A rapid filtration assay for soluble receptors using polyethylenimine-treated filters

Ligand bound to detergent-solubilized or cytosolic receptors can be separated from free ligand by filtration through glass-fiber filters which have been pretreated with polyethylenimine (PEI). Receptors which can be assayed by this technique include detergent-solubilized muscarinic, adenosine A1, alpha 1-adrenergic, alpha 2-adrenergic, beta-adrenergic, dopamine D2, opiate, bradykinin, and benzodiazepine receptors as well as naturally soluble estradiol receptors. For muscarinic, adenosine, alpha 2, dopamine, and estradiol receptors, specific binding measured by the PEI-filter technique was 84-110% of specific binding measured by gel filtration, demonstrating that the technique gave almost quantitative recovery of bound ligand.