3H]clonidine and [ 3H]yohimbine binding to solubilized α2-adrenoceptors from rat cerebral cortex

Abstract

α 2-Adrenoceptors were solubilized from rat cerebral cortex using the zwitterionic detergent, 3-[(3- cholamidopropyl)-dimethylammonio]-1-propane sulfonate (CHAPS). The CHAPS extract retained binding activity for [ 3H]clonidine and [ 3H]yohimbine. Treatment of membranes with 10 mM CHAPS solubilized about 30% of the [ 3H]clonidine binding sites in the starting membranes. A Scatchard plot of [ 3H]clonidine binding to the CHAPS extract showed a non-linear curve, indicating the existence of the two distinct binding components. The effects of GTP and cations on α 2-agonist and antagonist binding to the CHAPS extract were similar to the effects in membrane preparations. Sepharose CL-4B column chromatography showed the α 2-agonist binding complex to be a larger molecule, with a Stokes radius of 85 Å, than the α 2-antagonist binding complex with a radius of 71 Å. These results indicate that the complexes between the α 2-adrenoceptors and GTP binding regulatory proteins remain intact throughout the CHAPS solubilization procedure.