L-type Ca(2+) channel current characteristics are preserved in rat tail artery myocytes after one-day storage

Vasorelaxant Activity of (2S)-Sakuranetin and Other Flavonoids Isolated from the Green Propolis of the Caatinga Mimosa tenuiflora

Some in vitro and in vivo evidence is consistent with the cardiovascular beneficial activity of propolis. As the single actors responsible for this effect have never been identified, an in-depth investigation of flavonoids isolated from the green propolis of the Caatinga Mimosa tenuiflora was performed and their mechanism of action was described. A comprehensive electrophysiology, functional, and molecular docking approach was applied. Most flavanones and flavones were effective CaV1.2 channel blockers with a potency order of (2S)-sakuranetin > eriodictyol-7,3'-methyl ether > quercetin 3-methyl ether > 5,4'-dihydroxy-6,7-dimethoxyflavanone > santin > axillarin > penduletin > kumatakenin, ermanin and viscosine being weak or modest stimulators. Except for eriodictyol 5-O-methyl ether, all the flavonoids were also effective spasmolytic agents of vascular rings, kumatakenin and viscosine also showing an endothelium-dependent activity. (2S)-Sakuranetin also stimulated KCa1.1 channels both in single myocytes and vascular rings. In silico analysis provided interesting insights into the mode of action of (2S)-sakuranetin within both CaV1.2 and KCa1.1 channels. The green propolis of the Caatinga Mimosa tenuiflora is a valuable source of multi-target vasoactive flavonoids: this evidence reinforces its nutraceutical value in the cardiovascular disease prevention arena.

3,3'-O-dimethylquercetin: A bi-functional vasodilator isolated from green propolis of the Caatinga Mimosa tenuiflora

In the search for novel, bi-functional compounds acting as CaV1.2 channel blockers and K+ channel stimulators, which represent an effective therapy for hypertension, 3,3'-O-dimethylquercetin was isolated for the first time from Brazilian Caatinga green propolis. Its effects were investigated through electrophysiological, functional, and computational approaches. In rat tail artery myocytes, 3,3'-O-dimethylquercetin blocked Ba2+ currents through CaV1.2 channels (IBa1.2) in a concentration-dependent manner, with the inhibition being reversed upon washout. The compound also shifted the voltage dependence of the steady-state inactivation curve to more negative potentials without affecting the slope of the inactivation and activation curves. Furthermore, the flavonoid stimulated KCa1.1 channel currents (IKCa1.1). In silico simulations provided additional evidence for the binding of 3,3'-O-dimethylquercetin to KCa1.1 and CaV1.2 channels and elucidated its mechanism of action. In depolarized rat tail artery rings, the flavonoid induced a concentration-dependent relaxation. Moreover, in rat aorta rings its antispasmodic effect was inversely related to the transmembrane K+ gradient. In conclusion, 3,3'-O-dimethylquercetin demonstrates effective in vitro vasodilatory properties, encouraging the exploration of its scaffold to develop novel derivatives for potential use in the treatment of hypertension.

Dynamin-independent CaV1.2 and KCa1.1 channels regulation and vascular tone modulation by the mitochondrial fission inhibitors dynasore and dyngo-4a

A role for mitochondrial fission in vascular contraction has been proposed based on the vasorelaxant activity of the dynamin (and mitochondrial fission) inhibitors mdivi-1 and dynasore. However, mdivi-1 is capable to inhibit Ba2+ currents through CaV1.2 channels (IBa1.2), stimulate KCa1.1 channel currents (IKCa1.1), and modulate pathways key to the maintenance of vessel active tone in a dynamin-independent manner. Using a multidisciplinary approach, the present study demonstrates that dynasore, like mdivi-1, is a bi-functional vasodilator, blocking IBa1.2 and stimulating IKCa1.1 in rat tail artery myocytes, as well as promoting relaxation of rat aorta rings pre-contracted by either high K+ or phenylephrine. Conversely, its analogue dyngo-4a, though inhibiting mitochondrial fission triggered by phenylephrine and stimulating IKCa1.1, did not affect IBa1.2 but potentiated both high K+- and phenylephrine-induced contractions. Docking and molecular dynamics simulations identified the molecular basis supporting the different activity of dynasore and dyngo-4a at CaV1.2 and KCa1.1 channels. Mito-tempol only partially counteracted the effects of dynasore and dyngo-4a on phenylephrine-induced tone. In conclusion, the present data, along with previous observations (Ahmed et al., 2022) rise caution for the use of dynasore, mdivi-1, and dyngo-4a as tools to investigate the role of mitochondrial fission in vascular contraction: to this end, a selective dynamin inhibitor and/or a different experimental approach are needed.

Artificial intelligence-driven identification of morin analogues acting as CaV1.2 channel blockers: Synthesis and biological evaluation

Morin is a vasorelaxant flavonoid, whose activity is ascribable to Ca_V1.2 channel blockade that, however, is weak as compared to that of clinically used therapeutic agents. A conventional strategy to circumvent this drawback is to synthesize new derivatives differently decorated and, in this context, morin-derivatives able to interact with Ca_V1.2 channels were found by employing the potential of PLATO in target fishing and reverse screening. Three different derivatives (5a-c) were selected as promising tools, synthesized, and investigated in in vitro functional studies using rat aorta rings and rat tail artery myocytes. 5a-c were found more effective vasorelaxant agents than the naturally occurring parent compound and antagonized both electro- and pharmaco-mechanical coupling in an endothelium-independent manner. 5a, the series' most potent, reduced also Ca²⁺ mobilization from intracellular store sites. Furthermore, 5a≈5c > 5b inhibited Ba²⁺ current through Ca_V1.2 channels. However, compound 5a caused also a concentration-dependent inhibition of K_Ca1.1 channel currents.

Novel Labdane Diterpenes-Based Synthetic Derivatives: Identification of a Bifunctional Vasodilator That Inhibits CaV1.2 and Stimulates KCa1.1 Channels

Sesquiterpenes such as leucodin and the labdane-type diterpene manool are natural compounds endowed with remarkably in vitro vasorelaxant and in vivo hypotensive activities. Given their structural similarity with the sesquiterpene lactone (+)-sclareolide, this molecule was selected as a scaffold to develop novel vasoactive agents. Functional, electrophysiology, and molecular dynamics studies were performed. The opening of the five-member lactone ring in the (+)-sclareolide provided a series of labdane-based small molecules, promoting a significant in vitro vasorelaxant effect. Electrophysiology data identified 7 as a Ca_V1.2 channel blocker and a K_Ca1.1 channel stimulator. These activities were also confirmed in the intact vascular tissue. The significant antagonism caused by the Ca_V1.2 channel agonist Bay K 8644 suggested that 7 might interact with the dihydropyridine binding site. Docking and molecular dynamic simulations provided the molecular basis of the Ca_V1.2 channel blockade and K_Ca1.1 channel stimulation produced by 7. Finally, 7 reduced coronary perfusion pressure and heart rate, while prolonging conduction and refractoriness of the atrioventricular node, likely because of its Ca²⁺ antagonism. Taken together, these data indicate that the labdane scaffold represents a valuable starting point for the development of new vasorelaxant agents endowed with negative chronotropic properties and targeting key pathways involved in the pathophysiology of hypertension and ischemic cardiomyopathy.

Vietnamese Dalbergia tonkinensis: A Promising Source of Mono- and Bifunctional Vasodilators

Hypertension is a risk factor for cardiovascular diseases, which are the main cause of morbidity and mortality in the world. In the search for new molecules capable of targeting K_Ca1.1 and Ca_V1.2 channels, the expression of which is altered in hypertension, the in vitro vascular effects of a series of flavonoids extracted from the heartwoods, roots, and leaves of Dalbergia tonkinensis Prain, widely used in traditional medicine, were assessed. Rat aorta rings, tail artery myocytes, and docking and molecular dynamics simulations were used to analyse their effect on these channels. Formononetin, orobol, pinocembrin, and biochanin A showed a marked myorelaxant activity, particularly in rings stimulated by moderate rather than high KCl concentrations. Ba²⁺ currents through Ca_V1.2 channels (I_Ba1.2) were blocked in a concentration-dependent manner by sativanone, 3′-O-methylviolanone, pinocembrin, and biochanin A, while it was stimulated by ambocin. Sativanone, dalsissooside, and eriodictyol inhibited, while tectorigenin 7-O-[β-D-apiofuranosyl-(1→6)-β-D-glucopyranoside], ambocin, butin, and biochanin A increased I_KCa1.1. In silico analyses showed that biochanin A, sativanone, and pinocembrin bound with high affinity in target-sensing regions of both channels, providing insight into their potential mechanism of action. In conclusion, Dalbergia tonkinensis is a valuable source of mono- and bifunctional, vasoactive scaffolds for the development of novel antihypertensive drugs.

2-Hydroxy-5-(3,5,7-trihydroxy-4-oxo-4H-chromen-2-yl)phenyl (E)-3-(4-hydroxy-3-methoxyphenyl)acrylate: Synthesis, In Silico Analysis and In Vitro Pharmacological Evaluation

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.

A multitarget semi-synthetic derivative of the flavonoid morin with improved in vitro vasorelaxant activity: Role of CaV1.2 and KCa1.1 channels

Ca_V1.2 channels play a fundamental role in the regulation of vascular smooth muscle tone. The aim of the present study was to synthesize morin derivatives bearing the nitrophenyl moiety of dihydropyridine Ca²⁺ antagonists to increase the flavonoid vasorelaxant activity. The effects of morin and its derivatives were assessed on Ca_V1.2 and K_Ca1.1 channels, both in vitro and in silico, as well as on the contractile responses of rat aorta rings. All compounds were effective Ca_V1.2 channel blockers, positioning in the α_1C subunit region where standard blockers bind. Among the four newly synthesized morin derivatives, the penta-acetylated morin-1 was the most efficacious Ca²⁺ antagonist, presenting a vasorelaxant profile superior to that of the parent compound and, contrary to morin, antagonized also the release of Ca²⁺ from the sarcoplasmic reticulum; surprisingly, it also stimulated K_Ca1.1 channel current. Computational analysis demonstrated that morin-1 bound close to the K_Ca1.1 channel S6 segment. In conclusion, these findings open a new avenue for the synthesis of valuable multi-functional, vasorelaxant morin derivatives capable to target several pathways underpinning the pathogenesis of hypertension.

Design, synthesis and pharmacological evaluation of ester-based quercetin derivatives as selective vascular KCa1.1 channel stimulators

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_Ca1.1 channels contributes to its vasorelaxant activity, which is, however, counteracted in part by its concomitant stimulation of Ca_V1.2 channels. Therefore, several quercetin hybrid derivatives were designed and synthesized to produce a more selective K_Ca1.1 channel stimulator, then assessed both in silico and in vitro. All the derivatives interacted with the K_Ca1.1 channel with similar binding energy values. Among the selected derivatives, 1E was a weak vasodilator, though displaying an interesting Ca_V1.2 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_Ca1.1 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_V1.2 channels or enhance its K_Ca1.1 channel stimulatory activity, thus opening new avenues for the synthesis of efficacious vasorelaxant quercetin hybrids.

Fine tuning by protein kinases of CaV1.2 channel current in rat tail artery myocytes

Seventeen compounds, rather selective, direct or indirect inhibitors and activators of PKA, PKG, and PKC, were analysed for effects on vascular Ca_V1.2 channel current (I_Ca1.2) by using the patch-clamp technique in single rat tail artery myocytes. The aim was to investigate how PKs regulate I_Ca1.2 and disclose any unexpected modulation of Ca_V1.2 channel function by these agents. The cAMP analogues 8-Br-cAMP and 6-Bnz-cAMP partially reduced I_Ca1.2 in dialysed cells, while weakly increasing it under the perforated configuration. The β-adrenoceptor agonist isoproterenol and the adenylate cyclase activator forskolin concentration-dependently increased I_Ca1.2; this effect was reversed by PKA inhibitors H-89 and KT5720, but not by PKI 6-22. The cGMP analogue 8-Br-cGMP, similarly to the NO-donor SNP, moderately reduced I_Ca1.2, this effect being reversed to a slight stimulation under the perforated configuration. Among PKG inhibitors, Rp-8-Br-PET-cGMPS decreased current amplitude in a concentration-dependent manner while Rp-8-Br-cGMPS was ineffective. The non-specific phosphodiesterase inhibitor IBMX increased I_Ca1.2, while H-89, KT5720, and PKI 6-22 antagonized this effect. The PKC activator PMA, but not the diacylglycerol analogue OAG, stimulated I_Ca1.2 in a concentration-dependent manner; conversely, the PKCα inhibitor Gö6976 markedly reduced basal I_Ca1.2 and, similarly to the PKCδ (rottlerin) and PKCε translocation inhibitors antagonised PMA-induced current stimulation. The ensemble of findings indicates that the stimulation of cAMP/PKA, in spite of the paradoxical effect of both 8-Br-cAMP and 6-Bnz-cAMP, or PKC pathways enhanced, while that of cGMP/PKG weakly inhibited I_Ca1.2 in rat tail artery myocytes. Since Rp-8-Br-PET-cGMPS and Gö6976 appeared to block directly Ca_V1.2 channel, their docking to the channel protein was investigated. Both compounds appeared to bind the α_1C subunit in a region involved in Ca_V1.2 channel inactivation, forming an interaction network comparable to that of Ca_V1.2 channel blockers. Therefore, caution should accompany the use of these agents as pharmacological tools to elucidate the mechanism of action of drugs on vascular preparations.

Ritanserin blocks CaV1.2 channels in rat artery smooth muscles: electrophysiological, functional, and computational studies

Ca_V1.2 channel blockers or 5-HT₂ receptor antagonists constitute effective therapy for Raynaud’s syndrome. A functional link between the inhibition of 5-HT₂ receptors and Ca_V1.2 channel blockade in arterial smooth muscles has been hypothesized. Therefore, the effects of ritanserin, a nonselective 5-HT₂ receptor antagonist, on vascular Ca_V1.2 channels were investigated through electrophysiological, functional, and computational studies. Ritanserin blocked Ca_V1.2 channel currents (I_Ca1.2) in a concentration-dependent manner (K_r = 3.61 µM); I_Ca1.2 inhibition was antagonized by Bay K 8644 and partially reverted upon washout. Conversely, the ritanserin analog ketanserin (100 µM) inhibited I_Ca1.2 by ~50%. Ritanserin concentration-dependently shifted the voltage dependence of the steady-state inactivation curve to more negative potentials (K_i = 1.58 µM) without affecting the slope of inactivation and the activation curve, and decreased I_Ca1.2 progressively during repetitive (1 Hz) step depolarizations (use-dependent block). The addition of ritanserin caused the contraction of single myocytes not yet dialyzed with the conventional method. Furthermore, in depolarized rings, ritanserin, and to a lesser extent, ketanserin, caused a concentration-dependent relaxation, which was antagonized by Bay K 8644. Ritanserin and ketanserin were docked at a region of the Ca_V1.2 α_1C subunit nearby that of Bay K 8644; however, only ritanserin and Bay K 8644 formed a hydrogen bond with key residue Tyr-1489. In conclusion, ritanserin caused in vitro vasodilation, accomplished through the blockade of Ca_V1.2 channels, which was achieved preferentially in the inactivated and/or resting state of the channel. This novel activity encourages the development of ritanserin derivatives for their potential use in the treatment of Raynaud’s syndrome.

Aberrant Exon 8/8a Splicing by Downregulated PTBP (Polypyrimidine Tract-Binding Protein) 1 Increases CaV1.2 Dihydropyridine Resistance to Attenuate Vasodilation

OBJECTIVE

Calcium channel blockers, such as dihydropyridines, are commonly used to inhibit enhanced activity of vascular Ca_V1.2 channels in hypertension. However, patients who are insensitive to such treatments develop calcium channel blocker-resistant hypertension. The function of Ca_V1.2 channel is diversified by alternative splicing, and the splicing factor PTBP (polypyrimidine tract-binding protein) 1 influences the utilization of mutually exclusive exon 8/8a of the Ca_V1.2 channel during neuronal development. Nevertheless, whether and how PTBP1 makes a role in the calcium channel blocker sensitivity of vascular Ca_V1.2 channels, and calcium channel blocker-induced vasodilation remains unknown. Approach and Results: We detected high expression of PTBP1 and, inversely, low expression of exon 8a in Ca_V1.2 channels (Ca_V1.2_E8a) in rat arteries. In contrast, the opposite expression patterns were observed in brain and heart tissues. In comparison to normotensive rats, the expressions of PTBP1 and Ca_V1.2_E8a channels were dysregulated in mesenteric arteries of hypertensive rats. Notably, PTBP1 expression was significantly downregulated, and Ca_V1.2_E8a channels were aberrantly increased in dihydropyridine-resistant arteries compared with dihydropyridine-sensitive arteries of rats and human. In rat vascular smooth muscle cells, PTBP1 knockdown resulted in shifting of Ca_V1.2 exon 8 to 8a. Using patch-clamp recordings, we demonstrated a concomitant reduction of sensitivity of Ca_V1.2 channels to nifedipine, due to the higher expression of Ca_V1.2_E8a isoform. In vascular myography experiments, small interfering RNA-mediated knockdown of PTBP1 attenuated nifedipine-induced vasodilation of rat mesenteric arteries.

CONCLUSIONS

PTBP1 finely modulates the sensitivities of Ca_V1.2 channels to dihydropyridine by shifting the utilization of exon 8/8a and resulting in changes of responses in dihydropyridine-induced vasodilation.

The Selective Rat Toxicant Norbormide Blocks KATP Channels in Smooth Muscle Cells But Not in Insulin-Secreting Cells

Norbormide is a toxicant selective for rats to which it induces a widespread vasoconstriction. In a recent paper, we hypothesized a role of ATP-sensitive potassium (K_ATP) channels in norbormide-induced vasoconstriction. The current study was undertaken to verify this hypothesis by comparing the effects of norbormide with those of glibenclamide, a known K_ATP channel blocker. The whole-cell patch-clamp method was used to record K_ATP currents in myocytes freshly isolated from the rat and mouse caudal artery and from the rat gastric fundus, as well as in insulin-secreting pancreatic beta cells (INS-1 cells). Smooth muscle contractile function was assessed on either rat caudal artery rings or gastric fundus strips. Molecular modeling and docking simulation to K_ATP channel proteins were investigated in silico. Both norbormide (a racemic mixture of endo and exo isomers) and glibenclamide inhibited K_ATP currents in rat and mouse caudal artery myocytes, as well as in gastric fundus smooth muscle cells. In rat INS-1 cells, only glibenclamide blocked K_ATP channels, whereas norbormide was ineffective. The inhibitory effect of norbormide in rat caudal artery myocytes was not stereo-specific as both the endo isomers (active as vasoconstrictor) and the exo isomers (inactive as vasoconstrictor) had similar inhibitory activity. In rat caudal artery rings, norbormide-induced contraction was partially reverted by the K_ATP channel opener pinacidil. Computational approaches indicated the SUR subunit of K_ATP channels as the binding site for norbormide. K_ATP channel inhibition may play a role in norbormide-induced vasoconstriction, but does not explain the species selectivity, tissue selectivity, and stereoselectivity of its constricting activity. The lack of effect in INS-1 cells suggests a potential selectivity of norbormide for smooth muscle K_ATP channels.

From in silico to in vitro: a trip to reveal flavonoid binding on the Rattus norvegicus Kir6.1 ATP-sensitive inward rectifier potassium channel

Background

ATP-sensitive inward rectifier potassium channels (Kir), are a potassium channel family involved in many physiological processes. K_ATP dysfunctions are observed in several diseases such as hypoglycaemia, hyperinsulinemia, Prinzmetal angina–like symptoms, cardiovascular diseases.

Methods

A broader view of the K_ATP 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 K_ATP 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.

Antimalarial agents against both sexual and asexual parasites stages: structure-activity relationships and biological studies of the Malaria Box compound 1-[5-(4-bromo-2-chlorophenyl)furan-2-yl]-N-[(piperidin-4-yl)methyl]methanamine (MMV019918) and analogues

Therapies addressing multiple stages of Plasmodium falciparum life cycle are highly desirable for implementing malaria elimination strategies. MMV019918 (1, 1-[5-(4-bromo-2-chlorophenyl)furan-2-yl]-N-[(piperidin-4-yl)methyl]methanamine) was selected from the MMV Malaria Box for its dual activity against both asexual stages and gametocytes. In-depth structure-activity relationship studies and cytotoxicity evaluation led to the selection of 25 for further biological investigation. The potential transmission blocking activity of 25 versus P. falciparum was confirmed through the standard membrane-feeding assay. Both 1 and 25 significantly prolonged atrioventricular conduction time in Langendorff-isolated rat hearts, and showed inhibitory activity of Ba²⁺ current through Ca_v1.2 channels. An in silico target-fishing study suggested the enzyme phosphoethanolamine methyltransferase (PfPMT) as a potential target. However, compound activity against PfPMT did not track with the antiplasmodial activity, suggesting the latter activity relies on a different molecular target. Nevertheless, 25 showed interesting activity against PfPMT, which could be an important starting point for the identification of more potent inhibitors active against both sexual and asexual stages of the parasite.

Gold nanoparticles potentiate CaV channel currents in rat tail artery myocytes

This study was designed to unveil effects of 5-nm sized, polyvinylpyrrolidone-coated gold nanoparticles (AuNPs) on vascular Ca_V1.2 and Ca_V3.1 channels. Ba²⁺ currents through both channels (I_Ba1.2 and I_Ba3.1) were recorded in single myocytes isolated from the rat tail main artery by means of the whole-cell patch-clamp method. AuNPs increased I_Ba1.2 and I_Ba3.1 amplitude in a concentration- and V_h-dependent manner. Neither the voltage dependence of inactivation and activation curves nor inactivation and activation kinetics were affected by AuNPs. In conclusion, these findings warrant further investigation to clarify whether different types of NPs possess the same stimulatory activity and may represent a toxic hazard to humans.

Cav1.2 channel current block by the PKA inhibitor H-89 in rat tail artery myocytes via a PKA-independent mechanism: Electrophysiological, functional, and molecular docking studies

To characterize the role of cAMP-dependent protein kinase (PKA) in regulating vascular Ca²⁺ current through Ca_v1.2 channels [I_Ca1.2], we have documented a marked capacity of the isoquinoline H-89, widely used as a PKA inhibitor, to reduce current amplitude. We hypothesized that the I_Ca1.2 inhibitory activity of H-89 was mediated by mechanisms unrelated to PKA inhibition. To support this, an in-depth analysis of H-89 vascular effects on both I_Ca1.2 and contractility was undertaken by performing whole-cell patch-clamp recordings and functional experiments in rat tail main artery single myocytes and rings, respectively. H-89 inhibited I_Ca1.2 with a pIC₅₀ (M) value of about 5.5, even under conditions where PKA activity was either abolished by both the PKA antagonists KT5720 and protein kinase inhibitor fragment 6-22 amide or enhanced by the PKA stimulators 6-Bnz-cAMP and 8-Br-cAMP. Inhibition of I_Ca1.2 by H-89 appeared almost irreversible upon washout, was charge carrier- and voltage-dependent, and antagonised by the Ca_v1.2 channel agonist (S)-(-)-Bay K 8644. H-89 did not alter both potency and efficacy of verapamil, did not affect current kinetics or voltage-dependent activation, while shifting to the left the 50% voltage of inactivation in a concentration-dependent manner. H-89 docked at the α_1C subunit in a pocket region close to that of (S)-(-)-Bay K 8644 docking, forming a hydrogen bond with the same, key amino acid residue Tyr-1489. Finally, both high K⁺- and (S)-(-)-Bay K 8644-induced contractions of rings were fully reverted by H-89. In conclusion, these results indicate that H-89 inhibited vascular I_Ca1.2 and, consequently, the contractile function through a PKA-independent mechanism. Therefore, caution is recommended when interpreting experiments where H-89 is used to inhibit vascular smooth muscle PKA.

The surge of flavonoids as novel, fine regulators of cardiovascular Cav channels

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_v1.2 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.

Functional, electrophysiological and molecular docking analysis of the modulation of Cav 1.2 channels in rat vascular myocytes by murrayafoline A

BACKGROUND AND PURPOSE

The carbazole alkaloid murrayafoline A (MuA) enhances contractility and the Ca(2+) currents carried by the Cav 1.2 channels [ICa1.2 ] of rat cardiomyocytes. As only few drugs stimulate ICa1.2 , this study was designed to analyse the effects of MuA on vascular Cav 1.2 channels.

EXPERIMENTAL APPROACH

Vascular activity was assessed on rat aorta rings mounted in organ baths. Cav 1.2 Ba(2+) current [IBa1.2 ] was recorded in single rat aorta and tail artery myocytes by the patch-clamp technique. Docking at a 3D model of the rat, α1c central pore subunit of the Cav 1.2 channel was simulated in silico.

KEY RESULTS

In rat aorta rings MuA, at concentrations ≤14.2 μM, increased 30 mM K(+) -induced tone and shifted the concentration-response curve to K(+) to the left. Conversely, at concentrations >14.2 μM, it relaxed high K(+) depolarized rings and antagonized Bay K 8644-induced contraction. In single myocytes, MuA stimulated IBa1.2 in a concentration-dependent, bell-shaped manner; stimulation was stable, incompletely reversible upon drug washout and accompanied by a leftward shift of the voltage-dependent activation curve. MuA docked at the α1C subunit central pore differently from nifedipine and Bay K 8644, although apparently interacting with the same amino acids of the pocket. Neither Bay K 8644-induced stimulation nor nifedipine-induced block of IBa1.2 was modified by MuA.

CONCLUSIONS AND IMPLICATIONS

Murrayafoline A is a naturally occurring vasoactive agent able to modulate Cav 1.2 channels and dock at the α1C subunit central pore in a manner that differed from that of dihydropyridines.

The vasodilator papaverine stimulates L-type Ca(2+) current in rat tail artery myocytes via a PKA-dependent mechanism

Papaverine is an opium alkaloid, primarily used as an antispasmodic drug and as a cerebral and coronary vasodilator. Its phosphodiesterase inhibitory activity promotes increase of cAMP levels mainly in the cytosol. As cAMP is known to modulate L-type Ca(2+) channel activity, here we tested the proposition that papaverine could affect vascular channel function. An in-depth analysis of the effect of papaverine on Ba(2+) or Ca(2+) current through L-type Ca(2+) channel [IBa(L) or ICa(L)], performed in rat tail artery myocytes using either the whole-cell or the perforated patch-clamp method, was accompanied by a functional study on rat aorta rings. Papaverine increased current amplitude under both the perforated or whole-cell configuration. Stimulation of the current by papaverine was concentration-, Vh-, frequency-, and charge carrier-dependent, and fully reverted by drug washout. The PKA inhibitor H89, but not the PKG inhibitor Rp-8-Br-cGMPS, antagonised papaverine- as well as IBMX- (another phosphodiesterase inhibitor) induced IBa(L) stimulation. In cells pre-treated with IBMX, application of papaverine failed to increase current amplitude. Papaverine sped up the inactivation kinetics of IBa(L), though only at concentrations ≥ 30 μM, and shifted the voltage dependence of the inactivation curve to more negative potentials. In rings, the vasorelaxing activity of papaverine was enhanced by previous treatment with nifedipine. In conclusion, papaverine stimulates vascular L-type Ca(2+) channel via a PKA-dependent mechanism, thus antagonising its main vasodilating activity.

Playing with opening and closing of heterocycles: using the cusmano-ruccia reaction to develop a novel class of oxadiazolothiazinones, active as calcium channel modulators and P-glycoprotein inhibitors

As a result of the ring-into-ring conversion of nitrosoimidazole derivatives, we obtained a molecular scaffold that, when properly decorated, is able to decrease inotropy by blocking L-type calcium channels. Previously, we used this scaffold to develop a quantitative structure-activity relationship (QSAR) model, and we used the most potent oxadiazolothiazinone as a template for ligand-based virtual screening. Here, we enlarge the diversity of chemical decorations, present the synthesis and in vitro data for 11 new derivatives, and develop a new 3D-QSAR model with recent in silico techniques. We observed a key role played by the oxadiazolone moiety: given the presence of positively charged calcium ions in the transmembrane channel protein, we hypothesize the formation of a ternary complex between the oxadiazolothiazinone, the Ca2+ ion and the protein. We have supported this hypothesis by means of pharmacophore generation and through the docking of the pharmacophore into a homology model of the protein. We also studied with docking experiments the interaction with a homology model of P-glycoprotein, which is inhibited by this series of molecules, and provided further evidence toward the relevance of this scaffold in biological interactions.

Vascular L-type Ca²⁺ channel blocking activity of sulfur-containing indole alkaloids from Glycosmis petelotii

In the search for novel natural compounds endowed with potential antihypertensive activity, a new sulfur-containing indole alkaloid, N-demethylglypetelotine (2), and its known analogue glypetelotine (1), were isolated from the leaves of Glycosmis petelotii. Their structures were established on the basis of spectroscopic evidence. The two alkaloids were assessed for vasorelaxing activity on rat aorta rings and for L-type Ba(2+) current [I(Ba(L))] blocking activity on single myocytes isolated from rat tail artery. Both glypetelotine and N-demethylglypetelotine inhibited phenylephrine-induced contraction with IC50 values of 20 and 50 μM, respectively. The presence of endothelium did not modify their spasmolytic effect. Neither glypetelotine nor N-demethylglypetelotine affected Ca(2+) release from the sarcoplasmic reticulum induced by phenylephrine. The spasmolytic effect of glypetelotine increased with membrane depolarization. In the presence of 60 mM K(+), both compounds inhibited, in a concentration-dependent manner, the contraction induced by cumulative addition of Ca(2+), this inhibition being inversely related to Ca(2+) concentration. Glypetelotine and, less efficiently N-demethylglypetelotine, inhibited I(Ba(L)), the former compound also affecting I(Ba(L)) kinetics. In conclusion, glypetelotine is a novel vasorelaxing agent which antagonizes L-type Ca(2+) channels.