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

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 (Bmax) 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.