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A novel fluorescent histamine H 1 receptor antagonist demonstrates the advantage of using fluorescence correlation spectroscopy to study the binding of lipophilic ligands
Author(s) -
Rose Rachel H,
Briddon Stephen J,
Hill Stephen J
Publication year - 2012
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.2011.01640.x
Subject(s) - mepyramine , confocal microscopy , receptor , biophysics , yellow fluorescent protein , histamine , chemistry , histamine receptor , ligand (biochemistry) , histamine h1 receptor , fluorescence , antagonist , fluorescence microscope , receptor antagonist , biology , biochemistry , microbiology and biotechnology , pharmacology , physics , quantum mechanics , gene
BACKGROUND AND PURPOSE Fluorescent ligands facilitate the study of ligand–receptor interactions at the level of single cells and individual receptors. Here, we describe a novel fluorescent histamine H 1 receptor antagonist (mepyramine‐BODIPY630‐650) and use it to monitor the membrane diffusion of the histamine H 1 receptor. EXPERIMENTAL APPROACH The human histamine H 1 receptor fused to yellow fluorescent protein (YFP) was transiently expressed in CHO‐K1 cells. The time course of binding of mepyramine‐BODIPY630‐650 to the H 1 receptor was determined by confocal microscopy. Additionally, fluorescence correlation spectroscopy (FCS) was used to characterize the diffusion coefficient of the H 1 receptor in cell membranes both directly (YFP fluorescence) and in its antagonist‐bound state (with mepyramine‐BODIPY630‐650). KEY RESULTS Mepyramine‐BODIPY630‐650 was a high‐affinity antagonist at the histamine H 1 receptor. Specific membrane binding, in addition to significant intracellular uptake of the fluorescent ligand, was detected by confocal microscopy. However, FCS was able to quantify the receptor‐specific binding in the membrane, as well as the diffusion coefficient of the antagonist–H 1 receptor–YFP complexes, which was significantly slower than when determined directly using YFP. FCS also detected specific binding of mepyramine‐BODIPY630‐650 to the endogenous H 1 receptor in HeLa cells. CONCLUSIONS AND IMPLICATIONS Mepyramine‐BODIPY630‐650 is a useful tool for localizing the H 1 receptor using confocal microscopy. However, its use in conjunction with FCS allows quantification of ligand binding at the membrane, as well as determining receptor diffusion in the absence of significant bleaching effects. Finally, these methods can be successfully extended to endogenously expressed untagged receptors in HeLa cells.