Gabapentin inhibits high-threshold calcium channel currents in cultured rat dorsal root ganglion neurones

Abstract

1. This study examined the action of gabapentin (gabapentin, 1-(aminomethyl) cyclohexane acetic acid (Neurontin®)) on voltage-gated calcium (Ca2+) channel influx recorded in cultured rat dorsal root ganglion (DRG) neurones. 2. Voltage-gated Ca2+ influx was monitored using both fura-2 based fluorescence Ca2+ imaging and the whole-cell patch clamp technique. 3. Imaging of intracellular Ca2+ transients revealed that gabapentin inhibited KCl (30 mM)-evoked voltage-dependent Ca2+ influx. Both the duration for 50% of the maximum response (W50) and total Ca2+ influx were significantly reduced by ∼25-30% in the presence of gabapentin (25 μM). 4. Gabapentin potently inhibited the peak whole-cell Ca2+ channel current (IBa) in a dose-dependent manner with an estimated IC50 value of 167 nM. Block was incomplete and saturated at a maximal concentration of 25 μM. 5. Inhibition was significantly decreased in the presence of the neutral amino acid L-isoleucine (25 μM) but unaffected by application of the GABAB antagonist, saclofen (200 μM), suggesting a direct action on the α2δ subunit of the Ca2+ channel. 6. Gabapentin inhibition was voltage-dependent, producing an ∼7 mV hyperpolarizing shift in current voltage properties and reducing a non-inactivating component of whole-cell current activated at relatively depolarized potentials. 7. The use of specific Ca2+ channel antagonists revealed a mixed pharmacology of the gabapentinsensitive current (N-, L- and P/Q-type), which is dominated by N-type current. 8. The present study is the first to demonstrate that gabapentin directly mediates inhibition of voltage-gated Ca2+ influx in DRG neurones, providing a potential means for gabapentin to effectively mediate spinal anti-nociception.