Potassium Channel Activation Is Involved in the Cardiovascular Effects Induced by Freeze Dried Syzygium jambolanum (Lam.) DC Fruit Juice.

This work aimed to explore the cardiovascular effects induced by freeze-dried juice from Syzygium jambolanum (Lam.) DC fruits (JSJ). JSJ presented high polyphenol content and steroids. HPLC analysis revealed that 2,5-dihydroxybenzoic and caffeic acid were present in higher amounts in the JSJ extract. In rat, JSJ induces hypotension and vasodilatation in mesenteric arteries, with or without vascular endothelium. JSJ-mediated vasodilation response against contractions induced with KCl (60 mM) depolarizing solution was significantly lower than the responses induced by JSJ when evaluated against phenylephrine-induced contractions. To investigate the involvement of potassium channels we used Tyrode's solution with KCl (20 mM) or tetraethylammonium (1.0, 3.0, or 5.0 mM). In these conditions JSJ-induced effects were significantly attenuated. To investigate the potassium channel subtypes involved in the response, we used 4-aminopyridine, glibenclamide, BaCl2, and iberiotoxin. In the presence (simultaneous) of different potassium channel blockers we observed a significant attenuation of JSJ-induced effect. Inhibition was also observed when using BaCl2, glibenclamide, or 4-aminopyridine, separately. However, incubation with iberiotoxin did not promote changes in either maximum effect, or potency. We also evidenced a discrete participation of CaV channels in the JSJ-induced vasorelaxant effect. In addition, patch-clamp studies demonstrated that JSJ could activate potassium channels. In conclusion, JSJ promotes hypotension and vasorelaxation in rats, involving, at least, the activation of potassium channels.

Antioxidant and vasorelaxant activities induced by northeastern Brazilian fermented grape skins.

BACKGROUND: In northeastern Brazil, grape pomace has become a potential alternative byproduct because of the recover phenolic compounds from the vinification process. Comparative analyses were performed between lyophilized extract of grape skins from pomace, described as fermented (FGS), and fresh, unfermented (UGS) grape skins to show the relevant brand's composition upon the first maceration in winemaking. METHODS: The use of in vitro testing such as Folin-Ciocalteu's, DPPH free radical scavenger and HPLC methods were performed to evidence antioxidant effect and phenolic compounds. Additionally, vascular reactivity studies were performed in third-order branches of rat superior mesenteric arteries, which were obtained and placed in organ baths containing Krebs-Henseleit solution, maintained at 37 °C, gassed with a mixture of 95% O2 and 5% CO2, and maintained at pH 7.4. The in situ formation of reactive oxygen species (ROS) was evaluated in small mesenteric rings using oxidative fluorescent dihydroethidium dye. RESULTS: We found higher phenolic content and antioxidant activity in FGS when compared to UGS. HPLC analyses identified a significant number of phenolic compounds with antioxidant potential in both samples. The vasorelaxant effect induced by FGS was more potent than that induced by UGS, and the activity was attenuated after removal of vascular endothelium or by blockade of endothelium-derived relaxing factors, such as NO and EDHF. CONCLUSIONS: The FGS extract may be a great source of natural polyphenol products with potent antioxidant effects and endothelium-dependent vasodilatory actions involving NO and EDHF pathways.

Nitric oxide as a target for the hypotensive and vasorelaxing effects induced by (Z)-ethyl 12-nitrooxy-octadec-9-enoate in rats.

The cardiovascular effects induced by a new organic nitrate were investigated in rats. The (Z)-ethyl 12-nitrooxy-octadec-9-enoate (NCOE) was synthesized from ricinoleic acid, the major compound of the castor oil. NCOE induced significant and dose-dependent hypotension and bradycardia in normotensive rats. In rats pretreated with NCOE (60 mg/kg, i.v., once a day) for 4 consecutive days, hypotension induced by the nitrate was similar to that observed in rats that were not pretreated with the compound. The vasorelaxation induced by the compound was concentration-dependent (10(-10)-10(-3) M) in rat mesenteric artery rings, pre-contracted with phenylephrine (1 µM), with or without endothelium. Pre-incubation with PTIO (300 µM), a free radical form of NO (NO) scavenger, attenuated the NCOE vasorelaxation potency. However, in the presence of L-cysteine (3 mM), a reduced form of NO (NO-) scavenger, NCOE response was potentiated. NCOE effect was not changed in the presence of an inhibitor of cytochrome P450, proadifen (10 µM). On the other hand, the vasodilation was reduced in the presence of mitochondrial aldehyde dehydrogenase inhibitor (mtALDH), cyanamide (1 mM); soluble guanylyl cyclase inhibitor (sGC), ODQ (10 µM); and non-selective K+ channels blocker, TEA (3 mM). In addition the NCOE-induced vasorelaxation was reduced by BKCa (iberiotoxin, 100 nM) and KATP selective (glibenclamide, 10 µM) blockers, however the effect was not modified by a KV blocker (4-aminopyridine, 1 mM). Furthermore, NCOE increased NO levels in rat aortic smooth muscle cultured cells, detected by NO-sensitive probe DAF-2DA, by flow cytometry. These results together suggest that NCOE induces short-lasting hypotension and bradycardia, and promotes vasorelaxation due to NO release through the compound metabolism via mtALDH and consequent sGC, KATP and BKCa activation. Furthermore, the compound was not able to induce tolerance.

Participation of nitric oxide pathway in the relaxation response induced by E-cinnamaldehyde oxime in superior mesenteric artery isolated from rats.

For many years, nitric oxide (NO) has been studied as an important mediator in the control of vascular tone. Endothelial deficiencies that diminish NO production can result in the development of several future cardiovascular diseases, such as hypertension and arteriosclerosis. In this context, new drugs with potential ability to donate NO have been studied. In this study, 3 aromatic oximes [benzophenone oxime, 4-Cl-benzophenone oxime, and E-cinnamaldehyde oxime (E-CAOx)] induced vasorelaxation in endothelium-denuded and intact superior mesenteric rings precontracted with phenylephrine. E-CAOx demonstrated the most potent effect, and its mechanism of action was evaluated. Vascular reactivity experiments demonstrated that the effect of E-CAOx was reduced by the presence of 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, 1H[1,2,4,]oxadiazolo[4,3-a]quinoxalin-1-one, and (Rp)-8-(para-chlorophenylthio)guanosine-3',5'-cyclic monophosphorothioate, suggesting the participation of NO/sGC/PKG pathway. NO donation seems to be mediated through nicatinamide adenine dinucleotide phosphate-dependent reductases because 7-ethoxyresorufin decreased the effect of E-CAOx on vascular reactivity and reduced NO formation as detected by flow cytometry using the NO indicator diaminofluorescein 4,5-diacetate. Further downstream of NO donation, K+ subtype channels were also shown to be involved in the E-CAOx vasorelaxant effect. The present study showed that E-CAOx acts like an NO donor, activating NO/sGC/PKG pathway and thus K+ channels.

Warifteine, a bisbenzylisoquinoline alkaloid, induces relaxation by activating potassium channels in vascular myocytes.

The present study used functional and electrophysiological approaches to investigate the mechanisms by which warifteine, a bisbenzylisoquinoline alkaloid isolated from Cissampelos sympodialis Eichl., causes vasorelaxation of the rat thoracic aorta. Warifteine (1 pmol/L-10 µmol/L) induced concentration-dependent relaxation (pD(2) = 9.40 ± 0.06; n = 5) of endothelium-intact aortic rings precontracted with noradrenaline (10-100 µmol/L). The relaxation effects were not attenuated by removal of the endothelium. Warifteine also induced the relaxation of prostaglandin F(2α) (1-10 mmol/L)-precontracted rings (pD(2) = 9.2 ± 0.2; n = 8). In contrast, the relaxant activity of warifteine was nearly abolished in high K(+) (80 mmol/L)-precontracted aortic rings. In preparations incubated with 20 mmol/L KCl or with the K(+) channel blockers tetraethylammonium (1, 3 and 5 mmol/L), iberiotoxin (20 nmol/L), 4-aminopyridine (1 mmol/L) or glibenclamide (10 µmol/L), the vasorelaxant activity of warifteine was markedly reduced. However, BaCl(2) (1 mmol/L) had no effect on the relaxant effects of warifteine. In vascular myocytes, warifteine (100 nmol/L) significantly increased whole-cell K(+) currents (at 70 mV). Under nominally Ca(2+) -free conditions, warifteine did not reduce extracellular Ca(2+) -induced contractions in rings precontracted with high K(+) or noradrenaline (100 µmol/L). Together, the results of the present study indicate that warifteine induces potent concentration-dependent relaxation in the rat aorta via an endothelium-independent mechanism that involves the activation of K(+) channels.

Rotundifolone-induced relaxation is mediated by BK(Ca) channel activation and Ca(v) channel inactivation.

Rotundifolone is the major constituent of the essential oil of Mentha x villosa Hudson. In preliminary studies, rotundifolone induced significant hypotensive, bradycardic and vasorelaxant effects in rats. Thus, to gain more insight into the pharmacology of rotundifolone, the aim of this study was to characterize the molecular mechanism of action involved in relaxation produced by rotundifolone. The relaxant effect was investigated in rat superior mesenteric arteries by using isometric tension measurements and whole-cell patch-clamp techniques. Rotundifolone relaxed phenylephrine-induced contractions in a concentration-dependent manner. Pre-treatment with KCl (20 mM), charybdotoxin (10(-7) M) or tetraethylammonium (TEA 10(-3) or 3 × 10(-3) M) significantly attenuated the relaxation effect induced by rotundifolone. Additionally, whole-cell patch-clamp recordings were made in mesenteric smooth muscle cells and showed that rotundifolone significantly increased K(+) currents, and this effect was abolished by TEA (10(-3) M), suggesting the participation of BK(Ca) channels. Furthermore, rotundifolone inhibited the vasoconstriction induced by CaCl(2) in depolarizing nominally Ca(2+) -free medium and antagonized the contractions elicited by an L-type Ca(2+) channel agonist, S(-)-Bay K 8644 (2 × 10(-7) M), indicating that the vasodilatation involved inhibition of Ca(2+) influx through L-type voltage-dependent calcium channels (Ca(v) type-L). Additionally, rotundifolone inhibited L-type Ca(2+) currents (I(Ca) L), affecting the voltage-dependent activation of I(Ca) L and steady-state inactivation. Our findings suggest that rotundifolone induces vasodilatation through two distinct but complementary mechanisms that clearly depend on the concentration range used. Rotundifolone elicits an increase in the current density of BK(Ca) channels and causes a shift in the steady-state inactivation relationship for Ca(v) type-L towards more hyperpolarized membrane potentials.

Resurgent Na+ current: a new avenue to neuronal excitability control.

Integrative and firing properties are important characteristics of neuronal circuits and these responses are determined in large part by the repertoire of ion channels they express, which can vary considerably between cell types. Recently, a new mode of operation of voltage dependent sodium channels has been described that generates a so-called resurgent Na+ current. Accumulating evidence suggests resurgent Na current participates in the generation of sub-threshold inward Na+ current causing membrane depolarization which provides the necessary drive to fire high-frequency action potentials. Recent studies indicate that resurgent Na+ current could be a more widespread feature than previously thought.