Cigarette smoke induces pulmonary arterial dysfunction through an imbalance in the redox status of the soluble guanylyl cyclase.

Chronic obstructive pulmonary disease (COPD), whose main risk factor is cigarette smoking (CS), is one of the most common diseases globally. Some COPD patients also develop pulmonary hypertension (PH), a severe complication that leads to premature death. Evidence suggests reactive oxygen species (ROS) involvement in COPD and PH, especially regarding pulmonary artery smooth muscle cells (PASMC) dysfunction. However, the effects of CS-driven oxidative stress on the pulmonary vasculature are not completely understood. Herein we provide evidence on the effects of CS extract (CSE) exposure on PASMC regarding ROS production, antioxidant response and its consequences on vascular tone dysregulation. Our results indicate that CSE exposure promotes mitochondrial fission, mitochondrial membrane depolarization and increased mitochondrial superoxide levels. However, this superoxide increase did not parallel a counterbalancing antioxidant response in human pulmonary artery (PA) cells. Interestingly, the mitochondrial superoxide scavenger mitoTEMPO reduced mitochondrial fission and membrane potential depolarization caused by CSE. As we have previously shown, CSE reduces PA vasoconstriction and vasodilation. In this respect, mitoTEMPO prevented the impaired nitric oxide-mediated vasodilation, while vasoconstriction remained reduced. Finally, we observed a CSE-driven downregulation of the Cyb5R3 enzyme, which prevents soluble guanylyl cyclase oxidation in PASMC. This might explain the CSE-mediated decrease in PA vasodilation. These results provide evidence that there might be a connection between mitochondrial ROS and altered vasodilation responses in PH secondary to COPD, and strongly support the potential of antioxidant strategies specifically targeting mitochondria as a new therapy for these diseases.

Vasoactivity of magnesium sulfate in chicken ductus arteriosus.

Prenatal treatment with magnesium sulfate (MgSO4) has neuroprotective effects in very preterm infants but its use has been associated with an increased rate of patent ductus arteriosus (DA). MgSO4 is a vasodilator and thus may exert a direct relaxant effect in the DA. We aimed to investigate the vasoactive effects of MgSO4 in the DA using the chicken embryo as experimental model. DA rings from 15-d (E15), 17-d (E17) and 19-d (E19) chicken embryos (total incubation: 21-d) were mounted in a wire myograph for isometric tension recordings. Exposure of DA rings to 21% O2 induced a tonic contraction which was relaxed by MgSO4 (2.4 - 7.2 mmol L-1) in a concentration-dependent manner (mean maximal relaxation E19: 51.4%, SE 6.3; EC50: 3.5 mmol L-1, SE 0.7). The relaxation evoked by MgSO4 was not significantly different between E15, E17 and E19 DA and was not affected by removal of the endothelium or by the presence of the nitric oxide synthase inhibitor L-NAME, the soluble guanylate cyclase inhibitor ODQ, or the cyclooxygenase inhibitor indomethacin. In contrast, when the DA rings were incubated in Ca2+-free solution, or in the presence of inhibitors of L-type Ca2+ channels (nifedipine), or large-conductance Ca2+-activated K+ (BKCa) channels (iberiotoxin), MgSO4-induced relaxation was impaired. Preincubation of the DA rings with MgSO4 concentrations ranging from 0 to 6.0 mmol L-1 did not significantly affect O2-induced contraction that was only impaired by a concentration of 7.2 mmol L-1. In conclusion, MgSO4 induced endothelium-independent relaxation of chicken DA and this relaxation appeared to be mediated through stimulation of BKCa channels and blockade of transmembrane flux of extracellular Ca2+. However, O2-induced DA contraction was only impaired by suprapharmacological concentrations of MgSO4 (> 6.0 mmol L-1). Therefore, our data suggest that the higher incidence of patent DA in preterm infants exposed to MgSO4 is unlikely to be due to a direct pharmacological effect of the drug on the DA.

Quercetin and its metabolites inhibit the membrane NADPH oxidase activity in vascular smooth muscle cells from normotensive and spontaneously hypertensive rats.

Quercetin, the most abundant dietary flavonol, exerts antioxidant effects reducing vascular superoxide (O2(-)) and improving endothelial function in animal models of cardiovascular disease. Herein we evaluated the effects of quercetin, and its plasma metabolites, on the nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase activity, the main source of O2(-) in the vessel wall, in vascular smooth muscle cells (VSMCs) from spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY). Quercetin and its metabolites isorhamnetin and kaempferol inhibited the NADPH-stimulated lucigenin-chemiluminescence signal in VSMCs from both strains. The inhibitory effect of quercetin-3-glucuronide increased after prolonged incubation and was inhibited in the presence of the ß-glucuronidase inhibitor saccharolactone. These effects were unrelated to their O2(-) scavenging properties, since they induced only a small inhibition of the rate of pyrogallol autoxidation at high concentrations. All bioflavonoids tested acted as non-competitive inhibitors with respect to NADPH. In conclusion, quercetin and its metabolites inhibit the NADPH oxidase activity in VSMCs reducing O2(-) generation more efficiently than their effect as O2(-) scavengers. The effect of quercetin-3-glucuronide was due to deconjugation and release of free quercetin. The effect is similar in VSMCs from normotensive and hypertensive animals.

Prenatal exposure to hyperoxia modifies the thromboxane prostanoid receptor-mediated response to H2O2 in the ductus arteriosus of the chicken embryo.

O2 tension plays a critical role in the control of prenatal patency and postnatal closure of the ductus arteriosus (DA). We hypothesized that exposure of chicken embryos to hyperoxia alters the morphology and function of DA. Hyperoxia was induced by incubating fertilized eggs at 60% O2 from day 15 to 19 of the 21-d incubation period. DA reactivity (assessed by wire myography), morphometry and mRNA expression of antioxidant enzymes were studied on day 19. Hyperoxic incubation neither affected embryonic growth nor induced signs of DA constriction or changed the mRNA expression of superoxide dismutase and catalase. The contractions induced by O2 (21%), KCl, 4-aminopyridine, phenylephrine, and endothelin-1 and the relaxations induced by acetylcholine (ACh), sodium nitroprusside, isoproterenol, and hydroxyfasudil were similar in DA from embryos incubated under normoxic or hyperoxic conditions. In contrast, hyperoxic incubation impaired the thromboxane prostanoid (TP) receptor-mediated contractions evoked by U46619, 15-E2t-Isoprostane and high concentrations (≥3 µM) of ACh. Exogenous hydrogen peroxide (H2O2) evoked endothelium-dependent contraction in the normoxic DA and endothelium-dependent relaxation in the hyperoxic group. The presence of the TP receptor antagonist SQ 29548 unmasked a relaxant response to H2O2 in the normoxic DA and the cyclooxygenase (COX) inhibitor indomethacin blocked H2O2-induced contraction (in the normoxic group) and relaxation (in the hyperoxic group). Altogether our functional data suggest that, in the chicken DA, exogenous H2O2 induces the release of endothelium-derived COX metabolite(s) with contractile and relaxant properties. Under normal conditions H2O2-induced contraction prevails and relaxation is unmasked after pharmacological or functional (i.e.hyperoxia) TP receptor impairment.

PPARß activation restores the high glucose-induced impairment of insulin signalling in endothelial cells.

BACKGROUND AND PURPOSE: PPARß enhances insulin sensitivity in adipocytes and skeletal muscle cells, but its effects on insulin signalling in endothelial cells are not known. We analysed the effects of the PPARß/δ (PPARß) agonists, GW0742 and L165041, on impaired insulin signalling induced by high glucose in HUVECs and aortic and mesenteric arteries from diabetic rats. EXPERIMENTAL APPROACH: Insulin-stimulated NO production, Akt-Ser(473) and eNOS-Ser(1177) phosphorylation, and reactive oxygen species (ROS) production were studied in HUVECs incubated in low- or high-glucose medium. Insulin-stimulated relaxations and protein phosphorylation in vessels from streptozotocin (STZ)-induced diabetic rats were also analysed. KEY RESULTS: HUVECs incubated in high-glucose medium showed a significant reduction in insulin-stimulated production of NO. High glucose also reduced insulin-induced Akt-Ser(473) and eNOS-Ser(1177) phosphorylation, increased IRS-1-Ser(636) and ERK1/2-Thr(183) -Tyr(185) phosphorylation and increased ROS production. The co-incubation with the PPARß agonists GW0742 or L165041 prevented all these effects induced by high glucose. In turn, the effects induced by the agonists were suppressed when HUVEC were also incubated with the PPARß antagonist GSK0660, the pyruvate dehydrogenase kinase (PDK)4 inhibitor dichloroacetate or after knockdown of both PPARß and PDK4 with siRNA. The ERK1/2 inhibitor PD98059, ROS scavenger catalase, inhibitor of complex II thenoyltrifluoroacetone or uncoupler of oxidative phosphorylation, carbonyl cyanide m-chlorophenylhydrazone, also prevented glucose-induced insulin resistance. In STZ diabetic rats, oral GW0742 also improved insulin signalling and the impaired NO-mediated vascular relaxation. CONCLUSION AND IMPLICATIONS: PPARß activation in vitro and in vivo restores the endothelial function, preserving the insulin-Akt-eNOS pathway impaired by high glucose, at least in part, through PDK4 activation.

Developmental changes in endothelium-dependent relaxation of the chicken ductus arteriosus.

We tested the hypothesis that endothelium-dependent relaxation in the chicken ductus arteriosus (DA) is developmentally regulated. Isolated DA rings from 15-, 19- and 21-day-old (externally pipped) chicken embryos relaxed to acetylcholine (ACh). This relaxation was unaffected by indomethacin but impaired by endothelium removal, by the NO synthase inhibitor L-NAME, and by the soluble guanylate cyclase inhibitor ODQ, suggesting the involvement of NO. This NO production was confirmed with the fluorescent probe DAF-2DA. The combination of apamin and charybdotoxin with L-NAME produced a further inhibition of ACh-induced relaxation, suggesting the participation of a putative EDHF. In the 21-day DA, the relaxations induced by ACh and sodium nitroprusside (SNP) were markedly reduced and scanning electron microscopy demonstrated an irregular endothelial lining with protrusion and detachment of endothelial cells. The relaxations induced by BAY 41-2272 and 8-Br cGMP were not affected by age. When compared with 5%, lower (0%) and higher (21, 95%) O(2) concentrations impaired ACh-induced relaxation. In summary, we found that ACh induces endothelium-dependent relaxation of the chicken DA and that NO and EDHF are involved in this response. During chicken DA closure, endothelial cells undergo morphologic and functional alterations that result in the lack of endothelium-dependent relaxation.

[Visceral leishmaniasis and bronchial asthma: influence of steroid therapy in the development of the macrophage activation syndrome and relative adrenal insufficiency]. / Leishmaniasis visceral y asma bronquial: influencia del tratamiento esteroideo en el desarrollo del síndrome de activación macrofágica e insuficiencia suprarrenal relativa.

The risk of suffering opportunistics infections in the immunoincompetent patient is a fact perfectly established. An uncommon situation constitutes the bronchopaties, pathologies with a high prevalence among the general population that they require habitually, among other, steroid treatment. The immunosupression confers to the clinical evolution of the infections, as a consequence of the inadequate response to the physical stress, due to the inhibition of the hypothalamus-hypophysis axis being able to in particularly serious cases, to develop the denominated macrophage activation syndrome, a serious and uncommon syndrome that darkens the clinical prognosis in these patients. In presence of a feverish syndrome of uncertain origin in a patient in immunosuppressor treatment, although it is to low dose, it is necessary to carry out a exhaustive differential diagnosis, should consider, among them, the infection for Leishmania, a parasitosis whose incidence is increasing notably in the last years in the immunosuppressed population. We present the clinical case of a 63 year-old patient, immunoincompetent as a consequence of secondary chronic steroid therapy to asthmatic bronchopaty that experiences an uncommon form of visceral leishmaniasis in our area, consistent in multiorganic failure in the context of the development of a macrophage activation syndrome.

Propafenone modulates potassium channel activities of vascular smooth muscle from rat portal veins.

We have studied the effects of the class Ic antiarrhythmic propafenone on K+ currents in freshly isolated smooth muscle cells from rat portal veins and on the spontaneous contractions in whole tissues. Under Ca2+-free conditions, when cells were clamped at -80 mV (whole-cell configuration) depolarizing steps from -80 to +50 mV induced a family of K+ currents (I(Ktotal)) that mainly comprised the delayed rectifier current [I(K(V))], whereas when held at -10 mV only small-amplitude, noninactivating, currents (I(NI)) were recorded. Propafenone (10 microM) markedly inhibited I(Ktotal), but at potentials positive to +30 mV it also induced a noisy outwardly rectifying current [I(BK(Ca))] that was abolished by iberiotoxin (0.1 microM). Inhibition of I(Ktotal) by propafenone was concentration-dependent (EC50 = 0.059 +/- 0.009 microM). Propafenone also inhibited the transient outward current [I(K(A))] and ATP-sensitive potassium current [I(K(ATP))] induced by levcromakalim (10 microM). Inhibition of I(K(V)), I(K(A)), and I(K(ATP)) by propafenone was voltage-independent. In Ca(2+)-containing conditions propafenone inhibited I(K(V)) and I(BK(Ca)) and immediately abolished spontaneous outward transient K+ currents. In whole veins, propafenone behaved as the K(V) inhibitor 4-aminopyridine, increasing the amplitude and duration of spontaneous contractions. Propafenone also inhibited the inhibitory effects of the K(ATP) channel opener levcromakalim on spontaneous contractions. These results indicate that in vascular smooth muscle cells, propafenone inhibits K(V), K(A), BK(Ca), and K(ATP) channels. These actions correlated with its effects on mechanical activity in whole portal veins.

Pulmonary artery vasoconstriction but not [Ca2+]i signal stimulated by thromboxane A2 is partially resistant to NO.

To characterize the thromboxane A2 (TXA2) -induced resistance to the vasodilator effects of the nitric oxide (NO)/cGMP pathway in pulmonary arteries, we have studied the effects of the NO donor sodium nitroprusside on intracellular calcium concentration ([Ca2+]i) and contractile force recorded simultaneously in isolated piglet pulmonary arteries loaded with fura-2 and contracted with norepinephrine or the TXA2 mimetic U46619 and by activation of protein kinase C (PKC) with phorbol 12-myristate 13-acetate. In the TXA2 mimetic- and phorbol 12-myristate 13-acetate plus norepinephrine-stimulated arteries, nitroprusside exhibited lower vasodilator efficacy (and lower potency in the TXA2 mimetic-stimulated arteries) but similar reductions in [Ca2+]i compared with arteries activated by norepinephrine. The nonselective serine/threonine kinase inhibitor staurosporine, but not the selective inhibitor of PKC bisindolylmaleimide, potentiated the relaxation of nitroprusside in the TXA2 mimetic-stimulated arteries. In conclusion, the resistance to NO/cGMP-induced vasodilation in arteries stimulated by TXA2 and PKC involves a reduced ability of the Ca2+-independent mechanisms for smooth muscle vasodilation. The resistance to NO in arteries stimulated by TXA2 is sensitive to staurosporine but not to bisindolylmaleimide, suggesting the involvement of an activation of a serine/threonine kinase distinct from PKC.

Nitric oxide- and nitric oxide donors-induced relaxation and its modulation by oxidative stress in piglet pulmonary arteries.

Inhaled nitric oxide (iNO) is widely used in the treatment of pulmonary hypertension while inhaled NO donors have been suggested as an alternative therapy. The differential susceptibility to inactivation by oxidative stress and oxyhaemoglobin of NO and two NO donors, sodium nitroprusside (SNP) and S-nitroso-N-acetyl-penicillamine (SNAP) were analysed in isolated endothelium-denuded pulmonary arteries from 2-week-old piglets stimulated with U46619. NO, SNAP and SNP relaxed the arteries (pIC(30)=7.73+/-0.12, 7.26+/-0.17 and 6.43+/-0.13, respectively) but NO was not detected electrochemically in the bath after the addition of SNP and only at concentrations at which SNAP produced more than 50% relaxation. The sGC inhibitor ODQ (10(-6) M) or the sarcoplasmic Ca(2+)-ATPase thapsigargin (2x10(-6) M) markedly inhibited the relaxation induced by NO, SNAP and SNP. Addition of oxyhaemoglobin (3x10(-7) M) or diethyldithiocarbamate (1 mM) markedly inhibited NO- (pIC(30)=6.88+/-0.07 and 6.92+/-0.18, respectively), weakly inhibited SNAP- and had no effect on SNP-induced relaxation. Xanthine oxidase (5 mu ml(-1)) plus hypoxanthine (10(-4) M) markedly inhibited NO- (pIC(30)=6.96+/-0.12) but not SNAP- or SNP-induced relaxation. Superoxide dismutase (SOD), MnCl(2), diphenileneiodonium and exposing the luminal surface of the rings outwards (inversion) potentiated the relaxant responses of NO (pIC(30)=8.52+/-0.16, 8.23+/-0.11, 8.01+/-0.11 and 8.20+/-0.10, respectively). However, SOD did not modify the NO detected by the electrode and had no effect on SNAP- or SNP-induced relaxation. Therefore, the kinetics and local distribution of NO release of NO donors influence the susceptibility to the scavenging effects of oxyhaemoglobin and superoxide.

Mechanisms involved in SNP-induced relaxation and [Ca+]i reduction in piglet pulmonary and systemic arteries.

1. We have compared the mechanisms involved in sodium nitroprusside (SNP)-induced relaxation and [Ca2+]i reduction in isolated piglet pulmonary (PA) and mesenteric (MA) arteries. 2. SNP (10(-8) M-3x10(-5) M) evoked a concentration-dependent relaxation of PA and MA (pD2=6.66+/-0.06 and 6.74+/-0.14, respectively) stimulated by noradrenaline, which was markedly reduced by the guanylate cyclase inhibitor ODQ. In fura 2-incubated PA and MA, SNP produced a parallel reduction in contractile force and in [Ca2+]i, expressed as the ratio of emitted fluorescence at 340 and 380 nm (F340/F380). 3. The inhibition of the Na+/K+-ATPase after the incubation in a K+-free medium or the exposure to ouabain (10(-6) M) inhibited SNP-induced relaxation in MA but not in PA. SNP-induced relaxation was not attenuated by 80 mM KCl plus nifedipine (10(-6) M) but was inhibited by thapsigargin (2x10(-6) M; pD2=5.69+/-0.19 and 5.89+/-0.19 for PA and MA, respectively). 4. Pretreatment of PA with thapsigargin and MA with thapsigargin plus ouabain induced a stronger inhibition on the reduction in [Ca2+]i than on the relaxation induced by SNP, indicating the existence of Ca2+-independent mechanisms. 5. The activation of the Na+/K+-ATPase by the addition of KCl after the incubation in a K+-free medium similarly reduced [Ca2+]i in PA and MA, whereas it relaxed with much less efficacy PA than MA. 6. We conclude that SNP reduces [Ca2+]i and causes relaxation through the activation of SERCA in PA and SERCA and Na+/K+-ATPase in MA. However, Ca2+-independent mechanisms also contribute to SNP-induced effects.

Relaxant effects of carbon monoxide compared with nitric oxide in pulmonary and systemic vessels of newborn piglets.

Nitric oxide (NO) has been implicated in a number of diverse physiologic processes, including regulation of vascular tone. Carbon monoxide (CO) is another endogenously generated diatomic gas that may play an important physiologic role in vascular smooth muscle homeostasis. The purpose of this study was to compare the responses to exogenous NO and CO in isolated vessels (pulmonary arteries, pulmonary veins, and mesenteric arteries) from 12- to 24-h-old and 2-wk-old piglets. Vessels precontracted with the thromboxane A(2) mimetic U46619 (10(-7) M) relaxed in response to CO (2 x 10(-6) to 2 x 10(-4) M) and NO (2 x 10(-9) to 2 x 10(-7) M); these effects were not affected by endothelium removal but were completely abolished by the soluble guanylate cyclase inhibitor ODQ (10(-5) M). In pulmonary arteries, the maximal relaxation to NO increased with postnatal age from 33 +/- 4% of the precontraction value to 56 +/- 5%, in 12- to 24-h-old and 2-week-old piglets, respectively (p < 0.01), but the response to CO decreased from 25 +/- 3% to 12 +/- 1%, respectively (p < 0.01). The maximal response to CO was greater in pulmonary veins than in pulmonary or mesenteric arteries for both age groups (p < 0.01). Vasorelaxation induced by endogenous NO (stimulated by acetylcholine) was also greater in pulmonary veins when compared with pulmonary arteries and increased with postnatal age in both vessels. In contrast, no age-related differences were observed in the vasorelaxation induced by the cGMP analog 8-bromo cGMP in pulmonary arteries. When the response to NO was analyzed under three different extracellular O(2) concentrations (PO(2) 4.51 +/- 0.03, 19. 32 +/- 0.17, and 86 +/- 0.62, kPa), no significant differences were found. However, in the presence of superoxide dismutase (100 U/mL). the response to CO remained unchanged, and the response to NO improved in pulmonary arteries from 2-week-old but not from newborn piglets. In conclusion, both NO and CO relaxed neonatal vessels through soluble guanylate cyclase activation. However, when compared with NO, CO exhibited a poor vasorelaxant activity. Pulmonary vasorelaxation induced by NO increased with postnatal age, whereas that induced by CO decreased. Changes in extracellular oxygen concentration did not alter the pulmonary vascular response to NO. However, the presence of superoxide dismutase improved the response to NO, indicating that oxidant activity limits the vasorelaxant response to NO but not to CO.

Vasodilator effects of sodium nitroprusside, levcromakalim and their combination in isolated rat aorta.

1. The endothelial modulation of the relaxant responses to the nitric oxide (NO) donor sodium nitroprusside (SNP) and the KATP channel opener levcromakalim (LEM) and the interactions between these agents were analysed in isolated rat aorta. 2. LEM-induced relaxation was unchanged by endothelium removal or by the presence of L-NAME (10-4 M) or ODQ (10-6 M). In contrast, in KCl- (25 mM), but not in noradrenaline- (NA, 10-6 M) contracted arteries, SNP-induced relaxation was augmented by endothelium removal but not by L-NAME, indomethacin, glibenclamide nor charybdotoxin plus apamin. 3. The isobolographic analysis of the interactions between exogenously activated KATP channels and cyclic GMP using mixtures of SNP and LEM revealed that there were no interactions between both drugs at the proportions at which both drugs were active. However, the points for the SNP : LEM mixtures in proportions 10:1 and 1:10,000 (i.e. at concentrations at which LEM and SNP were inactive, respectively) fell significantly above the line of additivity indicating that there were negative interactions between both drugs at these selected proportions (about 5- and 2 fold inhibition, respectively). The former interaction was sensitive to glibenclamide, whereas the latter was insensitive ODQ. The magnitude of the 10:1 SNP:LEM interaction was smaller in endothelium-intact arteries and was absent in arteries stimulated by NA. 4. In conclusion, the relaxations induced by LEM and SNP were additive. However, the presence of endothelium and low concentrations of LEM inhibited SNP-induced relaxation. Both inhibitory effects were not additive and were only observed in KCl- and not in NA-contracted aortae.

Effects of nicorandil as compared to mixtures of sodium nitroprusside and levcromakalim in isolated rat aorta.

1. The contribution of the relaxant mechanisms of nicorandil (NIC) were analysed by comparing its effects with those of sodium nitroprusside (SNP), levcromakalim (LEM) and mixtures (1:10, 1:30 and 1:100) of SNP:LEM in isolated endothelium-denuded rat aorta. 2. In rings precontracted with KCl (25 mM), the relative inhibitory potency of the soluble guanylate cyclase inhibitor ODQ and the K(ATP) channel inhibitor glibenclamide (GLI) on SNP:LEM mixtures showed a good correlation with the relative proportion of SNP and LEM in the mixtures. Furthermore, the degree of the inhibition by ODQ and GLI of the effects of the 1:30 SNP:LEM mixture varied as a function of the relative potency of SNP and LEM in KCl-, noradrenaline- (NA) or NA plus nifedipine-treated arteries. 3. The inhibitory effects of ODQ, GLI and ODQ plus GLI on NIC-induced relaxation was similar to that for the 1:30 SNP:LEM mixture in NA plus nifedipine-contracted arteries, but the inhibition of GLI or ODQ plus GLI was smaller in KCl-contracted arteries. 4. In conclusion, the relative importance of activation of the cyclic GMP pathway and K(ATP) channel opening in mixtures of SNP and LEM could be predicted by the proportion of the drugs in the mixtures and by the relative potency of SNP vs LEM in different experimental conditions. Furthermore, the present results suggest that besides these two mechanisms, a third ODQ- and GLI-insensitive mechanism, possibly involving Ca2+ channel blockade, also participates in the relaxant effects of NIC in KCl-induced contractions.

Modulation of arterial Na+-K+-ATPase-induced [Ca2+]i reduction and relaxation by norepinephrine, ET-1, and PMA.

Na+-K+-ATPase plays a major role in regulating membrane potential and vascular tone. We analyzed the modulation by norepinephrine (NE), endothelin-1 (ET-1), and phorbol 12-myristate 13-acetate (PMA) of Na+-K+-ATPase-induced cytoplasmic free Ca2+ concentration ([Ca2+]i) reduction and relaxation in isolated endothelium-denuded piglet mesenteric arteries. KCl (0.2-8.8 mM)-induced [Ca2+]i reduction and relaxation in arteries incubated in K+-free solution were used as functional indicators of Na+-K+-ATPase activity. KCl-induced relaxations after exposure to K+-free solution were associated with a reduction in [Ca2+]i, as measured by fura 2 fluorescence. However, KCl reduced [Ca2+]i below resting values, whereas force was reduced to near resting values. NE, ET-1, and PMA inhibited the relaxant effects of KCl, and this effect was attenuated by the protein kinase C inhibitor staurosporine but not by the phospholipase A2 inhibitor quinacrine. However, ET-1 and PMA potentiated the [Ca2+]i-reducing effect of KCl. In conclusion, ET-1, PMA, and NE are functional inhibitors of Na+-K+-ATPase activity in endothelium-denuded piglet mesenteric arteries, even when the direct effect on the enzyme activity may be stimulatory rather than inhibitory. This can be explained because ET-1, PMA, and NE induce Ca2+ sensitization for smooth muscle contraction, and therefore relaxations do not parallel the reductions in [Ca2+]i after the activation of Na+-K+-ATPase.

Vasoconstrictor and vasodilator effects of disopyramide on isolated rat vascular smooth muscle.

We investigated the effects of disopyramide on the isometric contractions and intracellular Ca2+ concentrations ([Ca2+]i) measured by Fura-2 fluorescence in isolated rat aorta and portal veins. Disopyramide at concentrations > or = 10(-5) M increased the duration and complexity of the spontaneous contractions in rat portal veins. At > 10(-6) M, it induced a concentration-dependent contraction in the rat aorta. This effect was endothelium independent, associated with an increase in [Ca2+]i and abolished in aortic rings incubated in Ca2+-free solution or pretreated with 10(-7) M nifedipine, suggesting that disopyramide increased [Ca2+]i through the activation of L-type Ca2+ channels. In aortic rings precontracted by KCl (30 and 80 mM), 80 mM KCl in a low-concentration (26.2 mM) Na+ solution or 10(-5) M noradrenaline, disopyramide induced a concentration-dependent relaxation. The relaxant response in 80 mM KCl-precontracted arteries was associated with a parallel reduction in [Ca2+]i, an effect attributable to its Ca2+ channel blocking properties. In contrast, disopyramide had no effect on the concentration-response curves to noradrenaline in the presence of nifedipine. Disopyramide also inhibited in a concentration-dependent manner the relaxation induced by levcromakalim in aortic rings precontracted by 30 mM KCl because of its inhibitory action on K(ATP) channels, whereas it had no effect on the relaxant response to sodium nitroprusside. These effects, together with the negative inotropic effects of the drug, may account for the increase in mean arterial pressure observed in disopyramide-treated patients and the profound hypotension observed after overdosages of disopyramide.

Antagonism by class I antiarrhythmic drugs of levcromakalim-induced relaxation in isolated rat aorta.

We have analyzed the effects of several class I antiarrhythmic drugs (propafenone, quinidine, its enantiomer quinine, disopyramide, flecainide and mexiletine), tetraethylammonium (TEA) and glibenclamide on the vasodilator effects of the adenosine 5'-triphosphate-dependent K+ channels channel opener levcromakalim in isolated rat aorta precontracted by 30 mM KCl. TEA (>1 mM) and disopyramide (>/=10 microM), induced a sustained contraction in resting aortic rings. Propafenone (>/=3 microM), quinidine (>/=30 microM), disopyramide (>/=100 microM) and flecainide (>/=100 microM) but not the other drugs decreased the contraction induced by 30 mM KCl in a concentration-dependent manner. Propafenone (>/=1 microM), quinidine (>/=10 microM), quinine (>/=1 microM), disopyramide (>/=3 microM), flecainide (>/=100 microM), mexiletine (>/=3 microM), TEA (>/=0.3 mM) and glibenclamide (>/=0.1 microM) caused a concentration-dependent inhibition of the vasodilation induced by levcromakalim in rat aortic rings. The order of potency of the drugs, expressed as pD2 values, to inhibit the vasodilation induced by 0.3 microM levcromakalim was the following: glibenclamide (6.84) > quinine (6.14) > propafenone (5.27) > disopyramide (5.03) > quinidine (4.80) > mexiletine (4.68) > flecainide (3.37) > TEA (3. 20). With the exception of flecainide and mexiletine, the slopes of the Schild plots were similar to unity. Based on the mode of antagonism these drugs could be classified in four groups: 1) glibenclamide which only shifted the curves to the right, 2) quinidine and disopyramide that, at low concentrations, shifted the curve to the right but, at higher concentrations, it also reduced the maximal relaxant effect, 3) propafenone, quinine and TEA that shifted the curve rightwards and reduced the maximal relaxation at all concentrations and 4) flecainide and mexiletine whose Schild slopes were clearly different from unity. In conclusion, class I antiarrhythmic drugs inhibited levcromakalim-induced relaxation in isolated rat aorta. The concentrations at which these effects were observed were within the therapeutic range (except for flecainide) and similar to those reported to inhibit adenosine 5'-triphosphate-dependent K+ channel currents. Analysis of the concentration-response curves revealed that these drugs produced a noncompetitive antagonism of levcromakalim-induced relaxations.

Role of K+ channel opening and stimulation of cyclic GMP in the vasorelaxant effects of nicorandil in isolated piglet pulmonary and mesenteric arteries: relative efficacy and interactions between both pathways.

1. The effects of the K+ channel opener levcromakalim, the guanylate cyclase stimulant nitroprusside and the dual drug nicorandil (K+ channel opener and guanylate cyclase stimulant) were analysed in piglet isolated endothelium-denuded pulmonary (PA) and mesenteric (MA) arteries stimulated by noradrenaline (NA) or by the thromboxane A2 mimetic U46619. 2. Nicorandil, levcromakalim and verapamil were less potent in PA than in MA, the efficacy of levcromakalim was also reduced in PA. The effects of nicorandil and levcromakalim were similar in arteries pre-contracted by NA and U46619, whereas verapamil was more potent in arteries pre-contracted by NA. Nitroprusside was equipotent in MA pre-contracted by either NA or U46619 and in PA pre-contracted by NA whereas in PA pre-contracted by U46619, nitroprusside showed lower potency and efficacy. 3. The relaxant effects of levcromakalim and nitroprusside were inhibited by 10(-5) M glibenclamide and 10(-6) M ODQ, respectively. Nicorandil-induced relaxation was inhibited by ODQ in all experimental conditions, whereas glibenclamide had inhibitory effects in PA and MA pre-contracted by U46619, had no effect in PA pre-contracted by NA and in MA pre-contracted by NA it was only inhibitory in the presence of ODQ. 4. No apparent interactions were found between nitroprusside and levcromakalim as indicated by the lack of effects of pretreatment with one of them (producing 20-35% relaxation) on the potency of the relaxant response to the other. However, in PA pre-contracted by U46619, where nitroprusside or levcromakalim induced only partial relaxation, the combination of both mechanisms (either by combining nitroprusside plus levcromakalim or by nicorandil) was able to induce full vasodilatation. 5. In conclusion, K+ channel opening and guanylate cyclase stimulation are independent pathways that induce additive vasorelaxation in piglet PA and MA. The mechanism of action of nicorandil is dependent on the artery and on the nature of the agonist employed to precontract the artery. The relative efficacy of K+ channel opening vs guanylate cyclase stimulation may partially explain the preferential contribution of each mechanism to the relaxant effects of nicorandil.