Spermine modulation of specific [3H]‐gabapentin binding to the detergent‐solubilized porcine cerebral cortex α2δ calcium channel subunit

Recent studies have identified the [3H]‐gabapentin‐binding protein, purified from porcine cerebral cortical membranes, as the α2δ subunit of voltage‐sensitive calcium channels (Gee et al., 1996). The present study investigates the influence of the polyamine spermine on specific [3H]‐gabapentin binding to detergent‐solubilized porcine cerebral cortical membranes. Spermine, spermidine, 1,10 diaminodecane, Mg2+ and Zn2+, all divalent cations, displaced [3H]‐gabapentin binding to detergent‐solubilized membranes in a concentration‐dependent manner with a maximal inhibition of 65–75%. Radioligand binding studies showed that spermine did not directly interact with the [3H]‐gabapentin‐binding site. Spermine inhibited [3H]‐gabapentin binding by interacting with a polyamine‐sensitive allosteric site on the membrane protein. The steep concentration‐dependence of spermine inhibition of [3H]‐gabapentin binding may suggest multi‐site co‐operativity. Prolonged dialysis of cerebral cortical membranes and Tween 20‐solubilized membranes resulted in a >2.0 fold increase in [3H]‐gabapentin binding. The increase in binding was due to the removal of a heat stable, low molecular weight (