Characterization of [125I]AR-M100613, a high-affinity radioligand for delta opioid receptors |
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Authors: | Fraser G L Labarre M Godbout C Butterworth J Clarke P B Payza K Schmidt R |
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Institution: | AstraZeneca R & D Montreal, St-Laurent, Quebec, Canada. |
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Abstract: | AR-M100613 (I]-Dmt-c-D-Orn-2-Nal-D-Pro-D-Ala-]) is the iodinated analog of a cyclic casomorphin previously shown to be a potent antagonist at the delta opioid receptor. Specific 125I]AR-M100613 binding to rat whole brain membranes was saturable, reversible, and best fit to a one-site model (Kd = 0.080 +/- 0.008 nM, Bmax = 45.2 +/- 4.4 fmol/mg protein). 125I]AR-M100613 binding was displaced with high affinity by the delta opioid receptor ligands SNC-80, Deltorphin II and DPDPE but not the mu or kappa-selective receptor ligands DAMGO and U69593. Residual non-selective binding of 125I]AR-M 100613 to mu opioid receptors is blocked by the addition of CTOP to the assay buffer. 35S]GTPgammaS binding assays indicate that AR-M100613 is a potent, selective, and reversible antagonist for delta opioid receptors in rat brain membranes. The high-affinity, high specific activity, low nonspecific binding and antagonist profile of 125I]AR-M100613 favor its use as a radiochemical probe for delta opioid receptors. |
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