Alternative splicing of the Ca2+ channel β4 subunit confers specificity for gabapentin inhibition of Cav2.1 trafficking

Gabapentin is well established as an effective treatment for neuropathic pain; however, little is known about its mechanism of action. It binds with high affinity to Ca2+ channel alpha 2 delta subunits that are expressed in dorsal root ganglia. Mutation of a single alpha 2 delta amino acid, R217A, eliminates both gabapentin binding and analgesic efficacy. Gabapentin does not seem to have direct Ca2+ channel blocking properties but does affect overall levels of Ca2+ channel surface expression in some circumstances. In this report, we examined gabapentin effects on trafficking and voltage-dependent gating properties of recombinant Ca(v)2.1 Ca2+ channel complexes transiently expressed in Xenopus laevis oocytes. We also determined electrophysiologically whether gabapentin causes displacement of beta subunits from Ca(v)2.1 complexes. Our principal findings are as follows: 1) gabapentin inhibits trafficking of recombinant Ca(v)2.1 Ca2+ channels in X. laevis oocytes; 2) gabapentin inhibition occurs in the presence of the Ca2+ channel beta 4a subunit but not in the presence of beta 4b; 3) gabapentin does not affect Ca(v)2.1 voltage-dependent gating parameters; 4) inhibition of Ca(v)2.1 trafficking is highly dependent on beta-subunit concentration; and 5) gabapentin inhibition of Ca(v)2.1 trafficking can be reversed by the alpha 2 beta R217A mutation. Overall, our results suggest that gabapentin reduces the number of beta 4a-bound Ca(v)2.1 complexes that are successfully trafficked to the plasma membrane. This mechanism may help to explain why gabapentin is both effective and selective in the treatment of neuropathic pain states that involve up-regulation of alpha 2 beta subunits.