Differentiation of solubilized dopamine receptors from spirodecanone binding sites in rat striatum.

Solubilization of dopamine receptors, in a native form, was first achieved in our laboratory using dog striatum and the mild detergent digitonin [l-3]. These results were confirmed by another group in both dog and human brain [4f. However, earlier attempts to solubilize dopamine receptors from rat striatum were ~s~essfui~ even though a similar experimental procedure was used [3,5]. Although the binding properties of dopamine receptors in striatal membrane preparations were identical in both animals, the discrepancy between the data from rat and dog remained unexplained [3], This study was undertaken to solve the problem. The results show that the solubilized dopamine receptors from rat striatum are masked by a high number of non-specific but displaceable spiperone binding sites. These binding sites have been already described in membrane preparations as non-stereospecific or spirod~anone sites (cf. Gg.2) [6,7]. The use of a compound which is s~uct~a~y related to spiperone, but is inactive on dopamine receptors enabled us to determine and characterize solubilized dopamine receptors from the rat striatum, by means of the charcoal assay method.