The Novel Anticonvulsant Drug, Gabapentin (Neurontin), Binds to the 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 [ 3 H]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 of 130,000, and was heavily glycosylated. The partial N-terminal amino acid sequence of the M 130,000 polypeptide, EPFPSAVTIK, was identical to that reported for the α subunit of the L-type Ca 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 [ 3 H]gabapentin binding sites were found in membranes prepared from rat brain, heart and skeletal muscle. Binding of [ 3 H]gabapentin to COS-7 cells transfected with α cDNA was elevated >10-fold over controls, consistent with the expression of α protein, as measured by Western blotting. Finally, purified L-type Ca channel complexes were fractionated, under dissociating conditions, on an ion-exchange column; [ 3 H]gabapentin binding activity closely followed the elution of the α subunit. [ 3 H]Gabapentin is the first pharmacological agent described that interacts with an α subunit of a voltage-dependent Ca channel.