Temperature Sensitivity of Agonist High-Affinity Binding Sites of Solubilized and Reconstituted D1 Dopamine Receptors

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Abstract
Solubilization of rat striatal membranes with sodium cholate, followed by reconstitution into phospholipid vesicles, leads to a 6.5-fold increase in the agonist high-affinity binding sites of the D1 dopamine receptor. These high-affinity binding sites display differential sensitivity toward temperature. When reconstituted receptors were preincubated for 1 h at 0-4 degrees C (on ice) or at 22 degrees C (room temperature) followed by radioligand binding assays with dopamine, neither the high-affinity values of the receptor for dopamine nor the percent receptors in the high-affinity state (31-39%) were changed from control reconstituted receptors, which were not subject to any preincubations. At 30 degrees C, there was a partial loss in the number of high-affinity D1 receptors with only 25% of the total receptor population in the high-affinity state; there was no change in the affinity values of the high-affinity binding sites. At 37 degrees C, there was a 40% loss in total number of D1 receptor binding sites. All the high-affinity binding sites were lost and the remaining 60% of binding activity represented the low-affinity binding state of the receptor. These results indicate that the high-affinity binding sites of the reconstituted D1 dopamine receptors are uniquely sensitive to higher temperatures.

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