The α2δ Ligand Gabapentin Inhibits the Rab11-Dependent Recycling of the Calcium Channel Subunit α2δ-2

The alpha(2)delta subunits of voltage-gated calcium channels are important modulatory subunits that enhance calcium currents and may also have other roles in synaptogenesis. The antiepileptic and antiallodynic drug gabapentin (GBP) binds to the alpha(2)delta-1 and alpha(2)delta-2 isoforms of this protein, and its binding may disrupt the binding of an endogenous ligand, required for their correct function. We have shown previously that GBP produces a chronic inhibitory effect on calcium currents by causing a reduction in the total number of alpha(2)delta and alpha(1) subunits at the cell surface. This action of GBP is likely to be attributable to a disruption of the trafficking of alpha(2)delta subunits, either to or from the plasma membrane. We studied the effect of GBP on the internalization of, and insertion into the plasma membrane of alpha(2)delta-2 using an alpha-bungarotoxin binding site-tagged alpha(2)delta-2 subunit, and a fluorescent derivative of alpha-bungarotoxin. We found that GBP specifically disrupts the insertion of alpha(2)delta-2 from post-Golgi compartments to the plasma membrane, and this effect was prevented by a mutation of alpha(2)delta-2 that abolishes its binding to GBP. The coexpression of the GDP-bound Rab11 S25N mutant prevented the GBP-induced decrease in alpha(2)delta-2 cell surface levels, both in cell lines and in primary neurons, and the GBP-induced reduction in calcium channel currents. In contrast, the internalization of alpha(2)delta-2 was unaffected by GBP. We conclude that GBP acts by preventing the recycling of alpha(2)delta-2 from Rab11-positive recycling endosomes to the plasma membrane.