The novel anticonvulsant drug, gabapentin (Neurontin), binds to the alpha(2)delta subunit of a calcium channel

Gabapentin (1-(aminomethyl)cyclohexane acetic acid; Neurontin) is a novel anticonvulsant drug, with a mechanism of action apparently dissimilar to that of other antiepileptic agents. We report here the isolation and characterization of a [H-3]gabapentin binding protein from pig cerebral cortex membranes. The detergent-solubilized binding protein was purified 1022-fold, in a six-step column-chromatographic procedure, with a yield of 3.9%. The purified protein had an apparent subunit M(r) of 130,000, and was heavily glycosylated. The partial N-terminal amino acid sequence of the M(r) 130,000 polypeptide, EPFPSAVTIK, was identical to that reported for the alpha(2) delta subunit of the L-type Ca2+ channel from rabbit skeletal muscle (Hamilton, S. L., Hawkes, M. J., Brush, K., Cook, R., Chang, R. J., and Smilowitz, H. M. (1989) Biochemistry 28, 7820-7828). High levels of [H-3]gabapentin binding sites were found in membranes prepared from rat brain, heart and skeletal muscle. Binding of [H-3]gabapentin to COS-7 cells transfected with alpha(2) delta cDNA was elevated >10-fold over controls, consistent with the expression of alpha(2) delta protein, as measured by Western blotting. Finally, purified L-type Ca2+ channel complexes were fractionated, under dissociating conditions, on an ion-exchange column; [H-3]gabapentin binding activity closely followed the elution of the alpha(2) delta subunit. [H-3]Gabapentin is the first pharmacological agent described that interacts with an alpha(2) delta subunit of a voltage-dependent Ca2+ channel.