Gabapentin inhibits high-threshold calcium channel currents in cultured rat dorsal root ganglion neurones.
1. This study examined the action of gabapentin (gabapentin,1-(aminomethyl) cyclohexane acetic acid (Neurontin) 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 approximately 25-30% in the presence of gabapentin (25 microM). 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 microM. 5. Inhibition was significantly decreased in the presence of the neutral amino acid L-isoleucine (25 microM) but unaffected by application of the GABA(B) antagonist, saclofen (200 microM), suggesting a direct action on the alpha(2)delta subunit of the Ca(2+) channel. 6. Gabapentin inhibition was voltage-dependent, producing an approximately 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.
Sutton
K G
KG
Department of Biology, Pfizer Global R&D, Cambridge Laboratories, Cambridge, CB2 2QB. Kathy_sutton@merck.com
Martin
D J
DJ
Pinnock
R D
RD
Lee
K
K
Scott
R H
RH
D000085:Acetates / Q000494:pharmacology*; D000588:Amines; D000818:Animals; D000927:Anticonvulsants / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology*; D002478:Cells, Cultured; D003509:Cyclohexanecarboxylic Acids; D004305:Dose-Response Relationship, Drug; D000077206:Gabapentin; D005727:Ganglia, Spinal / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D005680:gamma-Aminobutyric Acid
D000085:Acetates; D000588:Amines; D000927:Anticonvulsants; D015220:Calcium Channels; D003509:Cyclohexanecarboxylic Acids; D005680:gamma-Aminobutyric Acid; D000077206:Gabapentin; D002118:Calcium