Comparison of centrifugation and filtration assays of ligand binding: Do multiple GABA receptive sites exist?

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Abstract
Filtration and microcentrifugation procedures for the separation of bound and free ligand are compared for the assay of GABA receptors. The 3H-GABA and 3H-muscimol are employed as ligands in saturation analyses of SPM and JC preparations. A direct comparison of the two methods, applied to two membrane preparations and two ligands, reveals that nonspecific binding is consistently higher with the microcentrifugation procedure. Analysis of the binding data yields essentially the same constants in either case; however, the filtration assay provides a better estimate in all cases.