Improvement in Conditions for Solubilisation and Characterisation of Brain D₂ Dopamine Receptors Using Various Detergents

Abstract: A series of detergents of varying chemical properties has been tested for solubilisation of bovine caudate nucleus D₂ dopamine receptors using [³H]spiperone binding to assay the solubilised sites. The properties of the lysophosphatidylcholine (LPC)‐ and 3‐[(3‐cholamidopropyl)dimethylammonio]‐1‐propane‐sulphonate (CHAPS)‐solubilised preparations are described in detail. The preparations are truly solubilised, and sucrose density gradient and gel filtration data are reported. Specific [³H]spiperone binding in the LPC‐solubilised preparation assayed at 4°C is solely to D₂ dopamine re‐ceptors. If the assay temperature is raised to 25°C, the amount of specific [³H]spiperone binding is largely unchanged, but it forms a greater proportion of the total [³H]spiperone binding owing to a reduction in nonstereospecific (spirodecanone) [³H]spiperone binding at the higher temperature. The effect of raising the assay temperature is important as it enables more precise deter‐minations of specific [³H]spiperone binding to be made. Part of the specific [³H]spiperone binding at 25°C is to solubilised S₂ serotonin receptors in addition to D₂ dopamine receptors. Good correlations are observed between the affinities for binding of ligands to the solubilised D₂ receptors and corresponding data obtained on membrane‐bound receptors. Agonist binding in LPC‐solubilised preparations is insensitive to guanine nucleotides. It is speculated that the spirodecanone sites represent, in part, proteolysed or damaged D₂ dopamine, or S₂ serotonin, receptors. In the CHAPS‐solubilised preparation the pharmacological profile of [³H]spiperone binding is unclear when assayed at 4°C, but in assays at 25°C a clear serotonin S₂ receptor component of specific [³H]spiperone binding can be discerned. No clear D₂ dopamine receptor component can be detected in this preparation under these conditions.