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. 2009 Dec 2;35(3):806–817. doi: 10.1038/npp.2009.189

Figure 4.

Figure 4

Competition binding of [3H]raclopride or [3H]NMSP under control and internalization conditions. (a) [3H]Raclopride binding in competition with sulpiride. A two-site binding curve was observed in control cells (○, Q−). Most D2 receptors (85.8%) were on the surface and showed high affinity (Ki(s)=7.7±2.3 nM). A small proportion (14.2%) were internalized and showed low-affinity binding (Ki(i)=141.8±45.2 μM). Following quinpirole treatment (•, Q+), 43.1% of D2 receptors remained on the surface (Ki(s)=7.9±3.0 nM) and 56.9% were internalized (Ki(i)=120.7±35.8 μM). (b) [3H]NMSP binding in competition with raclopride. Competition experiments showed indistinguishable one-site binding curves between control (○, Q− Ki=0.26±0.09 nM) and quinpirole-treated cells (•, Q+ Ki=0.28±0.05 nM). Thus, similar to NMSP, raclopride readily accesses internalized D2 receptors.