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Biomedical subjects

Juan Tamargo

Publications and source records attributed to Juan Tamargo.

At least 19 recordsLinked to original sources
PubMed2007

Genetically engineered mice as a model for studying cardiac arrhythmias.

Sudden cardiac death due to ventricular tachyarrhythmias remains an unresolved problem, probably because the mechanisms responsible for the progression of cardiac disease to electrophysiological failure are poorly understood. Genetically engineered mice, the principal mammalian model for studying cardiac electrophysiology, have contributed to the understanding of the genetic, molecular and systemic mechanisms involved in the initiation and/or maintenance of cardiac arrhythmias leading to cardiac death, e.g. cardiac excitability, conduction velocity and refractoriness. Several murine models harbouring human gene mutations leading to electrical and structural cardiac disorders have been developed, including channelopathies (long QT syndrome), familial conduction disorders, cardiomyopathies and other inherited cardiac disorders. This article reviews the results of the main genetically modified mice addressing the genesis of cardiac arrhythmias and sudden cardiac death.

Animals↗
PubMed2006

The dietary flavonoid quercetin activates BKCa currents in coronary arteries via production of H2O2. Role in vasodilatation.

OBJECTIVE: Large conductance Ca(2+)-activated K(+) channels (BKCa) regulate coronary artery tone in vivo, play a key role in blood pressure regulation, and have been suggested as novel potential drug targets in hypertension. Quercetin exerts systemic and coronary vasodilator effects in vitro and reduces blood pressure in several rat models of hypertension, and its consumption is associated with a lower mortality rate from coronary heart disease in epidemiological studies. We hypothesized that quercetin might activate BKCa channel in isolated myocytes from rat coronary arteries and that this mechanism might be involved in its coronary artery relaxant effects. METHODS: Membrane currents were measured using the whole-cell configuration of the patch-clamp technique. Contractile tension was recorded in rat coronary artery rings mounted in a myograph. RESULTS: Quercetin (>0.1 muM) increased the outward currents in the whole range of test potentials, hyperpolarized cell membranes, and increased the frequency of spontaneous transient outward currents (STOCs) carried by BKCa channels. These effects were abolished by the selective BKCa blocker iberiotoxin and by catalase. Quercetin increased dichlorofluorescein fluorescence in coronary arteries in a polyethylenglycol-catalase-sensitive manner, indicating that it increased cytosolic H(2)O(2). The membrane-permeable analogue of H(2)O(2)t-butylhydroperoxide mimicked the effects of quercetin on outward currents. The vasodilator effect of quercetin in isolated rat coronary arteries was partially inhibited by iberiotoxin. CONCLUSION: Quercetin increased BKCa currents via production of intracellular H(2)O(2). This effect is involved, at least partly, in the coronary vasodilator effects of quercetin.

4-Aminopyridine↗
PubMed2006

Association of 14-3-3 proteins to beta1-adrenergic receptors modulates Kv11.1 K+ channel activity in recombinant systems.

We identify a new mechanism for the beta(1)-adrenergic receptor (beta(1)AR)-mediated regulation of human ether-a-go-go-related gene (HERG) potassium channel (Kv11.1). We find that the previously reported modulatory interaction between Kv11.1 channels and 14-3-3epsilon proteins is competed by wild type beta(1)AR by means of a novel interaction between this receptor and 14-3-3epsilon. The association between beta(1)AR and 14-3-3epsilon is increased by agonist stimulation in both transfected cells and heart tissue and requires cAMP-dependent protein kinase (PKA) activity. The beta(1)AR/14-3-3epsilon association is direct, since it can be recapitulated using purified 14-3-3epsilon and beta(1)AR fusion proteins and is abolished in cells expressing beta(1)AR phosphorylation-deficient mutants. Biochemical and electrophysiological studies of the effects of isoproterenol on Kv11.1 currents recorded using the whole-cell patch clamp demonstrated that beta(1)AR phosphorylation-deficient mutants do not recruit 14-3-3epsilon away from Kv11.1 and display a markedly altered agonist-mediated modulation of Kv11.1 currents compared with wild-type beta(1)AR, increasing instead of inhibiting current amplitudes. Interestingly, such differential modulation is not observed in the presence of 14-3-3 inhibitors. Our results suggest that the dynamic association of 14-3-3 proteins to both beta(1)AR and Kv11.1 channels is involved in the adrenergic modulation of this critical regulator of cardiac repolarization and refractoriness.

14-3-3 Proteins↗
PubMed2006

Nitric oxide blocks hKv1.5 channels by S-nitrosylation and by a cyclic GMP-dependent mechanism.

OBJECTIVE: This study was undertaken to analyze whether nitric oxide (NO) modulates the human potassium channel hKv1.5, which generates the ultrarapid delayed rectifier current (IKur) that determines the height and duration of atrial action potentials. METHODS: Currents were recorded using the whole-cell patch-clamp in Ltk- cells expressing hKv1.5 channels. RESULTS: The NO donors (+/-)-S-Nitroso-N-acetylpenicillamine (SNAP) and sodium nitroprusside, a NO solution, and l-Arginine inhibited hKv1.5 currents in a concentration-dependent manner. The NO concentration in the cell chamber was monitored using a sensor, and the IC50 for NO-induced hKv1.5 block was 340+/-70 nM. SNAP also inhibited the IKur recorded in mouse ventricular myocytes. The NO effects were partially mediated by the activation of the soluble guanylate cyclase (sGC)/cGMP/cGMP-dependent protein kinase (PKG) pathway. The biotin-switch assay demonstrated the presence of S-nitrosylated cysteines (Cys) on the hKv1.5 protein in SNAP-treated cells. Molecular modeling of hKv1.5 channel structure suggests that S-nitrosylation of Cys331 (segment 2, S2) and Cys346 (S2) would be stabilized by hydrogen bridge bonds with Ile262 (S1) and Arg342 (S2), respectively. CONCLUSIONS: NO inhibits the hKv1.5 current by a cGMP-dependent mechanism and by the S-nitrosylation of the hKv1.5 protein, an effect that contributes to shaping the human atrial action potentials.

Analysis of Variance↗
PubMed2006

Increased NADPH oxidase activity mediates spontaneous aortic tone in genetically hypertensive rats.

NADPH oxidase is critically involved in increased blood pressure, vascular hypertrophy, inflammation and endothelial dysfunction in experimental and clinical hypertension. We hypothesized that NADPH oxidase might also play a role in the development of spontaneous aortic tone in spontaneously hypertensive rats (SHR). Wistar Kyoto rats (WKY) were used as normotensive controls. Tone was recorded under isometric conditions. NADPH oxidase activity was measured by both lucigenin luminescence and dihydroethidium fluorescence. p47phox protein was localized by immunohistochemistry. SHR (but not WKY rat) aortae showed spontaneous tone in the absence of exogenous vasoconstrictors as evidenced by a stronger relaxant effect of Ca2+-free sodium nitroprusside solution. This tone was enhanced in endothelium-denuded arteries and was inhibited by superoxide dismutase, apocynin, diphenylene iodonium and quercetin. Aortic NADPH oxidase activity, measured by both lucigenin luminescence and dihydroethidium fluorescence, was increased in SHR compared with WKY rats. Immunohistochemical analysis revealed a strong increase in p47phox expression in the medial layer in SHR. Taken together, the present results indicate that enhanced NADPH oxidase activity and, hence, NADPH driven O2- production, is involved in the spontaneous aortic tone in SHR. This was associated with an increased expression of p47phox in the medial layer of the aorta.

Animals↗
PubMed2006

Relaxant effects of the soluble guanylate cyclase activator and NO sensitizer YC-1 in piglet pulmonary arteries.

BACKGROUND: The indazole derivative YC-1 has been characterized as a nitric oxide (NO)-independent and heme dependent soluble guanylate cyclase (sGC) activator, which also sensitizes sGC to NO. OBJECTIVE: To examine the effects of YC-1 on vascular relaxation in newborn and 2-week-old piglet pulmonary arteries. The effect of YC-1 on the relaxation induced by exogenous NO was also analyzed. METHODS: Isolated rings from third branch pulmonary arteries and fifth-seventh-generation intrapulmonary arterioles were mounted in organ chambers for isometric tension recording. Arteries were precontracted with the thromboxane A2 mimetic U46619. RESULTS: YC-1 induced relaxation was greater in 2-week-old pulmonary arteries and was abolished by the sGC inhibitor ODQ (10 microM). YC-1 induced relaxation was similar in conduit pulmonary arteries and arterioles. In the 2-week-old conduit pulmonary arteries, the response to YC-1 was significantly reduced when the endothelium was removed or after incubation with the NO synthase inhibitor L-NAME (0.1 mM). YC-1 augmented NO-induced relaxation in 2-week-old but not in neonatal conduit pulmonary arteries. CONCLUSIONS: Our results indicate that YC-1 induced pulmonary vascular relaxation in conduit and resistance pulmonary arteries and these effects increased with postnatal age. In the 2-week-old conduit pulmonary arteries and besides being a direct activator of sGC, YC-1 produced endothelium-dependent relaxation and synergized with exogenous NO.

Animals↗
PubMed2006

Serotonin inhibits voltage-gated K+ currents in pulmonary artery smooth muscle cells: role of 5-HT2A receptors, caveolin-1, and KV1.5 channel internalization.

Multiple lines of evidence indicate that serotonin (5-hydroxytryptamine [5-HT]) and voltage-gated K+ (KV) channels play a central role in the pathogenesis of pulmonary hypertension (PH). We hypothesized that 5-HT might modulate the activity of KV channels, therefore establishing a link between these pathogenetic factors in PH. Here, we studied the effects of 5-HT on KV channels present in rat pulmonary artery smooth muscle cells (PASMC) and on hKV1.5 channels stably expressed in Ltk- cells. 5-HT reduced native KV and hKV1.5 currents, depolarized cell membrane, and caused a contraction of isolated pulmonary arteries. The effects of 5-HT on KV currents and contraction were markedly prevented by the 5-HT2A receptor antagonist ketanserin. Incubation with inhibitors of phospholipase C (U73122), classic protein kinase Cs (Gö6976), or tyrosine kinases (genistein and tyrphostin 23), the cholesterol depletion agent beta-cyclodextrin or concanavalin A, an inhibitor of endocytotic processes, also prevented the effects of 5-HT. In homogenates from pulmonary arteries, 5-HT2A receptors and caveolin-1 coimmunoprecipitated with KV1.5 channels, and this was increased on stimulation with 5-HT. Moreover, KV1.5 channels were internalized when cells were stimulated with 5-HT, and this was prevented by concanavalin A. These findings indicate that activation of 5-HT2A receptors inhibits native KV and hKV1.5 currents via phospholipase C, protein kinase C, tyrosine kinase, and a caveolae pathway. KV channel inhibition accounts, at least partly, for 5-HT-induced pulmonary vasoconstriction and might play a role in PH.

Animals↗
PubMed2006

Proteomic study of plasma from moderate hypercholesterolemic patients.

Proteomics is a technology to detect and identify several proteins and their isoforms in a single sample. We used proteomics to analyze modifications in the protein map of plasma after simvastatin treatment of moderate hypercholesterolemic patients. Plasma from hypercholesterolemic patients (n = 9) was compared before and after 12 weeks of simvastatin treatment (40 mg/day). Patients with similar cardiovascular risk factors were used as controls (CR group). By using two-dimensional electrophoresis and mass spectrometry, we identified the different protein isoforms. The plasma expression of three fibrinogen gamma chain isoforms (FGG) was enhanced, whereas the expression of two isoforms of the fibrinogen beta chain (FGB) was reduced in the hypercholesterolemic patients compared with the CR group. The expression of apolipoprotein A-IV and three haptoglobin isoforms was higher in hypercholesterolemic patients. Simvastatin treatment modified the plasma expression of FGG chain isoform 1, FGB chain isoforms 1 and 2, vitamin D binding protein isoform 3, apo A-IV, and haptoglobin isoform 2. The modification of FGG chain isoform 1 and FGB chain isoforms 1 and 2 was positively correlated with total plasma cholesterol level. Proteomic analysis of plasma may help to know more in depth the molecular mechanism modified by simvastatin treatment.

Amino Acid Sequence↗
PubMed2006

Quercetin downregulates NADPH oxidase, increases eNOS activity and prevents endothelial dysfunction in spontaneously hypertensive rats.

BACKGROUND AND OBJECTIVE: Several studies have found that chronic treatment with the dietary flavonoid quercetin lowers blood pressure and restores endothelial dysfunction in hypertensive animal models. We hypothesized that increased endothelial nitric oxide synthase (eNOS) and/or decreased nicotinamide adenine dinucleotide phosphate (NADPH) oxidase protein expression and activity, and reduced reactive oxygen species might be involved in the improvement of endothelial function induced by quercetin in spontaneously hypertensive rats (SHR). DESIGN AND METHODS: Male SHR and Wistar-Kyoto (WKY) rats (5 weeks old) were treated with quercetin (10 mg/kg) or vehicle for 13 weeks. Changes in vascular expression of eNOS, caveolin-1 and p47 were analysed by Western blot, eNOS activity by conversion of [H]arginine to L-[H]citrulline, and NADPH oxidase activity by NADPH-enhanced chemoluminescence of lucigenin. RESULTS: In SHR, quercetin reduced the increase in blood pressure and heart rate and enhanced the endothelium-dependent aortic vasodilation induced by acetylcholine, but had no effect on the endothelium-independent response induced by nitroprusside. However, quercetin had no effect on endothelium-dependent vasoconstriction and aortic thromboxane B2 production. Compared to WKY, SHR showed upregulated eNOS and p47 protein expression, downregulated caveolin-1 expression, increased NADPH-induced superoxide production but, paradoxically, eNOS activity was reduced. Chronic quercetin treatment prevented all these changes in SHR. In WKY, quercetin had no effect on blood pressure, endothelial function or the expression or activity of the proteins analysed. CONCLUSIONS: Enhanced eNOS activity and decreased NADPH oxidase-mediated superoxide anion (O2) generation associated with reduced p47 expression appear to be essential mechanisms for the improvement of endothelial function and the antihypertensive effects of chronic quercetin.

Acetylcholine↗
PubMed2006

The safety of digoxin as a pharmacological treatment of atrial fibrillation.

Digoxin has traditionally been the drug of choice for ventricular rate control in patients with chronic atrial fibrillation (AF), with or without heart failure (HF) with systolic dysfunction. In patients with permanent AF, digoxin monotherapy is ineffective to control ventricular rate during exercise, but the combination of digoxin with a beta-blocker or a non-dihydropyridine calcium channel antagonist can control heart rate both at rest and during exercise. Only a few randomised, controlled studies have evaluated the adverse effects of digoxin in patients with AF in a systematic way and side effects requiring drug withdrawal have rarely been reported. When reported, the most frequent adverse effects were cardiac arrhythmias (ventricular arrhythmias, AV block of varying degrees and sinus pauses). This evidence suggested that, in contrast to other antiarrhythmic drugs, digoxin is a safe drug in patients with AF. However, this safety profile can be erroneous due to the short follow-up of the studies and patient selection. Because patients with HF have been excluded in most studies, the safety profile of digoxin in this population has not been directly addressed. Early recognition that an arrhythmia is related to digoxin intoxication as well as recognition of concomitant medications or medical conditions that may directly alter the pharmacokinetic profile of digoxin, or indirectly alter its cardiac effects by pharmacodynamic interactions remain essential for safe and effective use of digoxin in patients with AF.

Anti-Arrhythmia Agents↗
PubMed2005

Postnatal maturational shift from PKCzeta and voltage-gated K+ channels to RhoA/Rho kinase in pulmonary vasoconstriction.

OBJECTIVE: The neonate is at high risk of developing pulmonary hypertension, which may reflect a misbalance between vasodilator and vasoconstrictor agents. Thromboxane A(2) (TXA(2)) is involved in several forms pulmonary hypertension, but the signaling pathways mediating its pulmonary vasoconstrictor responses during postnatal maturation have not been analyzed. We therefore investigated the role of L-type Ca(2+) channels, protein kinase C (PKC) zeta, voltage-gated K(+) channels (K(V)), and RhoA/Rho kinase in TXA(2)-induced pulmonary vasoconstriction during postnatal maturation. METHODS: Changes in contractility and intracellular calcium were analyzed in 1 day (newborn) and 2-week-old piglets' pulmonary arteries (PA). K(V) currents were investigated in freshly isolated smooth muscle cells using the whole-cell configuration of the patch clamp technique. RESULTS: The contractile responses to the TXA(2) mimetic U46619 were similar at both ages but the L-type Ca(2+) channel blocker nifedipine and a PKCzeta pseudosubstrate inhibitor only attenuated the contraction in newborn PA. K(V) currents were similarly inhibited by U46619, although their density was dramatically reduced in 2-week-old as compared to newborn PA smooth muscle cells. This was consistent with a greater contraction to the K(V) inhibitor, 4-aminopyridine, and with a leftward shift in the increase in intracellular Ca(2+) by U46619 in newborn versus older animals. On the other hand, the Rho kinase inhibitor Y-27632 induced a stronger inhibitory effect on the contraction induced by U46619 in 2-week-old than in newborn PA and this was accompanied with minor effects on intracellular calcium levels. CONCLUSION: TXA(2)-induced pulmonary vasoconstriction involves PKCzeta-K(V)-L-type Ca(2+) channel and RhoA/Rho kinase signaling pathways, which are downregulated and upregulated, respectively, during postnatal maturation. The different contribution of these pathways could be of relevant importance for the vasodilator therapy choice in the treatment of pulmonary hypertension.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed2005

Angiotensin II, angiotensin II antagonists and spironolactone and their modulation of cardiac repolarization.

Angiotensin II and aldosterone produce pro-arrhythmic effects by several mechanisms, including the modulation of voltage-dependent K(+) channels involved in human cardiac repolarization. Drugs that inhibit the renin-angiotensin-aldosterone system exert anti-arrhythmic actions that are related to the blockade of the pro-arrhythmic actions of angiotensin II and aldosterone. These anti-arrhythmic actions include inhibition of electrical and structural cardiac remodeling, inhibition of neurohumoral activation, reduction of blood pressure and stabilization of electrolyte disturbances. In this article, several angiotensin II AT(1) receptor antagonists (candesartan, E3174, eprosartan, irbesartan and losartan) and aldosterone receptor antagonists (canrenoic acid and spironolactone) that directly modulate the activity of the voltage-dependent K(+) channels are reviewed; the effects of these antagonists might be useful in the prevention and treatment of cardiac arrhythmias.

Angiotensin II↗
PubMed2005

Spironolactone and its main metabolite canrenoic acid block hKv1.5, Kv4.3 and Kv7.1 + minK channels.

Both spironolactone (SP) and its main metabolite, canrenoic acid (CA), prolong cardiac action potential duration and decrease the Kv11.1 (HERG) current. We examined the effects of SP and CA on cardiac hKv1.5, Kv4.3 and Kv7.1+minK channels that generate the human I(Kur), I(to1) and I(Ks), which contribute to the control of human cardiac action potential duration.hKv1.5 currents were recorded in stably transfected mouse fibroblasts and Kv4.3 and Kv7.1 + minK in transiently transfected Chinese hamster ovary cells using the whole-cell patch clamp. SP (1 microM) and CA (1 nM) inhibited hKv1.5 currents by 23.2 +/- 3.2 and 18.9 +/- 2.7%, respectively, shifted the midpoint of the activation curve to more negative potentials and delayed the time course of tail deactivation.SP (1 microM) and CA (1 nM) inhibited the total charge crossing the membrane through Kv4.3 channels at +50 mV by 27.1 +/- 6.4 and 27.4 +/- 5.7%, respectively, and accelerated the time course of current decay. CA, but not SP, shifted the inactivation curve to more hyperpolarised potentials (V(h)-37.0 +/- 1.8 vs -40.8 +/- 1.6 mV, n = 10, P < 0.05).SP (10 microM) and CA (1 nM) also inhibited Kv7.1 + minK currents by 38.6 +/- 2.3 and 22.1 +/- 1.4%, respectively, without modifying the voltage dependence of channel activation. SP, but not CA, slowed the time course of tail current decay.CA (1 nM) inhibited the I(Kur) (29.2 +/- 5.5%) and the I(to1) (16.1 +/- 3.9%) recorded in mouse ventricular myocytes and the I(K) (21.8 +/- 6.9%) recorded in guinea-pig ventricular myocytes.A mathematical model of human atrial action potentials demonstrated that K(+) blocking effects of CA resulted in a lengthening of action potential duration, both in normal and atrial fibrillation simulated conditions. The results demonstrated that both SP and CA directly block hKv1.5, Kv4.3 and Kv7.1 + minK channels, CA being more potent for these effects. Since peak free plasma concentrations of CA ranged between 3 and 16 nM, these results indicated that blockade of these human cardiac K(+) channels can be observed after administration of therapeutic doses of SP. Blockade of these cardiac K(+) currents, together with the antagonism of the aldosterone proarrhythmic effects produced by SP, might be highly desirable for the treatment of supraventricular arrhythmias.

Animals↗
PubMed2005

New insights in the pharmacological therapy of arterial hypertension.

PURPOSE OF REVIEW: Despite the large number of antihypertensive drugs available, their usefulness is limited due to low efficacy, side effects, poor patient compliance and failure to reduce the cardiovascular risk to the level of the general population. These limitations have stimulated the research and development of new antihypertensive drugs, which we briefly review herein. RECENT FINDINGS: Novel antihypertensive drugs under development include new oral renin inhibitors, brain aminopeptidase A inhibitors, angiotensin-converting enzyme 2 modulators, short-acting L-type Ca channel blockers, new T-type Ca channel blockers, inhibitors of vascular NAD(P)H oxidase, angiotensin-converting enzyme crosslink breakers, Rho kinase inhibitors, renal Na/K ATPase inhibitors, potassium channel openers and drugs combining different mechanisms of action. SUMMARY: Essential hypertension is a multifactorial and multigenic disorder, which means that various mechanisms contribute to a greater or lesser extent to increasing blood pressure. Drugs combining several mechanisms of action or combinations of antihypertensive drugs with those targeting other risk factors may offer an alternative to reduce overall cardiovascular risk. As we improve our understanding of essential hypertension, it should be possible to develop safer and more effective antihypertensive drugs. The risk/benefit ratio of these new existing antihypertensive drugs will require long-term endpoint assessment studies.

Antihypertensive Agents↗