title: Competitive binding studies with multiple sites. Effects arising from depletion of the free radioligand.
abstract: Apparently anomalous behaviour arises if a radiolabelled drug and a non-radioactive drug compete for binding to a membrane-bound receptor when (a) there is severe depletion of the radiolabelled drug and (b) the non-radioactive drug binds to a heterogeneous population of binding sites. In extreme cases, binding of the non-radioactive drug to the sites of high affinity can be obscured completely. This phenomenon is illustrated by the binding of carbachol to muscarinic receptors, estimated by inhibition of a radiolabelled antagonist.
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism; D008297:Male; D008954:Models, Biological; D011869:Radioligand Assay / Q000592:standards*; D051381:Rats; D011955:Receptors, Drug / Q000032:analysis*
chemical_list: D011955:Receptors, Drug