Solubilization and Characterization of a [³H]Hemicholinium‐3 Binding Site in Rat Brain

Abstract: A sodium‐dependent high‐affinity [³H]‐hemicholinium‐3 ([³H]HCh‐3) binding site was solubilized from rat striatal synaptic plasma membranes by 0.2% deoxycholate. Deoxycholate solubilization of the [³H]HCh‐3 binding site was dependent upon both detergent concentration and ionic strength of the solubilization medium. Specific [³H]HCh‐3 binding to the solubilized preparation was both sodium‐ and chloride‐dependent and saturable, exhibiting an affinity of 14.2 nM and a capacity (B_max) of 695 fmol/mg protein. Choline and other analogs inhibited specific [³H]HCh‐3 binding to the solubilized preparation in a concentration‐dependent manner with the similar rank order of potency observed in crude synaptic membranes. Treatments known to disrupt both protein and lipid moieties resulted in diminished specific [³H]HCh‐3 binding. These results suggest that the characteristics of the solubilized [³H]HCh‐3 binding site are similar to those of the membrane‐bound site.