel blocker, was failed to reverse the increase in NOS activity by the K⁺-stimulation, indicating that the activation of NOS by the depolarizing stimulation might be not mediated by N-type Ca²⁺ channel. Under the presence of nifedipine or -agatoxin IVA, gabapentin inhibited the increase in NOS activity concentration-dependently.Conclusions: These results suggest that gabapentin inhibits depolarization-induced NOS activation in murine cortical neuronal culture via blockade of both P/Q-type and L-type Ca²⁺ channels.