Dopamine D2 receptors internalize in their low-affinity state.

The present study was done in order to determine whether dopamine internalizes D2 receptors in CHO cells and whether the high-affinity or the low-affinity state of the dopamine D2 receptor is associated with dopamine-induced internalization of dopamine D2 receptors. Using [3H]sulpiride to label D2Long receptors in CHO cells, it was found that dopamine lowered the binding of [3H]sulpiride by 20%. Although the high-affinity states of D2 were converted to low-affinity states by guanine nucleotide, the latter had no effect in blocking the dopamine-induced reduction in [3H]sulpiride binding, indicating that the dopamine-induced internalization of D2 receptors occurred with D2 in the low-affinity state.