Alpha 1A/B-Knockout mice explain the native Alpha 1D-adrenoceptor's role in vasoconstriction and show that its location is independent of the other Alpha 1-subtypes

Methven, L., Simpson, P.C. and McGrath, J.C. (2009) Alpha 1A/B-Knockout mice explain the native Alpha 1D-adrenoceptor's role in vasoconstriction and show that its location is independent of the other Alpha 1-subtypes. British Journal of Pharmacology, 158(7), pp. 1663-1675. (doi: 10.1111/j.1476-5381.2009.00462.x)

Abstract

Background and purpose: Theoretically, three a1-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 a1A/B-adrenoceptor knockout mouse (a1A/B-KO) was used to study the isolated a1D-adrenoceptor to consider these potential interactions in native tissue.Experimental approach: Pharmacological analysis of carotid and mesenteric arteries employed wire myography and fluorescent ligand binding (a1-adrenoceptor ligand BODIPY FL-prazosin, QAPB).Key results: a1A/B-KO carotid had clear a1D-adrenoceptor-induced contractions. In WT carotid a1D-adrenoceptor dominated but all three a1-subtypes participated. a1A/B-KO mesenteric had a1D-adrenoceptor responses with high sensitivity and small maximum, explaining how a1D-adrenoceptor could determine agonist sensitivity in WT. In both arteries a1A/B-KO fluorescence levels were reduced but pharmacologically more consistent with 'pure'a1D-adrenoceptors. a1D-Adrenoceptor binding in a1A/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 and implications: 'Pure'a1D-adrenoceptor pharmacology in a1A/B-KO provides a quantitative standard. Functionally, the a1D- and a1A-adrenoceptors produce additive responses and do not significantly compensate for each other. a1D-Adrenoceptor contributes to sensitivity even in resistance arteries. In a1A/B-KO, the loss of a1A- and a1B-adrenoceptors is reflected by a general decrease in fluorescence, but similar binding distribution to WT indicates that the a1D-adrenoceptor location in native smooth-muscle cells is not influenced by other a1-adrenoceptors. Equivalent levels of receptors did not correspond to equivalent responses. In conclusion, a1-subtypes do not interact but provide independent alternative signals for vascular regulation.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: McGrath, Professor John and Methven, Dr Laura
• Authors: Methven, L., Simpson, P.C., and McGrath, J.C.
• College/School: College of Medical Veterinary and Life Sciences > School of Life Sciences
• Journal Name: British Journal of Pharmacology
• ISSN: 00071188