Pharmacological disruption of calcium channel trafficking by the α 2 δ ligand gabapentin

• Published in: Proceedings of the National Academy of Sciences - PNAS 2008-03, Vol.105 (9), p.3628-3633
• Main Authors: Hendrich, Jan, Van Minh, Alexandra Tran, Heblich, Fay, Nieto-Rostro, Manuela, Watschinger, Katrin, Striessnig, Jörg, Wratten, Jack, Davies, Anthony, Dolphin, Annette C.
• Format: Article
• Language: English
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0708930105

The mechanism of action of the antiepileptic and antinociceptive drugs of the gabapentinoid family has remained poorly understood. Gabapentin (GBP) binds to an exofacial epitope of the α 2 δ-1 and α 2 δ-2 auxiliary subunits of voltage-gated calcium channels, but acute inhibition of calcium currents by GBP is either very minor or absent. We formulated the hypothesis that GBP impairs the ability of α 2 δ subunits to enhance voltage-gated Ca 2+ channel plasma membrane density by means of an effect on trafficking. Our results conclusively demonstrate that GBP inhibits calcium currents, mimicking a lack of α 2 δ only when applied chronically, but not acutely, both in heterologous expression systems and in dorsal root-ganglion neurons. GBP acts primarily at an intracellular location, requiring uptake, because the effect of chronically applied GBP is blocked by an inhibitor of the system-L neutral amino acid transporters and enhanced by coexpression of a transporter. However, it is mediated by α 2 δ subunits, being prevented by mutations in either α 2 δ-1 or α 2 δ-2 that abolish GBP binding, and is not observed for α 2 δ-3, which does not bind GBP. Furthermore, the trafficking of α 2 δ-2 and Ca V 2 channels is disrupted both by GBP and by the mutation in α 2 δ-2, which prevents GBP binding, and we find that GBP reduces cell-surface expression of α 2 δ-2 and Ca V 2.1 subunits. Our evidence indicates that GBP may act chronically by displacing an endogenous ligand that is normally a positive modulator of α 2 δ subunit function, thereby impairing the trafficking function of the α 2 δ subunits to which it binds.