The alpha 1B/D-adrenoceptor knockout mouse permits isolation of the vascular alpha 1A-adrenoceptor and elucidates its relationship to the other subtypes.
OBJECTIVE
Mesenteric and carotid arteries from the alpha(1B/D)-adrenoceptor knockout (alpha(1B/D)-KO) were employed to isolate alpha(1A)-adrenoceptor pharmacology and location and to reveal these features in the wild-type (WT) mouse.


METHODS
Functional pharmacology by wire myography and receptor localization by confocal microscopy, using the fluorescent alpha(1)-adrenoceptor ligand BODIPY FL-Prazosin (QAPB), on mesenteric (an 'alpha(1A)-adrenoceptor' tissue) and carotid (an 'alpha(1D)-adrenoceptor' tissue) arteries.


RESULTS
Alpha(1B/D)-KO mesenteric arteries showed straightforward alpha(1A)-adrenoceptor agonist/antagonist pharmacology. WT had complex pharmacology with alpha(1A)- and alpha(1D)-adrenoceptor components. alpha(1B/D)-KO had a larger alpha(1A)-adrenoceptor response suggesting compensatory up-regulation: no increase in fluorescent ligand binding suggests up-regulation of signalling. alpha(1B/D)-KO carotid arteries had low efficacy alpha(1A)-adrenoceptor responses. WT had complex pharmacology consistent with co-activation of all three subtypes. Fluorescent binding had straightforward alpha(1A)-adrenoceptor characteristics in both arteries of alpha(1B/D)-KO. Fluorescent binding varied between cells in relative intracellular and surface distribution. Total fluorescence was reduced in the alpha(1B/D)-KO due to fewer smooth muscle cells showing fluorescent binding. WT binding was greater and sensitive to alpha(1A)- and alpha(1D)-adrenoceptor antagonists.


CONCLUSIONS
The straightforward pharmacology and fluorescent binding in the alpha(1B/D)-KO was used to interpret the properties of the alpha(1A)-adrenoceptor in the WT. Reduced total fluorescence in alpha(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 alpha(1B/D)-KO suggesting different cellular phenotypes of alpha(1A)-adrenoceptor exist. The alpha(1B/D)-KO provides robust assays for the alpha(1A)-adrenoceptor and takes us closer to understanding multi-receptor subtype interactions.
Methven
L
L
Integrative and Systems Biology, Faculty of Biomedical and Life Sciences, University of Glasgow, Glasgow, UK. l.methven@bio.gla.ac.uk
McBride
M
M
Wallace
G A
GA
McGrath
J C
JC
D000322:Adrenergic Agonists / Q000494:pharmacology; D018674:Adrenergic Antagonists / Q000494:pharmacology; D058646:Adrenergic alpha-1 Receptor Agonists; D000818:Animals; D002339:Carotid Arteries / Q000187:drug effects / Q000502:physiology; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D021122:Protein Subunits / Q000145:classification / Q000502:physiology*; D018340:Receptors, Adrenergic, alpha-1 / Q000145:classification / Q000172:deficiency / Q000502:physiology*
C547714:Adra1a protein, mouse; C547717:Adra1b protein, mouse; C547720:Adra1d protein, mouse; D000322:Adrenergic Agonists; D018674:Adrenergic Antagonists; D058646:Adrenergic alpha-1 Receptor Agonists; D021122:Protein Subunits; D018340:Receptors, Adrenergic, alpha-1