Properties of rat striatal D-2 dopamine receptors solubilized with the zwitterionic detergent CHAPS

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Abstract
The specific binding of [3 H]spiperone was determined in membrane preparations of rat striatum and following solubilization treatment with the zwitterionic detergent CHAPS. Membrane protein solubilization was confirmed by ultrafiltration, gel filtration and increased heat sensitivity. Specific binding of [3 H]spiperone to the solubilized preparation was saturable and of high affinity, although solubilization led to an approximate 10 fold decrease in receptor affinity for [3 H]spiperone. The drug displacement profile of binding to the CHAPS solubilized preparation corresponded to that of the dopamine D-2 receptor; binding was stereoselectively displaced by the isomers of butaclamol. The sodium dependence of sulpiride displacement of specific [3 H]spiperone binding was retained in the CHAPS solubilized preparation. GTP (100 μM) only altered the ability of dopamine to displace [3 H]spiperone binding to the solubilized preparation in the presence of 120 mM sodium chloride. The GTP effect was small compared with that observed in the membranes. Specific [3 H]spiperone binding sites in the solubilized preparation were preferentially retained by a wheat germ agglutinin affinity column and subsequently eluted with N-acetyl-D-glucosamine. Gel filtration of the solubilized preparation using a Sepharose column resulted in two peaks of specific [3 H]spiperone binding, the larger component had a Stokes radius of 7.7 nm. CHAPS treatment of rat striatal membranes results in solubilization of the D-2 receptor in an active form. The D-2 site appears to be a glycoprotein of high molecular weight.