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The α 1B/D ‐adrenoceptor knockout mouse permits isolation of the vascular α 1A ‐adrenoceptor and elucidates its relationship to the other subtypes
Author(s) -
Methven L,
McBride M,
Wallace GA,
McGrath JC
Publication year - 2009
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.1476-5381.2009.00269.x
Subject(s) - prazosin , mesenteric arteries , receptor , ligand (biochemistry) , adrenergic receptor , medicine , agonist , vascular smooth muscle , endocrinology , biology , chemistry , biophysics , antagonist , smooth muscle , artery
Background and purpose: Mesenteric and carotid arteries from the α 1B/D ‐adrenoceptor knockout (α 1B/D ‐KO) were employed to isolate α 1A ‐adrenoceptor pharmacology and location and to reveal these features in the wild‐type (WT) mouse. Experimental approach: Functional pharmacology by wire myography and receptor localization by confocal microscopy, using the fluorescent α 1 ‐adrenoceptor ligand BODIPY FL‐Prazosin (QAPB), on mesenteric (an ‘α 1A ‐adrenoceptor’ tissue) and carotid (an ‘α 1D ‐adrenoceptor’ tissue) arteries. Key results: α 1B/D ‐KO mesenteric arteries showed straightforward α 1A ‐adrenoceptor agonist/antagonist pharmacology. WT had complex pharmacology with α 1A ‐ and α 1D ‐adrenoceptor components. α 1B/D ‐KO had a larger α 1A ‐adrenoceptor response suggesting compensatory up‐regulation: no increase in fluorescent ligand binding suggests up‐regulation of signalling. α 1B/D ‐KO carotid arteries had low efficacy α 1A ‐adrenoceptor responses. WT had complex pharmacology consistent with co‐activation of all three subtypes. Fluorescent binding had straightforward α 1A ‐adrenoceptor characteristics in both arteries of α 1B/D ‐KO. Fluorescent binding varied between cells in relative intracellular and surface distribution. Total fluorescence was reduced in the α 1B/D ‐KO due to fewer smooth muscle cells showing fluorescent binding. WT binding was greater and sensitive to α 1A ‐ and α 1D ‐adrenoceptor antagonists. Conclusions and implications: The straightforward pharmacology and fluorescent binding in the α 1B/D ‐KO was used to interpret the properties of the α 1A ‐adrenoceptor in the WT. Reduced total fluorescence in α 1B/D ‐KO arteries, despite a clear difference in the functionally dominant subtype, indicates that measurement of receptor protein is unlikely to correlate with function. Fewer cells bound QAPB in the α 1B/D ‐KO suggesting different cellular phenotypes of α 1A ‐adrenoceptor exist. The α 1B/D ‐KO provides robust assays for the α 1A ‐adrenoceptor and takes us closer to understanding multi‐receptor subtype interactions.