Fluorescent ligand binding reveals heterogeneous distribution of adrenoceptors and 'cannabinoid-like' receptors in small arteries

Abstract

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 -adrenoceptors, -adrenoceptors and cannabinoid-like (GPR55) receptors in the mouse arteries. Experimental approach: Fluorescence intensity from vascular tissue incubated with fluorescent ligands ( 1- adrenoceptor ligand, BODIPY-FL-prazosin, QAPB; -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 1B/D-adrenoceptor-KO mice were used. Key results: T1117, a fluorescent form of the cannabinoid CB 1 receptor antagonist AM251, was a ligand for GPR55, with low affinity for CB 1 receptors. In mesenteric arterial smooth muscle cells, 1A-adrenoceptors were predominantly located in different cells from those with -adrenoceptors, angiotensin receptors or cannabinoid-like (GPR55) receptors. Cells with -adrenoceptors predominated at arterial branches. Endothelial cells expressed -adrenoceptors, -adrenoceptors and cannabinoid-like receptors. Only endothelial -adrenoceptors appeared in clusters. Adventitia was a rich source of G protein-coupled receptors (GPCRs), particularly fibroblasts and nerve tracts, where Schwann cells bound -adrenoceptor, -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. © 2010 The British Pharmacological Society. All rights reserved.