Fluorescent ligand binding reveals heterogeneous distribution of adrenoceptors and ‘cannabinoid‐like’ receptors in small arteries

• Published in: British journal of pharmacology 2010-02, Vol.159 (4), p.787-796
• Main Authors: Daly, CJ, Ross, RA, Whyte, J, Henstridge, CM, Irving, AJ, McGrath, JC
• Format: Article
• Language: English
• Subjects: adrenoceptor; adventitia; angiotensin; Angiotensin II - metabolism; Animals; Biological and medical sciences; Boron Compounds - metabolism; cannabinoid; confocal microscopy; Connective Tissue - metabolism; endothelium; Endothelium, Vascular - metabolism; Fluorescent Dyes - metabolism; fluorescent ligand binding; Ligands; Localization; Male; Medical sciences; Mesenteric Arteries - cytology; Mesenteric Arteries - metabolism; Mice; Mice, Inbred C57BL; Mice, Knockout; Microscopy, Confocal; Molecular Imaging; Molecular Probe Techniques; Muscle, Smooth, Vascular - metabolism; Pharmacology. Drug treatments; Prazosin - analogs & derivatives; Prazosin - metabolism; Propanolamines - metabolism; Pyrazoles - metabolism; Rats; Rats, Wistar; Receptors, Adrenergic - deficiency; Receptors, Adrenergic - genetics; Receptors, Adrenergic - metabolism; Receptors, Adrenergic, alpha-1 - metabolism; Receptors, Adrenergic, beta - metabolism; Receptors, Cannabinoid - metabolism; Rodents; Tail - blood supply; Themed Section: Research Papers; vascular smooth muscle; Veins & arteries; α1B/D‐adrenoceptor knockout
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1111/j.1476-5381.2009.00608.x

Background and purpose:  Pharmacological analysis of synergism or functional antagonism between different receptors commonly assumes that interacting receptors are located in the same cells. We have now investigated the distribution of α‐adrenoceptors, β‐adrenoceptors and cannabinoid‐like (GPR55) receptors in the mouse arteries. Experimental approach:  Fluorescence intensity from vascular tissue incubated with fluorescent ligands (α1‐adrenoceptor ligand, BODIPY‐FL‐prazosin, QAPB; β‐adrenoceptor ligand, TMR‐CGP12177; fluorescent angiotensin II; a novel diarylpyrazole cannabinoid ligand (Tocrifluor 1117, T1117) was measured with confocal microscopy. Small mesenteric and tail arteries of wild‐type and α1B/D‐adrenoceptor‐KO mice were used. Key results:  T1117, a fluorescent form of the cannabinoid CB1 receptor antagonist AM251, was a ligand for GPR55, with low affinity for CB1 receptors. In mesenteric arterial smooth muscle cells, α1A‐adrenoceptors were predominantly located in different cells from those with β‐adrenoceptors, angiotensin receptors or cannabinoid‐like (GPR55) receptors. Cells with β‐adrenoceptors predominated at arterial branches. Endothelial cells expressed β‐adrenoceptors, α‐adrenoceptors and cannabinoid‐like receptors. Only endothelial α‐adrenoceptors appeared in clusters. Adventitia was a rich source of G protein‐coupled receptors (GPCRs), particularly fibroblasts and nerve tracts, where Schwann cells bound α‐adrenoceptor, β‐adrenoceptor and CB‐receptor ligands, with a mix of separate receptor locations and co‐localization. Conclusions and implications:  Within each cell type, each GPCR had a distinctive heterogeneous distribution with limited co‐localization, providing a guide to the possibilities for functional synergism, and suggesting a new paradigm for synergism in which interactions may be either between cells or involve converging intracellular signalling processes. This article is part of a themed section on Imaging in Pharmacology. To view the editorial for this themed section visit http://dx.doi.org/10.1111/j.1476‐5381.2010.00685.x