Elsevier

Vascular Pharmacology

Volume 47, Issues 2–3, August–September 2007, Pages 139-144
Vascular Pharmacology

Vasorelaxation induced by the new nitric oxide donor cis-[Ru(Cl)(bpy)2(NO)](PF6) is due to activation of KCa by a cGMP-dependent pathway

https://doi.org/10.1016/j.vph.2007.05.003Get rights and content

Abstract

We investigated the effects of selective K+ channel blockers and guanylyl cyclase inhibitor on the rat aorta relaxation induced by the new NO donor cis-[Ru(Cl)(bpy)2(NO)](PF6) (RUNOCL), following endothelium removal. NO release from RUNOCL was obtained by photo-induction using a visible light system λ > 380 nm. RUNOCL induced relaxation of phenylephrine contracted aortic rings under light with the maximum effect (ME) of 101.2 ± 3.7% and pD2: 6.62 ± 0.16 (n = 7), but not in the absence of light. Relaxation stimulated with RUNOCL was also studied on 60 mM of KCl-contracted arteries or after incubation with the non-selective K+ channel blocker (1 mM TEA) or the selective K+ channel blockers (3 μM glibenclamide (KATP), 1 mM 4-aminopyridine (KV, 4-AP), 1 μM apamin (SKCa-APA) or 0.1 μM iberiotoxin (BKCa IBTX). Relaxation induced by RUNOCL was lower in KCl-contracted aortic rings with ME of 68.6 ± 10.0% and pD2: 3.92 ± 0.60 (n = 4). As compared to Phe-contracted arteries the potency of RUNOCL in inducing rat aorta relaxation was reduced by K+ channel blockers as demonstrated by the pD2 values from 6.62 ± 0.16 (n = 7) (control) to (TEA: 5.32 ± 0.108, n = 5; IBTX: 5.63 ± 0.02 (n = 5), APA: 5.73 ± 0.13 (n = 5)). But the ME was reduced only by IBTX (60.7 ± 3.4%). 4-AP and glibenclamide had no effect on the relaxation induced by RUNOCL. The aortic tissue cGMP content increased with RUNOCL under light irradiation from 63.13 ± 0.45 fmol/μg to 70.56 ± 4.64 fmol/μg of protein (n = 4) and the inhibition of guanylyl cyclase with ODQ reduced the ME: 30.1 ± 1.6% and pD2: 6.35 ± 0.05 (n = 4). Our results suggest that the NO released by photo-induction from RUNOCL induces rat aorta relaxation by activation of KCa by a cGMP-dependent pathway.

Introduction

Nitric oxide (NO) plays an important role in the control of vascular tone, and it is a free radical gas, which is known as a multifunctional and ubiquitous biological messenger molecule. NO can bind to the heme site of soluble guanylyl cyclase (sGC) (Feelisch et al., 1988), activating the enzyme and catalyzing the conversion of GTP to cGMP (Noack and Feelisch, 1991) and inducing a downstream signaling cascade. This cascade includes activation of a kinase downstream from cGMP, protein kinase G and subsequent decrease of cytosolic calcium concentration, leading to vasodilation (McDonald and Murad, 1996, Murad, 1994).

Several NO donors have been used in clinical settings for decades (e.g., nitroglycerin and sodium nitroprusside). However, the growth of interest in the physiology of NO since the mid 1980s has led to the development of a variety of new NO donors that offer several advantages over conventional NO donors (Ignarro, 2002). The amount and duration of the NO released by respective NO donors determines their pharmacological properties.

Nitric oxide released from NO donors or cGMP have been shown to activate smooth-muscle K+ channels in cerebral arteries (Hempelmann et al., 2000, Hempelmann et al., 2001, Wang et al., 2000). Thus, a cGMP-mediated hyperpolarization due to the opening of K+ channels with subsequent deactivation of voltage-dependent Ca2+ channels and decreasing intracellular Ca2+ activity is one of the mechanism of NO-induced vasorelaxation (Lovren and Triggle, 1998, Sand et al., 2006, Wang et al., 2000).

When K+ channels open in the vascular smooth-muscle cell membrane, K+ efflux increases, causing membrane hyperpolarization, decreased Ca2+ entry (through voltage-operated Ca2+ channels) and vasodilatation (Bolotina et al., 1994). Several types of K+ channels have been identified in vascular smooth-muscle and endothelium. The most abundant includes the large conductance calcium dependent K+ channels and voltage-sensitive K+ channel (Kv). Also present are the intermediate and small-conductance calcium sensitive K+ channels (IKCa and SKCa), the ATP-sensitive K+ channel (KATP) and the inward-rectifying potassium channels (Kir) (Brayden, 1996, Vergara et al., 1998).

Recently, new metal complexes have been studied as NO donors, including nitrosyl ruthenium complexes (Bonaventura et al., 2004, Lunardi et al., 2006b, Wang et al., 2000).The ability of controlling the NO release to the biological medium could be done by the synthesis of an appropriated structure controlling chemical properties such as redox potential and photochemistry. The ruthenium complex used in this study release NO only under photoactivation. This study aimed to investigate the effect of NO released from the new NO donor cis-[Ru(Cl)(bpy)2(NO)](PF6) (RUNOCL) on the rat aorta relaxation and the mechanism involved in this relaxation and the effects of K+ channel blockers and guanylyl cyclase inhibitor (Scheme 1).

Section snippets

Animals

For vasodilation studies, male Wistar rats (200–250 g) were used. The rats were killed by decapitation and all the procedures are in compliance with the Ethical Animal Committee by the University of São Paulo, Brazil.

Measurements of cis-[Ru(Cl)(bpy)2(NO)](PF6) (RUNOCL)-induced vasodilation

The thoracic aorta was removed, cleaned of adherent connective tissues, and cut into rings 4 mm length. The endothelium was removed mechanically by gently rolling the lumen of the vessel on a thin wire. The aortic rings were placed between two stainless-steel stirrups and connected

Results

On denuded aortic rings pre-contracted with Phe (0.1 μM), RUNOCL (0.1–100 μM) caused a concentration-dependent developing relaxation with the ME:101.2 ± 3.7% and pD2: 6.62 ± 0.16, P<0.002 (n = 7) (Fig. 1), however the effect was evident only under photo-induction using a visible light system λ > 380 nm. The maximum aorta relaxation (Time-course) induced by RUNOCL was achieved in 1630 s. The synthesized NO donor also relaxed KCl (60 mM) pre-contracted tissue with the ME: 68.6 ± 10.0%, P < 0.01 and pD2: 3.92

Discussion

We reported for the first time that the new NO-donor RUNOCL induces vasorelaxation due to cGMP and Kca channel-activated pathway. Vascular relaxation to NO may occur due to guanylyl cyclase activation and also through a cGMP-independent activation of K+ channels directly on the vascular smooth-muscle cells (Bolotina et al., 1994). In agreement with these findings, we have shown that in response to NO donor the cytosolic calcium concentration decreased in the isolated vascular smooth-muscle

Acknowledgments

This work was supported by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq).

References (27)

  • C. Cauvin et al.

    Mechanisms of calcium antagonist-induced vasodilation

    Annu. Rev. Pharmacol. Toxicol.

    (1983)
  • M. Feelisch et al.

    Explanation of the discrepancy between the degree of organic nitrate decomposition, nitrite formation and guanylate cyclase stimulation

    Eur. Heart J.

    (1988)
  • R.G. Hempelmann et al.

    Effects of potassium channel inhibitors on the relaxation induced by the nitric oxide donor diethylamine nitric oxide in isolated human cerebral arteries

    J. Neurosurg.

    (2000)
  • Cited by (34)

    • Endothelium-independent vasodilator effects of nobiletin in rat aorta

      2019, Journal of Pharmacological Sciences
      Citation Excerpt :

      Quercetin is a flavonoid which has been reported to relax vascular smooth muscle by opening a voltage-gated K+ channel.12 It has been reported that the opening of K+ channels is the one of mechanisms involved in cGMP-mediated relaxation in vascular smooth muscle.13–15 In order to investigate the involvement of nobiletin in the opening of K+ channels, a range of K+ channel inhibitors were used in endothelium-denuded aorta.

    • Hypotensive effect and vascular relaxation in different arteries induced by the nitric oxide donor RuBPY

      2017, Nitric Oxide - Biology and Chemistry
      Citation Excerpt :

      Moreover, they present thermal stability and stability in physiological pH [4]. Ruthenium NO donor compounds have emerged as an important class of drugs that induces vascular relaxation [5–9], and reduces the blood pressure in hypertensive animals [10,11]. cis-[Ru(bpy)2(py)(NO2)](PF6) (RuBPY) is a nitrite-ruthenium, since it has a NO2 in its molecule.

    • The versatile ruthenium(II/III) tetraazamacrocycle complexes and their nitrosyl derivatives

      2016, Coordination Chemistry Reviews
      Citation Excerpt :

      Another factor for vasodilation in the smooth muscle cells is cytosolic calcium concentration decrease by calcium entry inhibition [214]. Studies indicate that the NO/cGMP pathway can decrease intracellular calcium concentration and reduce the contractile sensibility in the smooth muscle relaxation [215–218]. The ruthenium nitrosyls trans-[Ru(NO)Cl([15]aneN4)]2+, [Ru(NO)(NH·NHq)(terpy)](PF6)3 (Fig. 16), and cis-[Ru(NO)Cl(bpy)2](PF6)2 decrease calcium concentration in the vascular media [219], which means that they could contribute for vasorelaxation by two ways: by K+ channel activation in the cGMP-dependent and -independent pathways, which decreases cytosolic Ca2+ concentration [51].

    • Design, reactivity, and biological activity of ruthenium nitrosyl complexes

      2015, Advances in Inorganic Chemistry
      Citation Excerpt :

      The relaxation induced by ruthenium compounds involves activation of cyclic guanosine 3′,5′-monophosphate (cGMP), which could mediate several biological mechanisms. As described in our work (27,32,39,42–51) one of these mechanisms involves activation of a calcium-sensitive potassium channel through the cGMP-dependent protein kinase. Another common process is induction of cell membrane hyperpolarization.

    • The ruthenium NO donor, [Ru(bpy)<inf>2</inf>(NO)SO<inf>3</inf>](PF <inf>6</inf>), inhibits inflammatory pain: Involvement of TRPV1 and cGMP/PKG/ATP-sensitive potassium channel signaling pathway

      2013, Pharmacology Biochemistry and Behavior
      Citation Excerpt :

      Furthermore, it was observed that complex I induced analgesia by activating the cGMP/PKG/ATP-sensitive potassium channel pathway (present data) similarly to morphine and diclofenac (Cunha et al., 2010, 2012; Tonussi and Ferreira, 1994). In agreement with this mechanism, other ruthenium NO donors induce vasorelaxant effects in a soluble guanylate cyclase- and potassium channels-dependent manner (Lunardi et al., 2007; Pereira et al., 2011). Furthermore, we speculate that the activation of the cGMP/PKG/ATP-sensitive potassium channel pathway by complex I is a neuronal events as for morphine, which is also consistent with the inhibition of the first phase of formalin test described as a neuronal phase (Dubuisson and Dennis, 1977; present data).

    View all citing articles on Scopus
    View full text