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Background: ATP-sensitive inward rectifier potassium channels (Kir), are a potassium channel family involved in many physiological processes. KATP dysfunctions are observed in several diseases such as hypoglycaemia, hyperinsulinemia, Prinzmetal angina–like symptoms, cardiovascular diseases. Methods: A broader view of the KATP mechanism is needed in order to operate on their regulation, and in this work we clarify the structure of the Rattus norvegicus ATP-sensitive inward rectifier potassium channel 8 (Kir6.1), which has been obtained through a homology modelling procedure. Due to the medical use of flavonoids, a considerable increase in studies on their influence on human health has recently been observed, therefore our aim is to study, through computational methods, the three-dimensional (3D) conformation together with mechanism of action of Kir6.1 with three flavonoids. Results: Computational analysis by performing molecular dynamics (MD) and docking simulation on rat 3D modelled structure have been completed, in its closed and open conformation state and in complex with Quercetin, 5-Hydroxyflavone and Rutin flavonoids. Our study showed that only Quercetin and 5-Hydroxyflavone were responsible for a significant down-regulation of the Kir6.1 activity, stabilising it in a closed conformation. This hypothesis was supported by in vitro experiments demonstrating that Quercetin and 5-Hydroxyflavone were capable to inhibit KATP currents of rat tail main artery myocytes recorded by the patch-clamp technique. Conclusion: Combined methodological approaches, such as molecular modelling, docking and MD simulations of Kir6.1 channel, used to elucidate flavonoids intrinsic mechanism of action, are introduced, revealing a new potential druggable protein site. [ABSTRACT FROM AUTHOR]

Ion channels underlie a wide variety of physiological processes that involve rapid changes in cell dynamics, such as cardiac and vascular smooth muscle contraction. Overexpression or dysfunction of these membrane proteins are the basis of many cardiovascular diseases that represent the leading cause of morbidity and mortality for human beings. In the last few years, flavonoids, widely distributed in the plant kingdom, have attracted the interest of many laboratories as an emerging class of fine ion, in particular Ca v , channels modulators. Pieces of in vitro evidence for direct as well as indirect effects exerted by various flavonoids on ion channel currents are now accumulating in the scientific literature. This activity may be responsible, at least in part, for the beneficial and protective effects of dietary flavonoids toward cardiovascular diseases highlighted in several epidemiological studies. Here we examine numerous studies aimed at analysing this feature of flavonoids, focusing on the mechanisms that promote their sometimes controversial activities at cardiovascular Ca v channels. New methodological approaches, such as molecular modelling and docking to Ca v 1.2 channel α 1c subunit, used to elucidate flavonoids intrinsic mechanism of action, are introduced. Moreover, flavonoid-membrane interaction, bioavailability, and antioxidant activity are taken into account and discussed. [ABSTRACT FROM AUTHOR]

Quercetin and ferulic acid are two phytochemicals extensively represented in the plant kingdom and daily consumed in considerable amounts through diets. Due to a common phenolic structure, these two molecules share several pharmacological properties, e.g., antioxidant and free radical scavenging, anti-cancer, anti-inflammatory, anti-arrhythmic, and vasorelaxant. The aim of the present work was the combination of the two molecules in a single chemical entity, conceivably endowed with more efficacious vasorelaxant activity. Preliminary in silico studies herein described suggested that the new hybrid compound bound spontaneously and with high affinity on the KCa1.1 channel. Thus, the synthesis of the 3′-ferulic ester derivative of quercetin was achieved and its structure confirmed by 1H- and 13C-NMR spectra, HSQC and HMBC experiments, mass spectrometry, and elementary analysis. The effect of the new hybrid compound on vascular KCa1.1 and CaV1.2 channels revealed a partial loss of the stimulatory activity that characterizes the parent compound quercetin. Therefore, further studies are necessary to identify a better strategy to improve the vascular properties of this flavonoid. [ABSTRACT FROM AUTHOR]

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 Ca[sup 2+] channels. Aim of the study :We investigated the mechanical and electrophysiological properties of quercetin and its rutoside, rutin, in an attempt to clarify how Ca[sup 2+] 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 (pIC[sub 50] = 5.65 ± 0.31) but in contrast had no effect on depolarised (60 mM K[sup +] ) preparations or on those from which the endothelium had been removed. Furthermore, rutin did not affect L-type Ca[sup 2+] 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 pIC[sub 50] , respectively. Removal of the endothelium abolished the first component, leaving the second unaltered. Moreover, quercetin was found to relax 60 mM K[sup +] depolarised rings with a pIC[sub 50] of 4.59 ± 0.03. The application of quercetin in isolated smooth muscle cells brought about a marked increase of L-type Ca[sup 2+] current (pEC[sub 50] = 5.09 ± 0.05). Unlike quercetin, Bay K 8644 contracted aorta rings preincubated with 10, 20 or 30 mM K[sup +] . 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 Ca[sup 2+] current in rat tail artery myocytes stimulated with 30 μM quercetin. Conclusions: Quercetin is a... [ABSTRACT FROM AUTHOR]

1 The aim of this study was to investigate the effects of quereetin, a natural polyphenolic flavonoid, on voltage-dependent Ca[sup2+] channels of smooth muscle cells freshly isolated from the rat tail artery, using either the conventional or the amphotericin B-perforated whole-cell patch-clamp method. 2 Quercetin increased L-type Ca[sup2] current[I[sub Ca(L)] in a concentration- (pEC[sub50]= 5.09±0.05) and voltage-dependent manner and shifted the maximum of the current-voltage relationship by 10 mV in the hyperpolarizing direction, without, however, modifying the threshold and the equilibrium potential for Ca[sup2+], Quercetin-indueed I[subCa(L)] stimulation was reversible upon wash-out. T-type Ca[sup2] current was not affected by quercetin. 3 Quercetin shifted the voltage dependence of the steady-state inactivation and activation curves to more negative potentials by about 5.5 and 7.5 mV respectively, in the mid-potential of the curves as well as increasing the slope of activation. Quercetin slowed both the activation and the deactivation kinetics of the I[subCa(L)]. The inactivation time course was also slowed but only at voltages higher than 10 mV. Moreover quercetin slowed the rate of recovery from inactivation. 4 These results prove quercetin to be a naturally-occurring L-type Ca[sup2] channel activator. [ABSTRACT FROM AUTHOR]

[Display omitted] Flavonoids, ubiquitously distributed in the plant world, are regularly ingested with diets rich in fruit, vegetables, wine, and tea. During digestion, they are partially absorbed in the stomach. The present work aimed to assess the in vitro effects of quercetin and ten structurally related flavonoids on the rat gastric fundus smooth muscle, focussing on ATP-dependent K+ (K ir 6.1) channels, which play a central role in the regulation of resting membrane potential, membrane excitability and, consequently, of gastric motility. Whole-cell currents through K ir 6.1 channels (I Kir6.1) were recorded with the patch-clamp technique and the mechanical activity of gastric fundus smooth muscle strips was studied under isometric conditions. Galangin ≈ tamarixetin > quercetin > kaempferol > isorhamnetin ≈ luteolin ≈ fisetin > (±)-taxifolin inhibited pinacidil-evoked, glibenclamide-sensitive I Kir6.1 in a concentration-dependent manner. Morin, rutin, and myricetin were ineffective. The steric hindrance of the molecule and the number and position of hydroxyl groups on the B ring played an important role in the activity of the molecule. Molecular docking simulations revealed a possible binding site for flavonoids in the C-terminal domain of the K ir 6.1 channel subunit SUR2B, in a flexible loop formed by residues 251 to 254 of chains C and D. Galangin and tamarixetin, but not rutin relaxed both high K+- and carbachol-induced contraction of fundus strips in a concentration-dependent manner. Furthermore, both flavonoids shifted to the right the concentration-relaxation curves to either pinacidil or L-cysteine constructed in strips pre-contracted by high K+, rutin being ineffective. In conclusion, I Kir6.1 inhibition exerted by dietary flavonoids might counterbalance their myorelaxant activity, affect gastric accommodation or, at least, some stages of digestion. [ABSTRACT FROM AUTHOR]

Abstract: The functional interaction between two L-type Ca2+ channel activators, quercetin and (S)-(−)-methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)pyridine-5-carboxylate (Bay K 8644), has been investigated in vascular smooth muscle cells. L-type Ca2+ currents [I Ca(L)] were recorded in freshly isolated rat tail main artery myocytes using the whole-cell patch-clamp method. Bay K 8644 increased I Ca(L) in a concentration-dependent manner with a pEC50 value of 8.25. Pre-incubation of myocytes with concentrations of quercetin per se ineffective as an L-type Ca2+ channel activator (0.1 and 0.3 μM) inhibited significantly the maximal response evoked by Bay K 8644, but left unaltered its potency. Quercetin (0.1 μM) prevented the hyperpolarizing shift of the steady-state inactivation curve induced by 0.1 μM Bay K 8644 and its stimulation of I Ca(L) tail current intensity without modifying Bay K 8644-induced effects on I Ca(L) activation, inactivation, deactivation kinetics as well as on use-dependence and recovery from inactivation. Quercetin at nutritionally meaningful concentrations, limited the responsiveness of vascular L-type Ca2+ channels to the pharmacological stimulation operated by Bay K 8644. These data contribute to a better understanding of quercetin effects on experimental in vivo cardioprotection. [Copyright &y& Elsevier]

Quercetin, a flavonoid abundantly present in the Mediterranean diet, is considered a vasodilator despite its recognized capability to stimulate vascular Ca V 1.2 channel current (I Ca1.2). The present study was undertaken to assess its possible vasocontractile activity. Functional and electrophysiology experiments were performed in vitro on rat aorta rings and tail artery myocytes along with an in-depth molecular modelling analysis. The Ca V 1.2 channel stimulator (S)-(−)-methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl) pyridine-5-carboxylate (Bay K 8644) was used as reference compound. Quercetin and Bay K 8644 caused a significant leftward shift of KCl concentration-response curve. Neither agent affected basal muscle tone, though in rings pre-treated with thapsigargin or 15 mM KCl they caused a strong, concentration-dependent contraction. Both quercetin and Bay K 8644 potentiated the response to Ca2+ in weakly depolarised rings. At high KCl concentrations, however, quercetin caused vasorelaxation. While Bay K 8644 stimulated I Ca1.2 , this effect being sustained with time, quercetin-induced stimulation was transient, although the molecule in solution underwent only marginal oxidation. Quercetin transient stimulation was not affected by pre-treatment with isoprenaline, sodium nitroprusside, or dephostatin; however, it converted to a sustained one in myocytes pre-incubated with Gö6976. Classical molecular dynamics simulations revealed that quercetin and Bay K 8644 formed hydrogen bonds with target sensing residues of Ca V 1.2 channel favouring the inactivated conformation. In conclusion, quercetin-induced stimulation of I Ca1.2 promoted vasocontraction when Ca2+ buffering function of sarcoplasmic reticulum was impaired and/or smooth muscle cell membrane was moderately depolarised, as it may occur under certain pathological conditions. [ABSTRACT FROM AUTHOR]

• Twenty-four quercetin derivatives were designed according to the key chemically reactive centers. • A rational docking simulation was carried out to obtain the most accurate binding mode for each ligand. • Semi-synthetic hybrids were synthesized endowing substituents with known vasoactive properties. • Three hybrids bind inside the K Ca 1.1 channel binding pocket located in the S6/RCK linker. • The derivatization of quercetin in C7 and C4′ position improves its beneficial vascular activity. Quercetin represents one of the most studied dietary flavonoids; it exerts a panel of pharmacological activities particularly on the cardiovascular system. Stimulation of vascular K Ca 1.1 channels contributes to its vasorelaxant activity, which is, however, counteracted in part by its concomitant stimulation of Ca V 1.2 channels. Therefore, several quercetin hybrid derivatives were designed and synthesized to produce a more selective K Ca 1.1 channel stimulator, then assessed both in silico and in vitro. All the derivatives interacted with the K Ca 1.1 channel with similar binding energy values. Among the selected derivatives, 1E was a weak vasodilator, though displaying an interesting Ca V 1.2 channel blocking activity. The lipoyl derivatives 1F and 3F , though showing pharmacological and electrophysiological features similar to those of quercetin, seemed to be more effective as K Ca 1.1 channel stimulators as compared to the parent compound. The strategy pursued demonstrated how different chemical substituents on the quercetin core can change/invert its effect on Ca V 1.2 channels or enhance its K Ca 1.1 channel stimulatory activity, thus opening new avenues for the synthesis of efficacious vasorelaxant quercetin hybrids. [ABSTRACT FROM AUTHOR]