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

摘要

1 This study examined the action of gabapentin (gabapentin,1-(aminomethyl) cyclohexane acetic acid (Neurontin~(~R))) on voltage-gated calcium (Ca~(2+)) channel influx recorded in cultured rat dorsal root ganglion (DRG) neurones. 2 Voltage-gated Ca~(2+) influx was monitored using both fura-2 based fluorescence Ca~(2+) imaging and the whole-cell patch clamp technique. 3 Imaging of intracellular Ca~(2+) transients revealed that gabapentin inhibited KCl (30 mM)-evoked voltage-dependent Ca~(2+) influx. Both the duration for 50% of the maximum response (W50) and total Ca~(2+) influx were significantly reduced by ～25-30% in the presence of gabapentin (25 μM). 4 Gabapentin potently inhibited the peak whole-cell Ca~(2+) channel current (I_(Ba)) in a dose-dependent manner with an estimated IC_(50) 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 GABA_B antagonist, saclofen (200 μM), suggesting a direct action on the α_2δ subunit of the Ca~(2+) 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 Ca~(2+) channel antagonists revealed a mixed pharmacology of the gabapentin- sensitive 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 Ca~(2+) influx in DRG neurones, providing a potential means for gabapentin to effectively mediate spinal anti-nociception.