[Measurement of radioligand binding to beta-adrenergic and benzodiazepine receptors in the cerebral cortex of the rat. Comparison of filtration and centrifugation technics].

The efficiency of separation of the radioligand receptor complex from the unbound ligand by both rapid filtration and centrifugation is compared for two standard receptor assays in the rat brain: the beta-adrenergic receptor using 3H-dihydroalprenolol and the benzodiazepine receptor using 3H-flunitrazepam. Whereas in beta-adrenergic binding studies both separation procedures yield similar binding data, the apparent binding in the benzodiazepine receptor assay is lower in the filtration experiments as compared to the data obtained by centrifugation, indicating an incomplete retention of the ligand receptor complex by filter. However, in both assays the results of the binding studies are highly dependent on the type of filters used. The following filters were compared: glass fibre filters GE/B and GF/C (Whatman Ltd., Kent, England), membrane filter HAWP (pore size 0.45 micrometer, Millipore Corporation, Bedford, U.S.A.) and glass fibre filters NK I, NK VIII, NK-15-90, NK 13-90, NK 14-120 (all produced by VEB Feinpapierfabrik Neu-Kaliss, G.D.R.). Although a somewhat higher specific binding can be obtained by the membrane filter and several types of the NK filters as compared to the most widely used Whatman GF/C the manifold higher unspecific binding of the radioligand by these filters does not favour their use in ligand assays. Retention as well as unspecific binding of the filter NK VIII is very similar to the Whatman GF/C filter. This new filter seems, therefore, well suited for radioligand studies.