Characterization of cholate-solubilized dopamine receptors from human, dog and rat brain

[3H]Spiperone binding sites were solubilized in high yield from human, dog and rat brain with a mixture of sodium cholate (0.3% w/v) and sodium chloride (1.4 M). The binding sites were not sedimented after one hour at 100,000 g, they passed freely through 0.20 micron filters, migrated as a single peak in gradient sedimentation and were retarded upon gel filtration, proving that they were truly solubilized. The solubilized binding sites were definitely of dopaminergic nature. They showed saturable, reversible, high affinity binding of [3H]spiperone; displacement of [3H]spiperone binding by nanomolar concentrations of dopamine antagonists and micromolar concentrations of serotonin antagonists; stereo-specificity and a good correlation with drug affinities for membrane preparations. The non-displaceable, non-specific [3H]spiperone binding was very low. Gradient sedimentation analysis revealed a sedimentation coefficient of 12 S for dog solubilized preparations, 9 S for rat solubilized preparations and only 2.5 S for human solubilized preparations (values, uncorrected for detergent binding). Gel filtration experiments seem to confirm these molecular characteristics. Therefore the present results show that the dopamine receptor reveals the same pharmacological properties when solubilized with cholate-salt from rat, dog or human brain, while physico-chemical properties seem to indicate some differences.