On the mechanisms of the antispasmodic action of some hindered phenols in rat aorta rings

Nutritionally enriched tomatoes (Solanum lycopersicum L.) grown with wood distillate: chemical and biological characterization for quality assessment

Bio-based products are nowadays useful tools able to affect the productivity and quality of conventionally cultivated crops. Several bio-based products are currently on the market; one of the newest and most promising is the wood distillate (WD) derived from the pyrolysis process of waste biomass after timber. Its foliar application has been widely investigated and shown to promote the antioxidant profile of cultivated crops. WD was used here as additive for the cultivation of tomato (Solanum lycopersicum L.) plants. The application improved quality (chemical) parameters, minerals, polyphenols, and lycopene contents of tomato fruits. The extracts of WD-treated and untreated tomatoes have been chemically and biologically characterized. The 1 H-NMR and ESI-mass spectrometry analyses of the extracts revealed the presence of different fatty acids, amino acids and sugars. In particular, the WD-treated tomatoes showed the presence of pyroglutamic acid and phloridzin derivatives, but also dihydrokaempferol, naringenin glucoside, cinnamic acid, and kaempferol-3-O-glucoside. When tested in cells, the extracts showed a promising anti-inflammatory profile in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages. Furthermore, the extracts displayed a slight vasorelaxant activity on rat aorta rings (either endothelium-denuded or endothelium-intact) pre-contracted with phenylephrine or potassium chloride. PRACTICAL APPLICATION: Wood distillate has been used for tomato plant growth. Tomatoes showed improved nutritional parameters, and their extracts displayed antioxidant and anti-inflammatory activities.

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.

Sdox, a H2S releasing anthracycline, with a safer profile than doxorubicin toward vasculature

Sdox is a synthetic H₂S-releasing doxorubicin (Dox) less cardiotoxic and more effective than Dox in pre-clinical, Dox-resistant tumour models. The well-known anthracycline vascular toxicity, however, might limit Sdox clinical use. This study aimed at evaluating Sdox vascular toxicity in vitro, using Dox as reference compound. Both vascular smooth muscle A7r5 and endothelial EA.hy926 cells were more sensitive to Dox than Sdox, although both drugs equally increased intracellular free radical levels. Sdox released H₂S in both cell lines. The H₂S scavenger hydroxocobalamin partially reverted Sdox-induced cytotoxicity in A7r5, but not in EA.hy926 cells, suggesting a role for H₂S in smooth muscle cell death. Markers of Sdox-induced apoptosis were significantly lower than, in A7r5 cells, and comparable to those of Dox in EA.hy926 cells. In A7r5 cells, Dox increased the activity of caspase 3, 8, and 9, Sdox affecting only that of caspase 3. Moreover, both drugs induced comparable DNA damage in A7r5 cells, while Sdox was less toxic than Dox in Ea.hy926 cells. In fresh aorta rings, only Dox weakly increased phenylephrine-induced contraction when endothelium was present. In rings cultured with both drugs for 7 days, Sdox blunted phenylephrine- and high K⁺-induced contractions though at a concentration 10-fold higher than that of Dox. In conclusion, Sdox may represent the prototype of an innovative anthracycline, effective against Dox-resistant tumours, displaying a more favourable vascular toxicity profile compared to the parent compound.

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.

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.

2-Aryl- and 2-amido-benzothiazoles as multifunctional vasodilators on rat artery preparations

The neuroprotective agent riluzole [2-amino-6-(trifluoromethoxy)benzothiazole] has been shown to antagonize neuronal high-voltage activated Ca(2+) currents. In the search for novel scaffolds leading to potential antihypertensive agents, a series of 2-aryl- and 2-amido-benzothiazoles (HUP) were assessed for their vasorelaxing property on rat aorta rings and for their L-type Ba(2+) currents [I(Ba(L))] blocking activity on single myocytes isolated from the rat tail artery. HUP5 and HUP30, the most potent of the series, inhibited phenylephrine-induced contraction with IC₅₀ values in the range 3-6 µM. The presence of endothelium did not modify their spasmolytic activity. Both HUP5 and HUP30 increased tissue levels of cGMP and shifted to the left the concentration-response curve to sodium nitroprusside. In rings precontracted by phenylephrine, tetraethylammonium or 1H-[1,2,4] oxadiazolo [4,3-a] quinoxalin-1-one (ODQ) shifted to the right the concentration-relaxation curves of HUP5 and HUP30. The antispasmodic effect of HUP5 and HUP30 was more marked on rings stimulated with 25/30 mM than with 60 mM K(+). HUP5 and HUP30 antagonized both extracellular Ca(2+) influx and Ca(2+) mobilization from intracellular stores in response to phenylephrine: this effect was not modified by the presence of ODQ. I(Ba(L)) was partly inhibited by HUP5 and blocked by HUP30 in a concentration-dependent as well as ODQ-independent manner. In conclusion, HUP5 and HUP30 are vasorelaxing agents that stimulate soluble guanylyl cyclase, activate K(+) channels, and block extracellular Ca(2+) influx. The present benzothiazole derivatives form a novel class of multifunctional vasodilators which may give rise to effective antihypertensive agents.

The novel potent multidrug resistance inhibitors N,N-bis(cyclohexanol)amine aryl esters are devoid of vascular effects

The aim of this study was to investigate the effects of the four isomers (3a, 3b, 3c and 3d) of a novel multidrug resistance-reverting agent - 3,4,5-trimethoxybenzoic acid 4-(methyl-{4-[3-(3,4,5-trimethoxyphenyl)acryloyloxy]cyclohexyl}amino)cyclohexyl ester - on vascular functions in vitro. A comparison of their mechanical and electrophysiological actions in rat aorta rings and single rat tail artery myocytes, respectively, was performed. In rat aorta rings, 3a-d antagonized both 60 mmol/l K(+)- and phenylephrine-induced contraction in a concentration-dependent manner, with maximal relaxation values averaging 50% of controls, 3d being the most effective of the series. The vasorelaxing effect was similar either in presence or absence of intact endothelium. In rat tail artery myocytes, out of the four isomers, only 3a consistently inhibited Ba(2+) current through Ca(v)1.2 channels. Our results provide functional evidence that 3a-d are weak vasorelaxing agents, although at concentrations much higher than those effective for multidrug resistance reversion in cancer cells.

Studies on the synthesis and the antimicrobial and antioxidant activities of a novel class of fluorescein-based glycosides

Facile glycosylation of a fluorescein diol derivative with per-O-acetyl/benzoyl sugar derivatives using BF(3)·Et(2)O catalyst resulted in the formation of the expected glycosides in 54-66% yield. The biological screening of the glycosides against different microbes shows good inhibitory activity. The antioxidant activity of the fluorescein-based glycosides shows remarkable inhibition (IC(50) ∼80%).

Vascular myorelaxing activity of isolates from South African Hyacinthaceae partly mediated by activation of soluble guanylyl cyclase in rat aortic ring preparations

The vasorelaxing effect of isolates (compounds 1, 2, 3, and 4 (homoisoflavanones), compound 5 (sesquiterpenoid), compounds 6 and 7 (bufadienolides)) from the South African Hyacinthaceae has been assessed using rat aortic ring preparations. Compounds 2, 3, and 4 inhibited the tonic contraction induced by both 60 mm K+ (K60) and phenylephrine, compound 3 being the most potent. Compounds 5, 6, and 7 caused a modest concentration-dependent relaxation, whereas compound 1 was ineffective. Under K25- or K60-induced depolarization, compound 3 displayed antispasmodic effects not reversed by tetraethylammonium. Under precontraction induced with phenylephrine, compound 3 shifted to the left the concentration-relaxation curves of either isoprenaline or sodium nitroprusside. 1 H-[1,2,4] oxidazolol [4,3-a] quinoxalin-1-one shifted to the right the concentration-relaxation curve of compound 3, while 3′-isobutyl-1-methylxanthine had no effect. In the absence of extracellular Ca2+, compound 3 (estimated pIC50 = 4.66) and ryanodine reduced the response to phenylephrine. Phenylephrine-stimulated influx of extracellular Ca2+ was markedly reduced when tissues were pretreated with compound 3 (pIC50 = 5.14) or nifedipine, but stimulated by ryanodine. Compound 3 partially antagonized the contraction induced by phorbol 12-myristate-13-acetate. To our knowledge, this has been the first account describing the vasodilating activity of homoisoflavonoids: compound 3 proved an effective vasorelaxing agent, partly acting via the activation of soluble guanylyl cyclase.

Mechanisms of the antispasmodic activity of 3,5-di-t-butyl catechol (DTCAT) on rat vascular smooth muscles

In skeletal muscle sarcoplasmic reticulum vesicles, 3,5-di-t-butyl catechol (DTCAT) promotes the release of Ca(2+) through the activation of ryanodine receptor Ca(2+) channels. DTCAT mechanical and electrophysiological effects have now been investigated in rat aorta rings and single tail artery myocytes. Rat aorta rings incubated with either 30 microM ryanodine or 100 microM DTCAT developed tension, which averaged 36% and 7%, respectively, of that induced by phenylephrine. DTCAT reduced concentration-dependently both aorta ring contractions to high K(+) (IC(50)=13.5 microM) and L-type Ba(2+) current (IC(50)=22.0 microM) in isolated myocytes. Tetraethylammonium did not reverse the antispasmodic effect of DTCAT in rings stimulated with either 25 or 60 mM K(+). DTCAT relaxed concentration-dependently phenylephrine-pre-contracted rings with intact endothelium (IC(50)=10.9 microM). This effect was markedly reduced by pre-incubation of rings with 100 microM Nomega-nitro-l-arginine methyl ester. DTCAT antagonised phenylephrine-induced contractions in endothelium-deprived rings, either in the presence or in the absence of ryanodine (IC(50)=18.7 microM and 39.8 microM, respectively). Furthermore, both DTCAT (IC(50)=53.3 microM) and ryanodine reduced significantly the response to phenylephrine in the absence of extracellular Ca(2+). Phenylephrine-stimulated influx of extracellular Ca(2+) was markedly inhibited when tissues were pre-treated with DTCAT (IC(50)=19.0 microM) as well as nifedipine. DTCAT (>100 microM) was also able to antagonise the contractions induced by phorbol 12-myristate, 13-acetate. In conclusion, this is the first demonstration that DTCAT inhibits vascular smooth muscle voltage-operated Ca(2+) channels and promotes the release of endothelial nitric oxide. Ryanodine receptor Ca(2+) channels activation or the impairment of the contractile apparatus by DTCAT seem to play a secondary role in its vascular activity.

Vascular activity of two silicon compounds, ALIS 409 and ALIS 421, novel multidrug-resistance reverting agents in cancer cells

PURPOSE

The aim of this study was to investigate the effects of two novel multidrug-resistance reverting agents, ALIS 409 [1,3-dimethyl-1,3-p-fluorophenyl-1,3(3-morfolinopropyl)-1,3-disiloxan dihydrochloride] and ALIS 421 [1,3-dimethyl-1,3-(4-fluorophenyl)-1,3[3(4-buthyl)-(1-piperazinyl)-propyl]-1,3-disiloxan tetrahydrochloride], on vascular functions in vitro.

EXPERIMENTAL DESIGN

A comparison of their mechanical and electrophysiological actions in rat aorta rings and single rat tail artery myocytes, respectively, was performed.

RESULTS

In endothelium-denuded rat aorta rings, ALIS 409 and ALIS 421 antagonized 60 mM K(+)-induced contraction in a concentration-dependent manner with IC(50) values of 52.2 and 15.5 microM, respectively. ALIS 409 and ALIS 421 inhibited L-type Ca(2+) current recorded in artery myocytes in a concentration-dependent manner with IC(50) values of 6.4 and 5.6 microM, respectively. In rat aorta, ALIS 409 and ALIS 421 antagonized the sustained tonic contraction induced by phenylephrine with IC(50) values of 58.0 and 13.7 microM (endothelium-denuded rings) and of 73.9 and 31.9 microM (endothelium-intact rings), respectively. In endothelium-denuded rings, ryanodine reduced significantly the response to phenylephrine in the absence of extracellular Ca(2+) whereas nifedipine, ALIS 409 or ALIS 421 did not affect it. Phenylephrine-stimulated influx of extracellular Ca(2+) was markedly reduced when tissues were pretreated with ALIS 409, ALIS 421 or nifedipine, and stimulated when they were pretreated with ryanodine. Application of ALIS 409 (up to 100 microM) to intact rat aorta rings failed to induce mechanical responses.

CONCLUSIONS

Our results provide functional evidence that the myorelaxing effect elicited either by ALIS 409 or by ALIS 421 involved mainly the direct blockade of extracellular Ca(2+) influx. This effect, however, took place at concentrations much higher than those effective as modifiers of multidrug resistance in cancer cells.

3,5-di-t-butylcatechol (DTCAT) as an activator of rat skeletal muscle ryanodine receptor Ca2+ channel (RyRC)

In the present study, the effects of 3,5-di-t-butylcatechol (DTCAT) on ryanodine receptor Ca(2+) channel (RyRC) of skeletal muscle sarcoplasmic reticulum (SR) vesicles were investigated, both by monitoring extravesicular Ca(2+) concentration directly with the Ca(2+) indicator dye arsenazo III and by studying the high-affinity [(3)H]ryanodine binding. DTCAT stimulated Ca(2+) release from junctional (terminal cisternae) vesicles in a concentration-dependent manner, with a threshold activating concentration of 30 microM and a pEC(50) value of 3.43+/-0.03 M. The release of Ca(2+) induced by DTCAT was antagonized in a concentration-dependent manner by ruthenium red, thus indicating that RyRC is involved in the mechanism of stimulation. A structure-activity relationship analysis carried out on a limited number of compounds suggested that both hydroxy and t-butyl groups in DTCAT were important for the activation of RyRC. DTCAT inhibited [(3)H]ryanodine binding to SR vesicles with a K(i) of 232.5 microM, thus indicating that it acted directly at the skeletal muscle ryanodine receptor binding site to stimulate Ca(2+) release. In conclusion, the ability of DTCAT to release Ca(2+) from TC vesicles of skeletal muscle is noteworthy in view of its possible use as an alternative compound to either caffeine or halothane for performing the "In vitro contracture test" to diagnose the susceptibility of some patients to develop malignant hyperthermia under particular pharmacological treatments.

L-type Ca2+ channels activation and contraction elicited by myricetin on vascular smooth muscles

The effects of myricetin (3,3',4',5,5',7-hesahydroxyflavone), a natural flavonoid found in edible plants, were studied on vascular smooth muscle L-type Ca(2+) channels by comparing its mechanical, radioligand binding, and electrophysiological properties to those of the Ca(2+) channel agonist (S)-(-)-Bay K 8644. In rat aorta rings, both myricetin and (S)-(-)-Bay K 8644 induced contractile responses, which were dependent upon prior exposure to K(+). At 15 mM K(+) (K15) the pEC(50) values for myricetin and (S)-(-)-Bay K 8644 were 4.43+/-0.03 and 7.92+/-0.13, respectively. Furthermore, the maximum tension response to myricetin was not significantly different from that elicited by either (S)-(-)-Bay K 8644 or K60. The Ca(2+) channel blockers nifedipine, verapamil and diltiazem antagonised and fully reverted myricetin-, (S)-(-)-Bay K 8644- as well as K60-induced contractions. Both myricetin and (S)-(-)-Bay K 8644 potentiated rat aorta ring responses to K(+), shifting the K(+) concentration-response curve to the left. (S)-(-)-Bay K 8644, but not myricetin, inhibited in a concentration-dependent manner (+)-[(3)H]PN200-110 binding in porcine aortic membranes. Electrophysiological recordings from single rat tail artery myocytes, under amphotericin B-perforated as well as conventional methods, showed that both myricetin and (S)-(-)-Bay K 8644 increased L-type Ba(2+) current (I(Ba(L))) and shifted the maximum of the current-voltage relationship by 10 mV in the hyperpolarising direction, without, however, modifying the threshold potential. Furthermore, (S)-(-)-Bay K 8644 accelerated both activation and inactivation kinetics of I(Ba(L)) while myricetin slowed down the activation kinetics. Finally, both (S)-(-)-Bay K 8644 and myricetin slowed down deactivation kinetics of I(Ba(L)). These results suggest that myricetin induces vasoconstriction by activating L-type Ca(2+) channel with similar efficacy but a site of action different to that of (S)-(-)-Bay K 8644.

Synthesis of N-substituted piperazinyl carbamoyl and acetyl derivatives of tetrahydropapaverine: potent antispasmodic agents

The synthesis and structure-activity-relationship (SAR) for a series of N-substituted piperazinyl carbamoyl 7-15 and piperazinyl acetyl 18-26 derivatives of tetrahydropapaverine have been carried out. The general synthetic methods of carbamoyl tetrahydropapaverine analogues involve N-substituted piperazines and carbamoyl imidazole tetrahydropapaverine as starting materials. Another route for synthesizing these compounds, involving the formation of carbamoyl imidazole piperazine has also been explored. Acylation of tetrahydropapaverine followed by substitution with various piperazinyl moities afforded the acetyl tetrahydropapaverine derivatives. Variously substituted piperazines have been used to monitor the effect of electron releasing and electron withdrawing substituents upon the antispasmodic activity of the molecules. Effect of varying electron densities on the antispasmodic activity, by altering the position of these groups on the benzene ring has also been monitored. Pharmacological methods involve the in vitro antispasmodic activity studies on a freshly removed guinea pig ileum using a force displacement transducer amplifier connected to a physiograph. Among the analogues synthesized in the present study, a promising compound 7, a potent muscle relaxant as compared to papaverine has been obtained.

3,5-di-t-butyl-4-hydroxyanisole (DTBHA) activation of rat skeletal muscle sarcoplasmic reticulum Ca(2+)-ATPase

3,5-Di-t-butyl-4-hydroxyanisole (DTBHA) increased in a concentration-dependent manner (calculated pEC(50) = 4.55 +/- 0.18 M) the oxalate-stimulated Ca(2+)-pumping rate of rat skeletal muscle sarcoplasmic reticulum (SR) vesicles. Kinetic analysis of this effect suggested that the activation of SR Ca(2+)-ATPase operated by (DTBHA) was of both mixed and non-competitive type with respect to ATP in the range of concentrations 0.1-0.5 mM and above 1 mM, respectively; furthermore, it was independent of the free Ca(2+) concentrations. This indicated that the enzyme activation took place through the acceleration of the enzyme-substrate complex breakdown. Moreover, it appeared that its target site was cyclopiazonic acid sensitive. The uncommon ability of (DTBHA) to upregulate SR Ca(2+) uptake is of interest in view of its possible use for treating pathological conditions characterised by cell Ca(2+) overload as well as genetic disorders where SR Ca(2+) homeostasis is altered.

Characterization of voltage-gated calcium currents in freshly isolated smooth muscle cells from rat tail main artery

The aim of the present study was to characterize voltage-gated Ca2+ currents in smooth muscle cells freshly isolated from rat tail main artery in the presence of 5 mmol L(-1) external Ca2+. Calcium currents were identified on the basis of their voltage dependencies and sensitivity to nifedipine, Ni2+ and cinnarizine. In the majority of the cells studied, T- and L-type currents were observed, while the remaining cells showed predominantly L-type currents. In the latter group of cells, holding potential change from -50 to either -70 or -90 mV increased the corresponding inward current amplitude while its voltage activation threshold remained unchanged. The steady state inactivation of L-type Ca2+ channels showed half-maximal inactivation at -38 mV. A Ca2+-dependent inactivation was also evident. Nifedipine (3 micromol L(-1)) blocked L-type but not T-type Ca2+ currents. Ni2+ (50 micromol L(-1)) as well as cinnarizine (1 micromol L(-1)) suppressed the nifedipine-resistant, T-type component of the currents. At higher concentrations, both Ni2+ (0.3-1 mmol L(-1)) and cinnarizine (10 micromol L(-1)) blocked the net inward current. Replacement of Ca2+ with 10 mmol L(-)1 Ba2+ significantly increased the amplitude of L-type Ca2+ currents. These results demonstrate that smooth muscle cells freshly isolated from rat tail main artery may be divided into two populations, one expressing both L- and T-type and the other only L-type Ca2+ channels. Furthermore, this report shows that in arterial smooth muscle cells cinnarizine potently inhibited T-type currents at low concentrations (1 micromol L(-1)) but also blocked L-type Ca2+ currents at higher concentrations (10 micromol L(-1)).

2,5-Di-t-butyl-1,4-benzohydroquinone (BHQ) inhibits vascular L-type Ca(2+) channel via superoxide anion generation

The aim of the present study was to investigate the effects of 2,5-di-t-butyl-1,4-benzohydroquinone (BHQ), an inhibitor of the sarco-endoplasmic reticulum Ca(2+)-ATPase (SERCA), on the whole-cell voltage-dependent L-type Ca(2+) current (I(Ca(L))) of freshly isolated smooth muscle cells from the rat tail artery using the patch-clamp technique. BHQ, added to the perfusion solution, reduced I(Ca(L)) in a concentration- (IC(50)=66.7 microM) and voltage-dependent manner. This inhibition was only partially reversible. BHQ shifted the voltage dependence of the steady-state inactivation curve to more negative potentials by 7 mV in the mid-potential of the curve, without affecting the activation curve as well as the time course of I(Ca(L)) inactivation. Preincubation of the cells either with 10 microM cyclopiazonic acid, a SERCA inhibitor, or with 3 mM diethyldithiocarbamate, an inhibitor of intracellular superoxide dismutase (SOD), did not modify BHQ inhibition of I(Ca(L)). On the contrary, this effect was no longer evident when SOD (250 u ml(-1)) was added to the perfusion medium. Either in the presence or in the absence of cells, BHQ gave rise to superoxide anion formation, which was markedly inhibited by the addition of SOD. These results indicate that, at micromolar concentrations, BHQ inhibits vascular I(Ca(L)) by giving rise to the formation of superoxide anion which in turn impairs the channel function.

Effects of some sterically hindered phenols on whole-cell Ca(2+) current of guinea-pig gastric fundus smooth muscle cells

1. The aim of the present study was to investigate the effects of extracellular application of some sterically-hindered phenols, namely 3-t-butyl-4-hydroxyanisole (BHA), 3,5-di-t-butyl-4-hydroxyanisole (DTBHA) and the dimer of BHA, 2,2'-dihydroxy-3,3'-di-t-butyl-5,5'-dimethoxydiphenyl (DIBHA), on the whole-cell Ca(2+) current (I(Ca)) of freshly isolated smooth muscle cells from the guinea-pig gastric fundus, in the presence of a range of Ca(2+) concentrations (1 -- 5 mM) using the patch-clamp technique. The influx of Ca(2+) had characteristics of L-type I(Ca) (I(Ca(L))). 2. BHA as well as DTBHA inhibited I(Ca(L)) in a concentration-dependent manner, during depolarization to 10 mV from a holding potential of -50 mV. Bath application of BHA (50 microM) and DTBHA (30 microM) decreased I(Ca(L)) by 48.9% and 45.2%, respectively. This inhibition was only partially reversible. In contrast, DIBHA (up to 50 microM) was devoided of effects on I(Ca(L)). 3. BHA inhibition of I(Ca(L)) was voltage-dependent and inversely related to the external concentration of Ca(2+). On the other hand, DTBHA inhibition was only voltage-dependent. 4. BHA and DTBHA shifted the voltage range of the steady-state inactivation curve to more negative potentials by 8 mV at the mid-potential of the curve, without affecting the activation curve. Furthermore, BHA and DTBHA did not modify the time-course of the current decay. 5. We conclude that the inhibition of I(Ca(L)) by BHA and DTBHA is qualitatively similar to that of a Ca(2+) channel blocker and is characterized by the stabilizing effect of the inactivated state of the channel.

Synthesis and antiperoxidant activity of new phenolic O-glycosides

We describe the synthesis of some 3-tert-butyl-4-hydroxyphenyl D-glycopyranosides by reaction of tert-butylhydroquinone with beta-D-pentaacetyl-glucose, beta-D-pentaacetyl-galactose, 2-acetamido- and 3,4,6-tri-O-acetyl-2-butanamido-2-deoxy-beta-D-glucopyranosyl chlorides as well as the formation of anomeric 3-tert-butyl-4-hydroxyphenyl 4,6-di-O-acetyl-2,3-dideoxy-D-erythro-hex-2-eno-pyranosides by reaction between tert-butylhydroquinone and 3,4,6-tri-O-acetyl-D-glucal. All compounds, except 3-tert-butyl-4-hydroxyphenyl alpha- and beta-D-glucopyranosides, inhibited lipid peroxidation with a degree of potency comparable to that of tert-butyl hydroxyanisole.