Channel Inhibitor 4-aminopyridine Research Articles

Vasorelaxant mechanisms of the antidiabetic anagliptin in rabbit aorta: roles of Kv channels and SERCA pump.

The present study investigated the vasorelaxant mechanisms of an oral antidiabetic drug, anagliptin, using phenylephrine (Phe)-induced pre-contracted rabbit aortic rings. Arterial tone measurement was performed in rabbit thoracic aortic rings. Anagliptin induced vasorelaxation in a dose-dependent manner. Pre-treatment with the classical voltagedependent K+ (Kv) channel inhibitors 4-aminopyridine and tetraethylammonium significantly decreased the vasorelaxant effect of anagliptin, whereas pre-treatment with the inwardly rectifying K+ (Kir) channel inhibitor Ba2+, the ATP-sensitive K+ (KATP) channel inhibitor glibenclamide, and the large-conductance Ca2+-activated K+ (BKCa) channel inhibitor paxilline did not attenuate the vasorelaxant effect. Furthermore, the vasorelaxant response of anagliptin was effectively inhibited by pre-treatment with the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) pump inhibitors thapsigargin and cyclopiazonic acid. Neither cAMP/protein kinase A (PKA)-related signaling pathway inhibitors (adenylyl cyclase inhibitor SQ 22536 and PKA inhibitor KT 5720) nor cGMP/protein kinase G (PKG)-related signaling pathway inhibitors (guanylyl cyclase inhibitor ODQ and PKG inhibitor KT 5823) reduced the vasorelaxant effect of anagliptin. Similarly, the anagliptin-induced vasorelaxation was independent of the endothelium. Based on these results, we suggest that anagliptin-induced vasorelaxation in rabbit aortic smooth muscle occurs by activating Kv channels and the SERCA pump, independent of other vascular K+ channels, cAMP/PKA- or cGMP/PKG-related signaling pathways, and the endothelium.

Sensitive Detection of Ciguatoxins Using a Neuroblastoma Cell-Based Assay with Voltage-Gated Potassium Channel Inhibitors.

Ciguatoxins (CTXs) are neurotoxins responsible for ciguatera poisoning (CP), which affects more than 50,000 people worldwide annually. The development of analytical methods to prevent CP is a pressing global issue, and the N2a assay is one of the most promising methods for detecting CTXs. CTXs are highly toxic, and an action level of 0.01 μg CTX1B equivalent (eq)/kg in fish has been proposed. It is desirable to further increase the detection sensitivity of CTXs in the N2a assay to detect such low concentrations reliably. The opening of voltage-gated sodium channels (NaV channels) and blocking of voltage-gated potassium channels (KV channels) are thought to be involved in the toxicity of CTXs. Therefore, in this study, we developed an assay that could detect CTXs with higher sensitivity than conventional N2a assays, using KV channel inhibitors as sensitizing reagents for N2a cells. The addition of the KV channel inhibitors 4-aminopyridine and tetraethylammonium chloride to N2a cells, in addition to the traditional sensitizing reagents ouabain and veratridine, increased the sensitivity of N2a cells to CTXs by up to approximately 4-fold. This is also the first study to demonstrate the influence of KV channels on the toxicity of CTXs in a cell-based assay.

Can Ag+ Permeate through a Potassium Ion Channel? A Bottom-Up Approach by Infrared Spectroscopy of the Ag+ Complex with the Partial Peptide of a Selectivity Filter.

Silver and silver ions have a long history of antimicrobial activity and medical applications. Nevertheless, the activity of Ag+ against bacteria, how it enters a cell, has not yet been established. The K+ channel, a membrane protein, is a possible route. The addition of a channel inhibitor (4-aminopyridine) to modulate the Ag+ uptake could support this view. However, the inhibitor enhances the uptake of Ag+, the opposite result. We have applied cold ion trap infrared laser spectroscopy to complexes of Ag+ and Ac-Tyr-NHMe (a model for GYG) which is a portion of the selectivity filter in the K+ channel to consider the question of permeation. With support from quantum chemical calculations, we have determined the stable conformations of the complex. The conformations strongly suggest that Ag+ would not readily permeate the K+ channel. The mechanism of the unexpected enhancement by the inhibitor is discussed.

Combined Treatment with KV Channel Inhibitor 4-Aminopyridine and either γ-Cystathionine Lyase Inhibitor β-Cyanoalanine or Epinephrine Restores Blood Pressure, and Improves Survival in the Wistar Rat Model of Anaphylactic Shock.

Simple SummaryAllergic diseases are presenting a constant increase all over the world and caused by such different substances as food, drugs, and pollens. Anaphylactic shock is the more severe complication of allergy which can induce death if the treatment is not administered immediately. Some patients do not respond to the recommended treatment, intra venous or intramuscular epinephrine. The pathophysiology of anaphylactic shock is still under investigation. The mediators released after the activation of mast cells and basophiles act on endothelial cells and smooth muscle cells, inducing the vasodilation responsible for hypotension and shock. Nitric oxide and hydrogen sulphide are both intracellular mediators that induce vasodilation. The role of potassium voltage dependent channels is suspected. We aimed to demonstrate the ability of a blocker of potassium voltage dependent channels, 4-aminopyridine, alone or in combination with inhibitors of cystathionine γ-lyase to restore blood pressure and improve survival in an ovalbumin rat anaphylactic shock model. The blockade of potassium voltage dependent channels alone or combined with inhibitors of cystathionine γ-lyase, dl-propargylglycine, or β-cyanoalanine restored blood pressure and improved survival. These findings suggest possible investigative treatment pathways for research concerning epinephrine-refractory anaphylactic shock in patients.The mechanism of anaphylactic shock (AS) remains incompletely understood. The potassium channel blocker 4-aminopyridine (4-AP), the inhibitors of cystathionine γ-lyase (ICSE), dl-propargylglycine (DPG) or β-cyanoalanine (BCA), and the nitric oxide (NO) synthase produce vasoconstriction and could be an alternative for the treatment of AS. The aim of this study was to demonstrate the ability of L-NAME, ICSE alone or in combination with 4-AP to restore blood pressure (BP) and improve survival in ovalbumin (OVA) rats AS. Experimental groups included non-sensitized Wistar rats (n = 6); AS (n = 6); AS (n = 10 per group) treated i.v. with 4-AP (AS+4-AP), epinephrine (AS+EPI), AS+DPG, AS+BCA, or with L-NAME (AS+L-NAME); or AS treated with drug combinations 4-AP+DPG, 4-AP+BCA, 4-AP+L-NAME, or 4-AP+EPI. AS was induced by i.v. OVA (1 mg). Treatments were administered i.v. one minute after AS induction. Mean arterial BP (MAP), heart rate (HR), and survival were monitored for 60 min. Plasma levels of histamine, prostaglandin E2 (PGE2) and F2 (PGF2α), leukotriene B4 and C4, angiotensin II, vasopressin, oxidative stress markers, pH, HCO3, PaO2, PaCO2, and K+ were measured. OVA induced severe hypotension and all AS rats died. Moreover, 4-AP, 4-AP+EPI, or 4-AP+BCA normalized both MAP and HR and increased survival. All sensitized rats treated with 4-AP alone or with 4-AP+BCA survived. The time-integrated MAP “area under the curve” was significantly higher after combined 4-AP treatment with ICSE. Metabolic acidosis was not rescued and NO, ICSE, and Kv inhibitors differentially alter oxidative stress and plasma levels of anaphylactic mediators. The AS-induced reduction of serum angiotensin II levels was prevented by 4-AP treatment alone or in combination with other drugs. Further, 4-AP treatment combined with EPI or with BCA also increased serum PGF2α, whereas only the 4-AP+EPI combination increased serum LTB4. Serum vasopressin and angiotensin II levels were increased by 4-AP treatment alone or in combination with other drugs. Moreover, 4-AP alone and in combination with inhibition of cystathionine γ-lyase or EPI normalizes BP, increases serum vasoconstrictor levels, and improves survival in the Wistar rat model of AS. These findings suggest possible investigative treatment pathways for research into epinephrine-refractory anaphylactic shock in patients.

The antidiabetic drug teneligliptin induces vasodilation via activation of PKG, Kv channels, and SERCA pumps in aortic smooth muscle

Diabetes mellitus (DM) is a metabolic disease closely related to cardiovascular disease. The dipeptidyl peptidase-4 inhibitor teneligliptin is used to treat DM and has recently been shown to have a cardiovascular protective effect against diseases such as hypertension and heart failure. The present study demonstrates the vasodilatory effect of teneligliptin using aortic rings pre-contracted with phenylephrine. Teneligliptin induced a vasodilatory effect in a dose-dependent manner, with and without endothelium. In addition, pretreatment with the nitric oxide synthase inhibitor L-NAME and small-conductance Ca2+-activated K+ channel inhibitor apamin did not alter the teneligliptin-induced vasodilatory effect. Although the adenylyl cyclase inhibitor SQ 22536 and protein kinase A (PKA) inhibitor KT 5720 did not modulate the vasodilatory effect of teneligliptin, the guanylyl cyclase inhibitor ODQ and protein kinase G (PKG) inhibitor KT 5823 effectively reduced the effect of teneligliptin. Similarly, pretreatment with the voltage-dependent K+ (Kv) channel inhibitor 4-aminopyridine (4-AP) also reduced teneligliptin-induced vasodilation. However, pretreatment with the inward rectifier K+ (Kir) channel inhibitor Ba2+, large-conductance Ca2+-activated K+ (BKCa) channel inhibitor paxilline, and ATP-sensitive K+ (KATP) channel inhibitor glibenclamide did not alter the vasodilatory effect of teneligliptin. Our data suggest that Kv7.X, but not Kv1.5 or Kv2.1, is one of the major Kv subtypes involved in teneligliptin-induced vasodilation. Furthermore, pretreatment with the sarcoplasmic/endoplasmic reticulum Ca2+-ATPase (SERCA) pump inhibitor thapsigargin and CPA inhibited the vasodilation induced by teneligliptin. Our results suggest that teneligliptin-induced vasodilation occurs via activation of PKG, SERCA pumps and Kv channels, but not the PKA signaling pathway, other K+ channels, or endothelium.

Antidiabetic omarigliptin dilates rabbit aorta by activating voltage-dependent K+ channels and the sarco/endoplasmic reticulum Ca2+ -ATPase pump.

We investigated the vasodilatory effect of omarigliptin, an oral antidiabetic drug in the dipeptidyl peptidase-4 inhibitor class, and its related mechanisms using phenylephrine (Phe)-induced pre-contracted aortic rings. Omarigliptin dilated aortic rings pre-constricted with Phe in a dose-dependent manner. Pretreatment with the voltage-dependent K+ channel inhibitor 4-aminopyridine significantly attenuated the vasodilatory effect of omarigliptin, whereas pretreatment with the inwardly rectifying K+ channel inhibitor Ba2+ , ATP-sensitive K+ channel inhibitor glibenclamide, and large-conductance Ca2+ -activated K+ channel inhibitor paxilline did not alter its vasodilation. Pretreatment with the sarco/endoplasmic reticulum Ca2+ -ATPase (SERCA) pump inhibitors thapsigargin and cyclopiazonic acid significantly reduced the vasodilatory effect of omarigliptin. Neither cAMP/PKA-related signaling pathway inhibitors nor cGMP/PKG-related signaling pathway inhibitors modulated the vasodilatory effect of omarigliptin. Removal of endothelium did not diminish the vasodilatory effect of omarigliptin. Furthermore, pretreatment with the nitric oxide synthase inhibitor L-NAME or small-conductance Ca2+ -activated K+ channel inhibitor apamin, together with the intermediate-conductance Ca2+ -activated K+ channel inhibitor TRAM-34, did not influence the vasodilatory effect of omarigliptin. In conclusion, omarigliptin induced vasodilation in rabbit aortic smooth muscle by activating voltage-dependent K+ channels and the SERCA pump independently of other K+ channels, cAMP/PKA- and cGMP/PKG-related signaling pathways, and the endothelium.

15-hydroxy eicosadienoic acid is an exacerbating factor for nasal congestion in mice.

Allergic rhinitis (AR) is one of the most common allergic inflammatory diseases worldwide. In AR, increased blood flow and vascular permeability in nasal mucosa cause rhinorrhea and nasal congestion. We investigated the role of an 11Z,14Z-eicosadienoic acid-derived metabolite, 15-hydroxy-11Z,13Z-eicosadienoic acid (15-HEDE), in functional changes in vasculature and nasal congestion in AR. Repeated intranasal administration of Ovalbumin (OVA) caused AR symptoms, such as sneezing and nasal congestion, in mice. OVA administration increased the level of 15-HEDE in nasal lavage fluid, which reached approximately 0.6ng/ml after ten OVA treatments. Upon measuring vascular contraction, treatment with 0.1-3μM 15-HEDE did not cause contraction in mouse aortae, while it dilated aortae that were pre-contracted by thromboxane receptor stimulation. Pretreatment with the voltage-gated K+ (KV ) channel inhibitor 4-aminopyridine significantly inhibited the 15-HEDE-induced vascular relaxation. Intravital imaging showed that administration of 1μg 15-HEDE dilated blood vessels, and Mile's assay demonstrated that this administration also caused dye leakage, indicating vascular hyperpermeability in mouse ears. Computed tomography scanning and morphological study revealed that administration of 3μg 15-HEDE narrowed nasal passages and thickened nasal mucosa in mice. Finally, we confirmed that treating mice with 3μg 15-HEDE caused rhinitis symptoms, such as abdominal breathing, and reduced respiratory frequency, suggesting nasal congestion. 15-HEDE caused vasodilation by activating KV channels and increased vascular permeability, which may lead to nasal congestion. Furthermore, 15-HEDE might be a new lipid mediator that exacerbates nasal congestion in AR.

The anti-diabetic drug trelagliptin induces vasodilation via activation of Kv channels and SERCA pumps

AimsIn this study, we investigated the vasodilatory effects of trelagliptin (a dipeptidyl peptidase-4 inhibitor) and its related mechanisms using rabbit aortic rings. Main methodsArterial tone measurement was performed in rabbit thoracic aortic rings. Key findingsTrelagliptin induced vasodilation in a dose-dependent manner. Pretreatment with the ATP-sensitive K+ channel inhibitor glibenclamide, large-conductance Ca2+-activated K+ channel inhibitor paxilline, and inwardly rectifying K+ channel inhibitor Ba2+ did not affect the vasodilatory effect of trelagliptin. However, pretreatment with the voltage-dependent K+ (Kv) channel inhibitors 4-aminopyridine and tetraethylammonium significantly attenuated the vasodilatory effect of trelagliptin, suggesting that the vasodilatory effect of trelagliptin is associated with Kv channel activation. Although pretreatment with Kv1.5 and Kv2.1 subtype inhibitors did not affect the response to trelagliptin, pretreatment with a Kv7.X subtype inhibitor effectively reduced the vasodilatory effect of trelagliptin. Furthermore, sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) pump inhibitors also significantly attenuated the vasodilatory effect of trelagliptin. These effects, however, were not affected by pretreatment with Ca2+ channel inhibitors, adenylyl cyclase/PKA inhibitors, guanylyl cyclase/PKG inhibitors, or removal of the endothelium. SignificanceFrom these results, we concluded that the vasodilatory effect of trelagliptin was associated with the activation of Kv channels (primary the Kv7.X subtype) and SERCA pump regardless of other K+ channels, Ca2+ channels, cAMP/PKA-related or cGMP/PKG-related signaling pathways, and the endothelium. Therefore, caution is required when prescribing trelagliptin to the patients with hypotension and diabetes.

The anti-diabetic drug alogliptin induces vasorelaxation via activation of Kv channels and SERCA pumps

In the present study, we investigated the vasorelaxant effects of alogliptin, an oral antidiabetic drug in the dipeptidyl peptidase-4 (DPP-4) inhibitor class, using phenylephrine (Phe)-induced pre-contracted aortic rings. Alogliptin induced vasorelaxation in a dose-dependent manner. Pre-treatment with the voltage-dependent K+ (Kv) channel inhibitor 4-aminopyridine (4-AP) significantly decreased the vasorelaxant effect of alogliptin, whereas pre-treatment with the inwardly rectifying K+ (Kir) channel inhibitor Ba2+, ATP-sensitive K+ (KATP) channel inhibitor glibenclamide, and large-conductance Ca2+-activated K+ (BKCa) channel inhibitor paxilline did not alter the effects of alogliptin. Although pre-treatment with the Ca2+ channel inhibitor nifedipine did not affect the vasorelaxant effect of alogliptin, pre-treatment with the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) pump inhibitors thapsigargin and cyclopiazonic acid effectively attenuated the vasorelaxant response of alogliptin. Neither cGMP/protein kinase G (PKG)-related signaling pathway inhibitors (guanylyl cyclase inhibitor ODQ and PKG inhibitor KT 5823) nor cAMP/protein kinase A (PKA)-related signaling pathway inhibitors (adenylyl cyclase inhibitor SQ 22536 and PKA inhibitor KT 5720) reduced the vasorelaxant effect of alogliptin. Similarly, the vasorelaxant effect of alogliptin was not changed by endothelium removal or pre-treatment with the nitric oxide (NO) synthase inhibitor L-NAME or the small- and intermediate-conductance Ca2+-activated K+ (SKCa and IKCa) channel inhibitors apamin and TRAM-34. Based on these results, we suggest that alogliptin induced vasorelaxation in rabbit aortic smooth muscle by activating Kv channels and the SERCA pump independent of other K+ channels, cGMP/PKG-related or cAMP/PKA-related signaling pathways, and the endothelium.

Participation of the opioid receptor - nitric oxide - cGMP - K+ channel pathway in the peripheral antinociceptive effect of nalbuphine and buprenorphine in rats.

The aim of this study was to examine if the peripheral antinociceptive effects of the opioid agonist/antagonist nalbuphine and buprenorphine involve the sequential participation of nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) synthesis followed by K+ channel opening in the formalin test. Wistar rats (180-220 g) were injected in the dorsal surface of the right hind paw with formalin (1%). Rats received a subcutaneous (s.c.) injection into the dorsal surface of the paw of vehicles or increasing doses of nalbuphine (50-200 μg/paw) or buprenorphine (1-5 μg/paw) 20 min before formalin injection into the paw. Nalbuphine antinociception was reversed by the s.c. injection into the paw of the inhibitor of NO synthesis (NG-nitro-l-arginine methyl ester (L-NAME)), by the inhibitor of guanylyl cyclase (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ)), by the Kir6.1-2, ATP-sensitive K+ channel inhibitors (glibenclamide and glipizide), by the KCa2.1-3, small conductance Ca2+-activated K+ channel blocker (apamin), by the KCa1.1, large conductance Ca2+-activated K+ channel blocker (charybdotoxin), and by the KV, voltage-dependent K+ channel inhibitors (4-aminopyridine (4-AP) and tetraethylammonium chloride (TEA)). The antinociceptive effect produced by buprenorphine was blocked by the s.c. injection of 4-AP and TEA but not by L-NAME, ODQ, glibenclamide, glipizide, apamin, or charybdotoxin. The present results provide evidence for differences in peripheral mechanisms of action between these opioid drugs.

Propofol Relaxes Isolated Rat Aorta through BKCa Activation

Propofol is an intravenous anesthetic that can be used for the induction and maintenance of anesthesia. In the present study, it was aimed to investigate the mechanism of vasodilator action of propofol in the rat aorta (RA). The RA rings were suspended in isolated organ baths and tension was recorded isometrically. First, potassium chloride (KCl) and phenylephrine (PE) were added to organ baths to form precontraction. When the precontractions were stable, propofol (1, 10, and 100μM) was added cumulatively to the baths. The antagonistic effect of propofol on KCl (45mM), PE (1μM), 5-hydroxytryptamine (5-HT) (30μM), and calcium chloride (CaCl2) (10μM to 10mM) induced contractions in the vascular rings were investigated. Propofol-induced relaxations were alsotested in the presence of the K+ channel inhibitors tetraethylammonium (TEA, 1mM), glibenclamide (GLI, 10μM), 4-aminopyridine (4-AP, 1mM), and barium chloride (BaCl2, 30μM). Preincubation with propofol (1, 10, and 100μM) did not affect the basal tone but inhibited the contraction induced by KCl, PE, 5-HT, and CaCl2-induced contractions. Propofol-induced relaxation was not effected by 4-AP, GLI, and BaCl2. However, TEA inhibited propofol-induced relaxations significantly. The propofol induces relaxation in contracted RA and inhibits KCl, PE, 5-HT, andCaCl2-induced contractions. The results demonstrate that the mechanism of action of propofol-induced vasodilation in the RA may be related to large conductance Ca2+-activated K+ channel activation.

Vildagliptin, an Anti-diabetic Drug of the DPP-4 Inhibitor, Induces Vasodilation via Kv Channel and SERCA Pump Activation in Aortic Smooth Muscle.

This study investigated vildagliptin-induced vasodilation and its related mechanisms using phenylephrine induced precontracted rabbit aortic rings. Vildagliptin induced vasodilation in a concentration-dependent manner. Pretreatment with the large-conductance Ca2+-activated K+ channel blocker paxilline, ATP-sensitive K+ channel blocker glibenclamide, and inwardly rectifying K+ channel blocker Ba2+ did not affect the vasodilatory effects of vildagliptin. However, application of the voltage-dependent K+ (Kv) channel inhibitor 4-aminopyridine significantly reduced the vasodilatory effects of vildagliptin. In addition, application of either of two sarcoplasmic/endoplasmic reticulum Ca2+-ATPase (SERCA) inhibitors, thapsigargin or cyclopiazonic acid, effectively inhibited the vasodilatory effects of vildagliptin. These vasodilatory effects were not affected by pretreatment with adenylyl cyclase, protein kinase A (PKA), guanylyl cyclase, or protein kinase G (PKG) inhibitors, or by removal of the endothelium. From these results, we concluded that vildagliptin induced vasodilation via activation of Kv channels and the SERCA pump. However, other K+ channels, PKA/PKG-related signaling cascades associated with vascular dilation, and the endothelium were not involved in vildagliptin-induced vasodilation.

Abstract 16845: Functional Regulation of Native Coronary Kv1 Channels by Pyridine Nucleotides

Introduction: Recent studies indicate that vasodilation and enhanced blood flow to the heart following increases in myocardial O 2 demand are mediated by voltage-gated Kv1 channels in coronary smooth muscle cells (CVSM). Periods of high O 2 demand alter the intracellular pyridine nucleotide (PN) redox (e.g., elevated NADH:NAD + ), which, in heterologous systems, differentially modulates the gating properties of Kv1 channels by binding to intracellular Kvβ subunits. Hypothesis: Elevated levels of reduced PNs increase Kv1 channel activity in CVSM via the Kvβ complex. Methods: We performed patch clamp electrophysiology on CVSM freshly isolated from the left anterior descending coronary arteries (1 st and 2 nd order) of wild type and Kvβ2-null (Kvβ2 -/- ) mice. In the conventional whole cell configuration, we measured outward K + current density and the voltage-dependence of activation and inactivation (V 0.5, act, V 0.5,inact , respectively) in the absence and presence of extracellular lactate or pyruvate (10 mM), which alter intracellular PN levels. In inside-out membrane patches, we measured the open probability (nPo) of single K + -permeable channels that are sensitive to the Kv1 channel inhibitors 4-aminopyridine (4-AP; 1 mM) and psora-4 (500 nM), in the absence and presence of NADH (1 mM). Results: Treatment of wild type CVSM with lactate to elevate [NADH] I significantly increased whole cell Kv current density and shifted V 0.5, act to more negative membrane potentials (n=4, P<0.05). This response was effectively reversed upon increasing [NAD + ] i by treatment with pyruvate. Recordings performed in the inside-out configuration revealed K + currents that were sensitive to inhibition by psora-4 and 4-AP and had a unitary conductance of 70.2 ± 2.4 pS. Perfusion with a bath solution that contained 1 mM NADH lead to a significant increase (~2-fold) in the nPo of 4-AP-sensitive channels (n=25-30 cells, P<0.05). However, this effect was largely attenuated in membrane patches from Kvβ2 -/- CVSM. Conclusions: Native Kv1 channels in CVSM are functionally regulated by the intracellular NADH:NAD + ratio via their auxiliary Kvβ subunit complex.

The vasorelaxant effect of antidiabetic drug nateglinide via activation of voltage-dependent K+ channels in aortic smooth muscle.

We investigated the vasorelaxant effect of nateglinide and its related mechanisms using phenylephrine (Phe)-induced precontracted aortic rings. Arterial tone measurement was performed in aortic smooth muscle. The application of nateglinide induced vasorelaxation in a concentration-dependent manner. Pretreatment with the large-conductance Ca2+ -activated K+ (BKCa ) channel inhibitor paxilline, the inwardly rectifying K+ (Kir) channel inhibitor Ba2+ , and ATP-sensitive K+ (KATP ) channel inhibitor glibenclamide did not affect the vasorelaxant effect of nateglinide. However, pretreatment with the voltage-dependent K+ (Kv) channel inhibitor 4-aminopyridine (4-AP) effectively reduced the vasorelaxant effect of nateglinide. Pretreatment with the Ca2+ inhibitor nifedipine and the sarcoplasmic/endoplasmic reticulum Ca2+ -ATPase inhibitor thapsigargin did not change the vasorelaxant effect of nateglinide. Additionally, the vasorelaxant effect of nateglinide was not altered in the presence of an adenylyl cyclase, a protein kinase A, a guanylyl cyclase, or a protein kinase G inhibitor. The vasorelaxant effect of nateglinide was not affected by the elimination of the endothelium. In addition, pretreatment with a nitric oxide synthase inhibitor, L-NAME, and a small-conductance Ca2+ -activated K+ (SKCa ) channel inhibitor, apamin, did not change the vasorelaxant effect of nateglinide. Nateglinide induced vasorelaxation via the activation of the Kv channel independent of other K+ channels, Ca2+ channels, intracellular Ca2+ ([Ca2+ ]i ), and the endothelium.

Taurine relaxes human radial artery through potassium channel opening action.

The vascular actions and mechanisms of taurine were investigated in the isolated human radial artery (RA). RA rings were suspended in isolated organ baths and tension was recorded isometrically. First, a precontraction was achieved by adding potassium chloride (KCl, 45 mM) or serotonin (5-hydroxytryptamine, 5-HT, 30 µM) to organ baths. When the precontractions were stable, taurine (20, 40, 80 mM) was added cumulatively. Antagonistic effect of taurine on calcium chloride (10 µM to 10 mM)-induced contractions was investigated. Taurine-induced relaxations were also tested in the presence of the K+ channel inhibitors tetraethylammonium (1 mM), glibenclamide (10 µM) and 4-aminopyridine (1 mM). Taurine did not affect the basal tone but inhibited the contraction induced by 5-HT and KCl. Calcium chloride-induced contractions were significantly inhibited in the presence of taurine (20, 40, 80 mM) (p<0.05). The relaxation to taurine was inhibited by tetraethylammonium (p<0.05). However, glibenclamide and 4-aminopyridine did not affect taurine-induced relaxations. Present experiments show that taurine inhibits 5-HT and KCl-induced contractions in RA, and suggest that large conductance Ca2+-activated K+ channels may be involved in taurine-induced relaxation of RA.

Vasorelaxant effects of Shunaoxin pill are mediated by NO/cGMP pathway, HO/CO pathway and calcium channel blockade in isolated rat thoracic aorta

Ethnopharmacological relevanceShunaoxin pill (SNX), one of the famous classical recipes in traditional Chinese medicine, is developed from the “Decoction of Xionggui”. It has been used for treatment of cerebrovascular related diseases. It is well known that vasodilatation plays a very important role in cerebrovascular diseases. The effect of SNX on vasorelaxant activity has not yet been explored. Therefore, we aimed to investigate the vasorelaxant effects of SNX on isolated rat thoracic aorta so as to assess some of the possible mechanisms. We also investigate the gasotransmitter signaling pathway involved which has been rarely reported in isolated rat thoracic aorta before. Aim of the studyThe present study was performed to examine the vasodilative activity of SNX and its mechanisms in isolated rat thoracic aorta. Materials and methodsSNX was studied on isolated rat thoracic aorta in vitro, including endothelium-intact and endothelium-denuded aortic rings. In present study, specific inhibitors including soluble guanylate cyclase (sGC) inhibitor 1 H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one (ODQ), cyclooxygenase (COX) inhibitor indomethacin (INDO), NO synthase inhibitor NG-nitro-l-arginine methyl ester (L-NAME), heme oxygenase-1 (HO-1) inhibitor zinc-protoporphyrin (ZnPP), cystathionine γ-lyase (CSE) inhibitor DL-Propargylglycine (PAG), non-selective K+ channel inhibitor tetraethylammonium chloride (TEA), KV channel inhibitor 4-Aminopyridine (4-AP), and KATP channel inhibitor Glibenclamide (Gli) were used, they were added 20min before NE contraction and then added SNX to induce vasodilation. ResultsRemoval of endothelium or pretreatment of aortic rings (intact endothelium) with L-NAME, ODQ or ZnPP significantly blocked SNX-induced relaxation. Pretreatment with the non-selective K+ channel inhibitor TEA, KV channel inhibitor 4-AP or the KATP channel inhibitor Gli, none of them had influences on the SNX-induced response (p>0.05). Besides, SNX inhibited the contraction triggered by NE in endothelium-denuded rings in Ca2+-free medium. SNX also produced rightward parallel displacement of CaCl2 curves. ConclusionsThese results suggest that SNX can induce less endothelium-dependent and more endothelium-independent vascular relaxation. The NO/cGMP and HO/CO pathways, blockade of Ca2+ channels are inhibition of IP3R mediated Ca2+ mobilization from intracellular stores, are likely involved in this relaxation. Furthermore, the underlying mechanisms of combined compositions in SNX await further investigations.

Alpha-adrenoceptor antagonism by Crassostrea gigas oyster extract inhibits noradrenaline-induced vascular contraction in Wistar rats

ObjectiveCrassostrea gigas oyster extract has been reported to have antioxidant, antihypertensive and lipid-lowering properties that may be useful for treating cardiovascular diseases. This study aimed to evaluate the effect of C. gigas oyster extract on cardiovascular function in tissues from healthy rats. MethodsSingle-cell microelectrode and isolated thoracic aortic organ bath studies were performed on tissues from 8-week-old healthy Wistar rats, using varying concentrations of C. gigas oyster extract. To elucidate a mechanism of action for the oyster's vasoactive properties, concentration response curves were carried out in the presence of a calcium channel inhibitior (verapamil), a nitric oxide synthase inhibitor (NG-nitro-L-arginine methyl ester), a potassium channel inhibitor (4-aminopyridine), in addition to the α-adrenoceptor inhibitor prazosin. ResultsOyster solution at 7 500 mg/mL inhibited noradrenaline-induced contraction in isolated aortic rings. Cardiac electrophysiology results showed that neither concentration of oyster solution was able to significantly reduce action potential duration at all phases of repolarisation in left ventricular papillary muscles from healthy animals. ConclusionWhen administered to healthy vascular tissue, C. gigas oyster extract inhibits contraction induced by noradrenaline. This effect is likely to be mediated through α-adrenoceptor inhibition, and to a lesser extent, calcium modulating activity.

Characterization of the Relaxant Response to Taurine in Rat Corpus Cavernosum

The aim of this study was to evaluate the relaxant effect of taurine, one of the most commonly employed dietary supplements, in rat corpus cavernosum (CC), and to further investigate the contribution of possible underlying mechanisms. Strips of CC were suspended in an organ bath system for isometric tension studies. Taurine (10-80 mmol/l) produced a concentration-dependent relaxation response in rat CC. Endothelial removal did not cause a significant inhibition of the relaxation response to taurine. Incubation of endothelium-denuded CC strips with the nonselective potassium channel blocker tetraethylammonium (10 mmol/l), the ATP-sensitive potassium (K_ATP) channel blocker glibenclamide (10 μmol/l), the inward rectifier potassium (K_ir) channel inhibitor barium chloride (30 μmol/l), and the large conductance calcium-activated potassium channel inhibitor iberiotoxin (0.1 μmol/l) significantly inhibited the relaxant responses to taurine. However, taurine-induced relaxation was not inhibited by the voltage-dependent potassium channel inhibitor 4-aminopyridine (1 mmol/l). On the other hand, taurine (20 mmol/l, 30 min) inhibited both intracellular and extracellular calcium-dependent contraction in CC strips. These findings suggest that taurine induced relaxation of CC via an endothelium-independent pathway. The activation of K_ATP channels, K_ir channels and calcium channels is thought to play an important role in endothelium-independent relaxation of CC, but other direct effects on calcium dynamics may also contribute to its relaxant effect.

Ropivacaine-Induced Contraction Is Attenuated by Both Endothelial Nitric Oxide and Voltage-Dependent Potassium Channels in Isolated Rat Aortae

This study investigated endothelium-derived vasodilators and potassium channels involved in the modulation of ropivacaine-induced contraction. In endothelium-intact rat aortae, ropivacaine concentration-response curves were generated in the presence or absence of the following inhibitors: the nonspecific nitric oxide synthase (NOS) inhibitor N ω-nitro-L-arginine methyl ester (L-NAME), the neuronal NOS inhibitor N ω-propyl-L-arginine hydrochloride, the inducible NOS inhibitor 1400W dihydrochloride, the nitric oxide-sensitive guanylyl cyclase (GC) inhibitor ODQ, the NOS and GC inhibitor methylene blue, the phosphoinositide-3 kinase inhibitor wortmannin, the cytochrome p450 epoxygenase inhibitor fluconazole, the voltage-dependent potassium channel inhibitor 4-aminopyridine (4-AP), the calcium-activated potassium channel inhibitor tetraethylammonium (TEA), the inward-rectifying potassium channel inhibitor barium chloride, and the ATP-sensitive potassium channel inhibitor glibenclamide. The effect of ropivacaine on endothelial nitric oxide synthase (eNOS) phosphorylation in human umbilical vein endothelial cells was examined by western blotting. Ropivacaine-induced contraction was weaker in endothelium-intact aortae than in endothelium-denuded aortae. L-NAME, ODQ, and methylene blue enhanced ropivacaine-induced contraction, whereas wortmannin, N ω-propyl-L-arginine hydrochloride, 1400W dihydrochloride, and fluconazole had no effect. 4-AP and TEA enhanced ropivacaine-induced contraction; however, barium chloride and glibenclamide had no effect. eNOS phosphorylation was induced by ropivacaine. These results suggest that ropivacaine-induced contraction is attenuated primarily by both endothelial nitric oxide and voltage-dependent potassium channels.

DIFFERENT PATTERNS OF AORTIC STIFFNESS AND VASODILATION CAUSED BY β-BLOCKERS IN SPONTANEOUSLY HYPERTENSIVE RATS

ObjectivesThis study aims to investigate different patterns of aortic stiffness and vasodilation in spontaneously hypertensive rats treated with β-blockers, with or without vasodilatory properties.MethodsSpontaneously hypertensive rats (SHRs) were treated with...