Alpha1A/B-knockout mice explain the native alpha1D-adrenoceptor's role in vasoconstriction and show that its location is independent of the other alpha1-subtypes.
OBJECTIVE
Theoretically, three alpha(1)-adrenoceptor subtypes can interact at the signalling level to alter vascular contraction or at the molecular level to alter each other's cellular location. The alpha(1A/B)-adrenoceptor knockout mouse (alpha(1A/B)-KO) was used to study the isolated alpha(1D)-adrenoceptor to consider these potential interactions in native tissue.


METHODS
Pharmacological analysis of carotid and mesenteric arteries employed wire myography and fluorescent ligand binding (alpha(1)-adrenoceptor ligand BODIPY FL-prazosin, QAPB).


RESULTS
alpha(1A/B)-KO carotid had clear alpha(1D)-adrenoceptor-induced contractions. In WT carotid alpha(1D)-adrenoceptor dominated but all three alpha(1)-subtypes participated. alpha(1A/B)-KO mesenteric had alpha(1D)-adrenoceptor responses with high sensitivity and small maximum, explaining how alpha(1D)-adrenoceptor could determine agonist sensitivity in WT. In both arteries alpha(1A/B)-KO fluorescence levels were reduced but pharmacologically more consistent with 'pure'alpha(1D)-adrenoceptors. alpha(1D)-Adrenoceptor binding in alpha(1A/B)-KO was observed on the cell surface and intracellularly and was present in a high proportion of smooth-muscle cells in both strains, regardless of artery type.


CONCLUSIONS
'Pure'alpha(1D)-adrenoceptor pharmacology in alpha(1A/B)-KO provides a quantitative standard. Functionally, the alpha(1D)- and alpha(1A)-adrenoceptors produce additive responses and do not significantly compensate for each other. alpha(1D)-Adrenoceptor contributes to sensitivity even in resistance arteries. In alpha(1A/B)-KO, the loss of alpha(1A)- and alpha(1B)-adrenoceptors is reflected by a general decrease in fluorescence, but similar binding distribution to WT indicates that the alpha(1D)-adrenoceptor location in native smooth-muscle cells is not influenced by other alpha(1)-adrenoceptors. Equivalent levels of receptors did not correspond to equivalent responses. In conclusion, alpha(1)-subtypes do not interact but provide independent alternative signals for vascular regulation.
Methven
L
L
Integrative and Systems Biology, Faculty of Biomedical and Life Sciences, University of Glasgow, Glasgow, UK. l.methven@bio.gla.ac.uk
Simpson
P C
PC
McGrath
J C
JC
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D002339:Carotid Arteries / Q000378:metabolism; D005453:Fluorescence; D008024:Ligands; D008297:Male; D008638:Mesenteric Arteries / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D032389:Myocytes, Smooth Muscle / Q000378:metabolism; D009213:Myography / Q000379:methods; D011485:Protein Binding; D018340:Receptors, Adrenergic, alpha-1 / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D014661:Vasoconstriction / Q000187:drug effects*
C547714:Adra1a protein, mouse; C547717:Adra1b protein, mouse; C547720:Adra1d protein, mouse; D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D008024:Ligands; D018340:Receptors, Adrenergic, alpha-1