Solubilization of multiple binding sites for the dopamine receptor from calf striatal membranes

Specific dopamine binding sites from calf striatum were solubilized using potassium chloride. The solubilized salt extract was found to have the same properties as the native membrane preparation, including binding affinity and stereoselectivity. The binding site required the presence of potassium chloride for solubilization, but not for the maintenance of binding. Multiple binding sites were detected in the potassium chloride extract. Hill coefficients for selected agonists and antagonists using three different ligands which interact with the dopamine receptor, ([3H]spiroperidol, [3H]-2-amino-oJ-dihy-droxy 1,2,3,4-tetrahydronapthalene (ADTN) and [3H]-N-propylnorapomorphine, revealed the presence of more than one population of agonist binding sites. In addition, gel filtration chromatography on Sephacryl S-200 demonstrated three peaks of stereospecific [3H]spiroperidol binding. Similar results were obtained following gel filtration chromatography of the potassium chloride extract on Sephadex G-100. The predominant specific site which was labeled by [3H]apomorphine, [3H]ADTN and [3H]spiroperidol on this column had a calculated molecular weight of about 50,000, as calibrated for globular proteins. These data confirm the existence of multiple binding sites for the dopamine receptor in the central nervous system.