Identification and characterization of novel properties of the human D3 dopamine receptor.

Among dopamine receptors, the function and properties of the D3 receptor subtype are poorly understood. Here we report the identification and characterization of two unique properties of the human D3 receptor. The D3 receptor exhibits a tolerance property wherein the magnitude of the second agonist-induced response is reduced by 60% compared to the first response and progressively decreases upon repeated agonist application. In addition, unlike the D2 dopamine receptor, the D3 receptor response terminates 15-fold more slowly upon agonist removal. Using D3/D2S chimeric receptors, we demonstrate that D3 receptor tolerance property is mediated by a novel conformational mechanism involving the D3 receptor second cytoplasmic region. The slow response termination rate property requires the third cytoplasmic region and is due to the high affinity of the D3 receptor for ligand as well as its unique G-protein signaling mechanism.