Abstract 1182: Lack of Caveolae in Caveolin-1 Knock-out Mice Modulates Adrenoceptor-mediated Function in Small Arteries
Background: The scaffolding protein caveolin maintains structural integrity of small cell membrane invaginations (caveolae) and modulates function of co-localised proteins including α- and β-adrenoceptors (β-ARs). In caveolin-1 knock-out mice (cav-1KO) we studied the functional consequences of lack of caveolae on vascular contractile responses to α- and β-AR stimulation of saphenous artery.
Methods: Rings of saphenous artery (1–2 mm long) from wild type CD57Black6 (WT) and cav-1KO mice (9–18 months) were mounted in a Halpern-Mulvany myograph and isometric force of contraction was measured at 70 mmHg wall tension. Total RNA was measured with real-time PCR analysis.
Results: Electron microscopy revealed absence of caveolae from arterial muscle cells of cav-1KO. The mRNA levels for α1A-, α1B-, α1D-, β1-, β2- and β3-ARs were similar in arteries from both groups. Cav-1KO arteries were hypertrophic and contracted more strongly in response to the α-AR agonist (-)noradrenaline, i.e. 4.2±0.2 vs. in cav-1KO and 2.9±0.2 mN/mm in WT, although potencies were similar (-logEC50M 7.1±0.1 and 7.3±0.2). The α1-AR antagonist prazosin (1 μM) reduced basal tension of arteries from cav-1KO but not from WT mice, suggesting neuronal leak of noradrenaline in cav-1KO. (-)Isoprenaline relaxed KCl-contracted arteries from cav-1KO less potently than WT (-logEC50M 6.8 and 7.3). These responses were partially and similarly antagonised by the β2-AR antagonist ICI118551 (50nM) in both groups, whereas the partial antagonism by the β1-AR antagonist CGP20712A (300nM) was present only in WT but not in cav-1KO arteries. Conversely, the β3-AR antagonist L748337 (100nM) partially antagonised the relaxation in cav-1KO only. Consistently, the selective β3-AR agonist BRL37344 partially relaxed arteries through β3-AR in cav-1KO.
Conclusion: Despite of neuronal leak in cav-1KO, noradrenaline potency at arterial α1- and β2-ARs is similar. In contrast, the loss of β1-AR function unmasks β3-AR-mediated relaxation. Since loss of caveolae did not affect mRNA expression of vascular AR subtypes, we speculate that the functional changes in cav-1 KO reflect caveolar and extra-caveolar location of β1- and β3-ARs, respectively.