Binding of [3H]SKF 38393 to Dopamine D‐l Receptors in Rat Striatum In Vitro; Estimation of Receptor Molecular Size by Radiation Inactivation

Abstract: [3H]SKF 38393 (2,3,4,5,-tetrahydro-7,8-dihy-droxy-l-phenyl-lH-3-benzazepine) binds with high affinity to 3,4-dihydroxyphenylethylamine (dopamine) D-l receptors in rat striatum in vitro (KD= 7 and 14 nM in nonfrozen and frozen striatum, respectively). The number of binding sites (5max) was ∼ 80.0 pmol/g of original tissue, a value similar to the Bmax for the dopamine D-l antagonist SCH 23390. Nondisplaceable [3H]SKF 38393 binding was ∼45% of total binding. Irradiation (0–4 Mrad) of frozen whole striata decreased the number of [3H]SKF 38393 binding sites monoexponentially without changing the binding affinity. The functional molecular mass for the agonist dopamine D-1 binding site was 132,800 daltons, which is higher than the functional molecular mass of the antagonist dopamine D-1 binding site (∼80,000 daltons).