title: A novel fluorescent histamine H(1)  receptor antagonist demonstrates the advantage of using fluorescence correlation spectroscopy to study the binding of lipophilic ligands.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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).
  
  
  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
  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.
authors: Institute of Cell Signalling, School of Biomedical Sciences, University of Nottingham, Nottingham, UK.
authors: Rachel H
authors: RH
authors: Rose
authors: Institute of Cell Signalling, School of Biomedical Sciences, University of Nottingham, Nottingham, UK.
authors: Stephen J
authors: SJ
authors: Briddon
authors: Institute of Cell Signalling, School of Biomedical Sciences, University of Nottingham, Nottingham, UK.
authors: Stephen J
authors: SJ
authors: Hill
mesh_terms: D000818:Animals; D001896:Boron Compounds / Q000494:pharmacology*; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D006367:HeLa Cells; D006634:Histamine H1 Antagonists / Q000494:pharmacology*; D006801:Humans; D008024:Ligands; D011738:Pyrilamine / Q000031:analogs & derivatives* / Q000494:pharmacology; D011969:Receptors, Histamine H1 / Q000235:genetics / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
chemical_list: D001896:Boron Compounds; D006634:Histamine H1 Antagonists; D008024:Ligands; D011969:Receptors, Histamine H1; C573317:mepyramine-BODIPY630-650; D011738:Pyrilamine; D002118:Calcium