Summary.
Background: Several studies have indicated that quercetin promotes relaxation of vascular smooth muscle both in vivo and in vitro. However, Saponara et al. [(2002) Br J Pharmacol 135: 1819–1827] have demonstrated that quercetin is an activator of vascular L-type Ca2+ channels. Aim of the study :We investigated the mechanical and electrophysiological properties of quercetin and its rutoside, rutin, in an attempt to clarify how Ca2+ channel activation might be related to the myorelaxing activity. Methods: Aorta ring preparations and single tail artery myocytes were employed for functional and patch-clamp experiments, respectively. Results: Rutin was found to relax intact rat aorta rings, which had been precontracted with phenylephrine (pIC50 = 5.65 ± 0.31) but in contrast had no effect on depolarised (60 mM K+) preparations or on those from which the endothelium had been removed. Furthermore, rutin did not affect L-type Ca2+ current recorded in rat tail artery myocytes. The quercetin-induced relaxation of intact rings precontracted with phenylephrine exhibited two components characterised by 6.23 ± 0.38 and 4.66 ± 0.09 pIC50, respectively. Removal of the endothelium abolished the first component, leaving the second unaltered. Moreover, quercetin was found to relax 60 mM K+ depolarised rings with a pIC50 of 4.59 ± 0.03. The application of quercetin in isolated smooth muscle cells brought about a marked increase of L-type Ca2+ current (pEC50 = 5.09 ± 0.05). Unlike quercetin, Bay K 8644 contracted aorta rings preincubated with 10, 20 or 30 mM K+ . The myotonic effect of Bay K 8644 was observed both in the absence or presence of 30 μM quercetin. The application of Bay K 8644 (10–100 nM) caused a further significant increase in L-type Ca2+ current in rat tail artery myocytes stimulated with 30 μM quercetin. Conclusions: Quercetin is a naturally occurring L-type Ca2+ channel agonist. This effect, however, is overwhelmed by quercetin-induced vasorelaxation taking place via pathways which are more relevant than L-type Ca2+ influx in the hierarchy of functional competencies.
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Received: 15 July 2002, Accepted: 25 October 2002
Correspondence to: G. Sgaragli
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Fusi, F., Saponara, S., Pessina, F. et al. Effects of quercetin and rutin on vascular preparations . Eur J Nutr 42, 10–17 (2003). https://doi.org/10.1007/s00394-003-0395-5
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DOI: https://doi.org/10.1007/s00394-003-0395-5