Characterization of a novel iodinated ligand, IPMPP, for human dopamine D4 receptors expressed in CHO cells

LIFE SCIENCES

卷:60

Article

Kung, MP ; Stevenson, DA ; Zhuang, ZP ; Vessotskie, JM ; Chumpradit, S ; Sun, XM ; Kung, HF

关键词: radioiodinated ligand;    G protein-coupling;    dopamine D4 receptors;    agonist;    antagonist;    high-affinity binding;   

DOI  :  10.1016/S0024-3205(96)00598-X

来源: Elsevier

【 摘 要 】

A novel radioiodinated ligand with a high specific activity (2,200 Ci/mmol), 3-[4-(4-iodophenyl)piperazin-1-yl]methyl-1H-pyrrolo(2,3-b) pyridine ([I-125]IPMPP), was successfully prepared. Binding characteristics of [I-125]IPMPP were evaluated using human dopamine D4 (D4.2 variant) receptors expressed in Chinese hamster ovary (CHO) cells. Saturation analysis revealed high affinity binding sites for [I-125]IPMPP (K-d = 0.39 +/- 0.18 nM). The number of D4 receptors labeled with [I-125]IPMPP at room temperature was four times higher than that labeled with [I-125]S(-)5-OH-PIPAT, a radioiodinated agonist ligand (572 fmol/mg protein vs. 125 fmol/mg protein). A significant decrease in the number of binding sites was observed with [I-125]S(-)5-OH-PIPAT when assays were carried out at a higher temperature (37 degrees C vs. 25 degrees C). In contrast to [I-125]S(-)5-OH-PIPAT, [I-125]IPMPP labeled more D4 sites at 37 degrees C. Neither magnesium ion nor guanylimidodiphosphate (Gpp(NH)p) affected [I-125]IPMPP binding. These data support the conclusion that [I-125]IPMPP is an antagonist ligand. The potency of various compounds, including clozapine, to inhibit [I-125]IPMPP binding is consistent with the rank order measured with other radioligands for D4 receptors. In addition, measuring D4 receptor stimulation of [S-35]GTP gamma S binding further demonstrated the antagonist property of IPMPP.

【 授权许可】

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