Biomedical subjects

Eduardo Marbán

Publications and source records attributed to Eduardo Marbán.

At least 19 recordsLinked to original sources

PubMed2006

Cellular and molecular determinants of altered Ca2+ handling in the failing rabbit heart: primary defects in SR Ca2+ uptake and release mechanisms.

Myocytes from the failing myocardium exhibit depressed and prolonged intracellular Ca(2+) concentration ([Ca(2+)](i)) transients that are, in part, responsible for contractile dysfunction and unstable repolarization. To better understand the molecular basis of the aberrant Ca(2+) handling in heart failure (HF), we studied the rabbit pacing tachycardia HF model. Induction of HF was associated with action potential (AP) duration prolongation that was especially pronounced at low stimulation frequencies. L-type calcium channel current (I(Ca,L)) density (-0.964 +/- 0.172 vs. -0.745 +/- 0.128 pA/pF at +10 mV) and Na(+)/Ca(2+) exchanger (NCX) currents (2.1 +/- 0.8 vs. 2.3 +/- 0.8 pA/pF at +30 mV) were not different in myocytes from control and failing hearts. The amplitude of peak [Ca(2+)](i) was depressed (at +10 mV, 0.72 +/- 0.07 and 0.56 +/- 0.04 microM in normal and failing hearts, respectively; P < 0.05), with slowed rates of decay and reduced Ca(2+) spark amplitudes (P < 0.0001) in myocytes isolated from failing vs. control hearts. Inhibition of sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA)2a revealed a greater reliance on NCX to remove cytosolic Ca(2+) in myocytes isolated from failing vs. control hearts (P < 0.05). mRNA levels of the alpha(1C)-subunit, ryanodine receptor (RyR), and NCX were unchanged from controls, while SERCA2a and phospholamban (PLB) were significantly downregulated in failing vs. control hearts (P < 0.05). alpha(1C) protein levels were unchanged, RyR, SERCA2a, and PLB were significantly downregulated (P < 0.05), while NCX protein was significantly upregulated (P < 0.05). These results support a prominent role for the sarcoplasmic reticulum (SR) in the pathogenesis of HF, in which abnormal SR Ca(2+) uptake and release synergistically contribute to the depressed [Ca(2+)](i) and the altered AP profile phenotype.

Abdomen↗

PubMed2006

Gene transfer of a synthetic pacemaker channel into the heart: a novel strategy for biological pacing.

BACKGROUND: One key element of natural pacemakers is the pacemaker current encoded by the hyperpolarization-activated nucleotide-gated channel (HCN) gene family. Although HCN gene transfer has been used to engineer biological pacemakers, this strategy may be confounded by unpredictable consequences of heteromultimerization with endogenous HCN family members and limited flexibility with regard to frequency tuning of the engineered pacemaker. METHODS AND RESULTS: To circumvent these limitations, we converted a depolarization-activated potassium-selective channel, Kv1.4, into a hyperpolarization-activated nonselective channel by site-directed mutagenesis (R447N, L448A, and R453I in S4 and G528S in the pore). Gene transfer into ventricular myocardium demonstrated the ability of this construct to induce pacemaker activity with spontaneous action potential oscillations in adult ventricular myocytes and idioventricular rhythms by in vivo electrocardiography. CONCLUSIONS: Given the sparse expression of Kv1 family channels in the human ventricle, gene transfer of a synthetic pacemaker channel based on the Kv1 family has novel therapeutic potential as a biological alternative to electronic pacemakers.

Animals↗

PubMed2006

Proteomic analysis of pharmacological preconditioning: novel protein targets converge to mitochondrial metabolism pathways.

Ischemic preconditioning is characterized by resistance to ischemia reperfusion injury in response to previous short ischemic episodes, a protective effect that can be mimicked pharmacologically. The underlying mechanism of protection remains controversial and requires greater understanding before it can be fully exploited therapeutically. To investigate the overall effect of preconditioning on the myocardial proteome, isolated rabbit ventricular myocytes were treated with drugs known to induce preconditioning, adenosine or diazoxide (each at 100 micromol/L for 60 minutes). Their protein profiles were then compared with vehicle-treated controls (n=4 animals per treatment) using a multitiered 2D gel electrophoresis approach. Of 28 significantly altered protein spots, 19 nonredundant proteins were identified (5 spots remained unidentified). The majority of these proteins are involved in mitochondrial energetics, including subunits of tricarboxylic acid cycle enzymes and oxidative phosphorylation complexes. These changes were not indiscriminate, with only a small number of enzymes or complex subunits altered, indicating a very specific and targeted affect of these 2 preconditioning mimetics. Among the changes were shifts in the extent of posttranslational modification of 4 proteins. One of these, the adenosine-induced phosphorylation of the ATP synthase beta subunit, was fully characterized with the identification of 5 novel phosphorylation sites. This proteomics approach provides an overall assessment of the cellular response to pharmacological treatment with adenosine and diazoxide and identifies a distinct subset of enzymes and protein complex subunit that may underlie the preconditioned phenotype.

Adenosine↗

PubMed2006

A computational model integrating electrophysiology, contraction, and mitochondrial bioenergetics in the ventricular myocyte.

An intricate network of reactions is involved in matching energy supply with demand in the heart. This complexity arises because energy production both modulates and is modulated by the electrophysiological and contractile activity of the cardiac myocyte. Here, we present an integrated mathematical model of the cardiac cell that links excitation-contraction coupling with mitochondrial energy generation. The dynamics of the model are described by a system of 50 ordinary differential equations. The formulation explicitly incorporates cytoplasmic ATP-consuming processes associated with force generation and ion transport, as well as the creatine kinase reaction. Changes in the electrical and contractile activity of the myocyte are coupled to mitochondrial energetics through the ATP, Ca2+, and Na+ concentrations in the myoplasmic and mitochondrial matrix compartments. The pseudo steady-state relationship between force and oxygen consumption at various stimulus frequencies and external Ca2+ concentrations is reproduced in both model simulations and direct experiments in cardiac trabeculae under normoxic conditions, recapitulating the linearity between cardiac work and respiration in the heart. Importantly, the model can also reproduce the rapid time-dependent changes in mitochondrial NADH and Ca2+ in response to abrupt changes in workload. The steady-state and dynamic responses of the model were conferred by ADP-dependent stimulation of mitochondrial oxidative phosphorylation and Ca2+ -dependent regulation of Krebs cycle dehydrogenases, illustrating how the model can be used as a tool for investigating mechanisms underlying metabolic control in the heart.

Action Potentials↗

PubMed2006

A common genetic variant in the NOS1 regulator NOS1AP modulates cardiac repolarization.

Extremes of the electrocardiographic QT interval, a measure of cardiac repolarization, are associated with increased cardiovascular mortality. We identified a common genetic variant influencing this quantitative trait through a genome-wide association study on 200 subjects at the extremes of a population-based QT interval distribution of 3,966 subjects from the KORA cohort in Germany, with follow-up screening of selected markers in the remainder of the cohort. We validated statistically significant findings in two independent samples of 2,646 subjects from Germany and 1,805 subjects from the US Framingham Heart Study. This genome-wide study identified NOS1AP (CAPON), a regulator of neuronal nitric oxide synthase, as a new target that modulates cardiac repolarization. Approximately 60% of subjects of European ancestry carry at least one minor allele of the NOS1AP genetic variant, which explains up to 1.5% of QT interval variation.

Adaptor Proteins, Signal Transducing↗

PubMed2006

Proarrhythmic potential of mesenchymal stem cell transplantation revealed in an in vitro coculture model.

BACKGROUND: Mesenchymal stem cells (MSCs) are bone marrow stromal cells that are in phase 1 clinical studies of cellular cardiomyoplasty. However, the electrophysiological effects of MSC transplantation have not been studied. Although improvement of ventricular function would represent a positive outcome of MSC transplantation, focal application of stem cells has the potential downside of creating inhomogeneities that may predispose the heart to reentrant arrhythmias. In the present study we use an MSC and neonatal rat ventricular myocyte (NRVM) coculture system to investigate potential proarrhythmic consequences of MSC transplantation into the heart. METHODS AND RESULTS: Human MSCs were cocultured with NRVMs in ratios of 1:99, 1:9, and 1:4 and optically mapped. We found that conduction velocity was decreased in cocultures compared with controls, but action potential duration (APD80) was not affected. Reentrant arrhythmias were induced in 86% of cocultures containing 10% and 20% MSCs (n=36) but not in controls (n=7) or cocultures containing only 1% MSCs (n=4). Immunostaining, Western blot, and dye transfer revealed the presence of functional gap junctions involving MSCs. CONCLUSIONS: Our results suggest that mixtures of MSCs and NRVMs can produce an arrhythmogenic substrate. The mechanism of reentry is probably increased tissue heterogeneity resulting from electric coupling of inexcitable MSCs with myocytes.

Animals↗

PubMed2006

Murine strain differences in contractile function are temperature- and frequency-dependent.

Despite the widespread use of mice in the investigation of cardiac function, little is known as to what extent cardiac contractile function varies between different murine strains. We have investigated basic contractile function in isolated multicellular right ventricular trabeculae from three commonly used mouse strains (C57BL/6, SV129, and FVBN). Suitable trabeculae (<100 microm thick, >1 mm long) occurred rather frequently in FVBN and SV129 mice (on average about 2 per heart), but only sporadically in C57BL/6 mice (on average only 1 per 3-4 mice). However, using similar sized preparations under experimental conditions closely mimicking those in vivo (37 degrees C and frequencies between 8 and 12 Hz), contractile function was virtually identical. In addition, the magnitude of response to beta-adrenergic stimulation was also indistinguishable between the strains. However, at subphysiological frequency, FVBN mice consistently displayed more developed force compared to C57/BL6 and SV129 mice. Furthermore, contractile performance at a subphysiological temperature and frequency, where studies on isolated myocardium often are performed, was also strain-dependent. We conclude that basic contractile function under near physiological conditions is preserved throughout various strains, but subphysiological conditions can have a profound effect on contractile performance. Hence, choice of strain can have important implications for cardiac contractile function under nonphysiological conditions.

Animals↗

PubMed2005

Xanthine oxidase inhibitors improve energetics and function after infarction in failing mouse hearts.

After myocardial infarction, ventricular geometry and function, as well as energy metabolism, change markedly. In nonischemic heart failure, inhibition of xanthine oxidase (XO) improves mechanoenergetic coupling by improving contractile performance relative to a reduced energetic demand. However, the metabolic and contractile effects of XO inhibitors (XOIs) have not been characterized in failing hearts after infarction. After undergoing permanent coronary ligation, mice received a XOI (allopurinol or oxypurinol) or matching placebo in the daily drinking water. Four weeks later, 1H MRI and 31P magnetic resonance spectroscopy (MRS) were used to quantify in vivo functional and metabolic changes in postinfarction remodeled mouse myocardium and the effects of XOIs on that process. End-systolic (ESV) and end-diastolic volumes (EDV) were increased by more than sixfold after infarction, left ventricle (LV) mass doubled (P < 0.005), and the LV ejection fraction (EF) decreased (14 +/- 9%) compared with control hearts (59 +/- 8%, P < 0.005) at 1 mo. The myocardial phosphocreatine (PCr)-to-ATP ratio (PCr/ATP) was also significantly decreased in infarct remodeled hearts (1.4 +/- 0.6) compared with control animals (2.1 +/- 0.5, P < 0.02), in agreement with prior studies in larger animals. The XOIs allopurinol and oxypurinol did not change LV mass but limited the increase in ESV and EDV of infarct hearts by 50%, increased EF (23 +/- 9%, P = 0.01), and normalized cardiac PCr/ATP (2.0 +/- 0.5, P < 0.04). We conclude that XOIs improve ventricular function after infarction and normalize high-energy phosphate ratio in heart failure. Thus XOI therapy offers a new and potentially complementary approach to limit the adverse contractile and metabolic consequences after infarction.

Adenosine Triphosphate↗

PubMed2005

Cardioprotective role of the mitochondrial ATP-binding cassette protein 1.

The mechanism by which mitochondria exert protection against oxidant stress is not clear. We recently showed that a purified mitochondrial fraction containing 5 coimmunoprecipitating proteins (succinate dehydrogenase, adenine nucleotide translocator, ATP synthase, inorganic phosphate carrier, and mitochondrial ATP-binding cassette protein 1 or mABC1) displayed mitochondrial ATP-sensitive K+-channel activity. mABC1, a member of the ABC family of proteins, is the only protein in this complex whose function is not known. A yeast homologue of mABC1 protein, Mdl1p, was recently identified to have a novel role for induction of cellular resistance to oxidant stress. Based on these observations, we hypothesized that mABC1 plays a key role in protection of myocardial cells against oxidant stress. We studied the function of mABC1 by modulating the levels of this protein in neonatal rat cardiomyocytes using various molecular techniques, followed by assessment of cell viability and measurement of mitochondrial membrane potential. RNA interference resulted in reduced mABC1 mRNA and protein levels and was associated with significantly attenuated loss of tetramethylrhodamine ethyl ester fluorescence under basal conditions and an increase in trypan blue stained cells. In contrast, adenovirally mediated expression of mABC1 resulted in protection against oxidant stress loss of mitochondrial membrane potential. These results support the notion that mABC1 protein plays a major role in cellular protection against oxidant stress, identifying mABC1 as a novel target for cardioprotective therapeutics.

ATP Binding Cassette Transporter 1↗

PubMed2005

Antiarrhythmic engineering of skeletal myoblasts for cardiac transplantation.

Skeletal myoblasts are an attractive cell type for transplantation because they are autologous and resistant to ischemia. However, clinical trials of myoblast transplantation in heart failure have been plagued by ventricular tachyarrhythmias and sudden cardiac death. The pathogenesis of these arrhythmias is poorly understood, but may be related to the fact that skeletal muscle cells, unlike heart cells, are electrically isolated by the absence of gap junctions. Using a novel in vitro model of myoblast transplantation in cardiomyocyte monolayers, we investigated the mechanisms of transplant-associated arrhythmias. Cocultures of human skeletal myoblasts and rat cardiomyocytes resulted in reentrant arrhythmias (spiral waves) that reproduce the features of ventricular tachycardia seen in patients receiving myoblast transplants. These arrhythmias could be terminated by nitrendipine, an l-type calcium channel blocker, but not by the Na channel blocker lidocaine. Genetic modification of myoblasts to express the gap junction protein connexin43 decreased arrhythmogenicity in cocultures, suggesting a specific means for increasing the safety (and perhaps the efficacy) of myoblast transplantation in patients.

Action Potentials↗

PubMed2005

Non-equilibrium behavior of HCN channels: insights into the role of HCN channels in native and engineered pacemakers.

OBJECTIVE: I(f), encoded by the hyperpolarization-activated, cyclic nucleotide-modulated (HCN) channel gene family, modulates cardiac pacing. During cardiac pacing, changes in membrane potential are rapid, preventing the very slow HCN channels from reaching equilibrium. Here, we examined the properties of HCN channels under non-equilibrium conditions to shed insight into how different HCN isoforms contribute to cardiac pacing. METHODS AND RESULTS: HCN1, 2 and 4 channels were heterologously expressed in Xenopus laevis oocytes or mammalian Cos7 cells and subjected to voltage clamp. We found that HCN1 channel activation (V1/2) depended strongly on the holding potential (V(H)) for short (100 ms; V1/2=-118 mV, -78 mV and -19 mV for V(H)= +70, -75 and -140 mV, respectively, in Xenopus oocytes) but not long (300-ms) test-pulses, hinting that shifts of V1/2 under non-equilibrium conditions may alter the impact of I(f) in different phases of the cardiac circle. Consistent with this notion, when a train of SA nodal-like action potentials was applied in voltage-clamp experiments, HCN1 exhibited pronounced current-voltage (IV)-hysteresis. Using computational modeling, we demonstrate that the intrinsically sluggish HCN1 activation kinetics underlie their IV-hysteretic behavior and do not hinder the ability to modulate cardiac pacing. By contrast, HCN4 did not exhibit IV-hysteresis. This difference can be attributed to the relatively large activation time constant and markedly delayed onsets of time-dependent HCN4 currents. Indeed, HCN2 channels, which have intermediate activation time constants and delays, displayed and intermediate hysteretic phenotype. CONCLUSION: We conclude that non-equilibrium properties of HCN channels contribute to cardiac pacing. These results provide insight for tuning the firing rate of endogenous and induced pacemakers using engineered HCN constructs with distinct gating phenotypes.

Action Potentials↗

PubMed2005

Molecular correlates of altered expression of potassium currents in failing rabbit myocardium.

Action potential (AP) prolongation is a hallmark of failing myocardium. Functional downregulation of K currents is a prominent feature of cells isolated from failing ventricles. The detailed changes in K current expression differ depending on the species, the region of the heart, and the mechanism of induction of heart failure. We used complementary approaches to study K current downregulation in pacing tachycardia-induced heart failure in the rabbit. The AP duration (APD) at 90% repolarization was significantly longer in cells isolated from failing hearts compared with controls (539 +/- 162 failing vs. 394 +/- 114 control, P < 0.05). The major K currents in the rabbit heart, inward rectifier potassium current (I(K1)), transient outward (I(to)), and delayed rectifier current (I(K)) were functionally downregulated in cells isolated from failing ventricles. The mRNA levels of Kv4.2, Kv1.4, KChIP2, and Kir2.1 were significantly downregulated, whereas the Kv4.3, Erg, KvLQT1, and minK were unaltered in the failing ventricles compared with the control left ventricles. Significant downregulation in the long splice variant of Kv4.3, but not in the total Kv4.3, Kv4.2, and KChIP2 immunoreactive protein, was observed in cells isolated from the failing ventricle with no change in Kv1.4, KvLQT1, and in Kir2.1 immunoreactive protein levels. Multiple cellular and molecular mechanisms underlie the downregulation of K currents in the failing rabbit ventricle.

Action Potentials↗

PubMed2005

Optimization of IPG strip equilibration for the basic membrane protein mABC1.

Many proteins with extreme physical properties, including basic and acidic proteins, membrane proteins, and very large proteins, present specific challenges to 2-DE separation. Using a pressure-blotting approach, we demonstrate that a basic integral membrane protein, mitochondrial ATP-binding cassette protein 1 (mABC1), focuses in the IPG strip, but fails to enter into the 2-D SDS-PAGE gel. Through modifying the equilibration conditions between the IPG strip and 2nd dimension, we demonstrate that only by increasing both the volume (from 3 to 6 mL for a 7-cm strip) and SDS concentration (from 2 to 10%) of the equilibration buffer is migration of mABC1 into the 2nd dimension achieved. While 2-DE remains one of the core separation technologies of proteomic analysis, proteins that are extremely basic, hydrophobic, or of large mass present significant challenges to 2-DE separation due to aggregation, oxidation, precipitation, and the physical limitations of the 1-D IPG strip. Since the advent of commercially available IPG strips, numerous groups have experimented with IEF conditions using various detergents alone or in combination, alternative denaturants, and thiol oxidation agents to improve protein focusing. Effective 2-DE separation of membrane proteins has been affected dramatically by these advances in protein solubilization, as well as improvements in isolation of membranes, delipidation, and active in-gel rehydration. Since the development of commercially available basic IPG strips, the most significant advance in the separation of basic proteins has been the introduction of hydroxyethyldisulfides, either alone or in combination with DTT. While hydrophobic proteins were once virtually absent from the 2-D gel, and basic proteins were only visible as dense streaks, now many groups are undertaking large-scale analyses of membranes and basic proteins. Using this base of experimental tools, we embarked on a proteomic analysis of cardiac mitochondrial membranes, hoping to combine the knowledge gained from ongoing targeted protein chemistry and molecular biology studies with a broader-based proteomic analysis. Of particular interest is the inner mitochondrial membrane protein mABC1 (mitochondrial ATP-binding cassette protein 1), which may play a significant role in cardioprotection as part of the mitochondrial ATP-sensitive potassium channels. Therefore, in designing our 2-DE approach, it was crucial to ensure that mABC1 is focused, observable, and quantifiable, despite being an integral membrane protein of pI 9.37.

ATP Binding Cassette Transporter 1↗

PubMed2004

Functional integration of electrically active cardiac derivatives from genetically engineered human embryonic stem cells with quiescent recipient ventricular cardiomyocytes: insights into the development of cell-based pacemakers.

BACKGROUND: Human embryonic stem cells (hESCs) derived from blastocysts can propagate indefinitely in culture while maintaining pluripotency, including the ability to differentiate into cardiomyocytes (CMs); therefore, hESCs may provide an unlimited source of human CMs for cell-based therapies. Although CMs can be derived from hESCs ex vivo, it remains uncertain whether a functional syncytium can be formed between donor and recipient cells after engraftment. METHODS AND RESULTS: Using a combination of electrophysiological and imaging techniques, here we demonstrate that electrically active, donor CMs derived from hESCs that had been stably genetically engineered by a recombinant lentivirus can functionally integrate with otherwise-quiescent, recipient, ventricular CMs to induce rhythmic electrical and contractile activities in vitro. The integrated syncytium was responsive to the beta-adrenergic agonist isoproterenol as well as to other pharmacological agents such as lidocaine and ZD7288. Similarly, a functional hESC-derived pacemaker could be implanted in the left ventricle in vivo. Detailed optical mapping of the epicardial surface of guinea pig hearts transplanted with hESC-derived CMs confirmed the successful spread of membrane depolarization from the site of injection to the surrounding myocardium. CONCLUSIONS: We conclude that electrically active, hESC-derived CMs are capable of actively pacing quiescent, recipient, ventricular CMs in vitro and ventricular myocardium in vivo. Our results may lead to an alternative or a supplemental method for correcting defects in cardiac impulse generation, such as cell-based pacemakers.

Action Potentials↗

PubMed2004

Chronic treatment with allopurinol boosts survival and cardiac contractility in murine postischemic cardiomyopathy.

Oxidative stress is a hallmark of systemic illnesses, including heart failure. Nevertheless, the overall importance of radical production in the heart remains conjectural; is it merely a marker of illness, or can intervention alter the progression of disease? This question was addressed by blocking xanthine oxidase (XO), a superoxide-generating enzyme that is upregulated in animal models of heart failure. In a randomized prospective trial design, we administered the XO inhibitor allopurinol orally to mice that had undergone massive myocardial infarction (MI). Cardiac XO activity was elevated in untreated mice after MI; allopurinol suppressed the XO activity to levels comparable to those in sham-operated mice. Eighty-one percent of untreated mice died of advanced heart failure over 2 to 4 weeks of follow-up. Survival doubled in the allopurinol-treated mice, whereas cardiac contractile function (both in vivo and in isolated muscle) was markedly improved. Response to isoproterenol was restored to near-normal levels in the allopurinol group but was attenuated in untreated mice. Oxidative modifications to proteins were prevented in the allopurinol-treated mice. Our findings indicate that targeted blockade of just one source of oxidants, XO, impacts dramatically on the progression of postischemic cardiomyopathy in mice and prevents oxidative protein modifications.

Actin Cytoskeleton↗

PubMed2004

Multiprotein complex containing succinate dehydrogenase confers mitochondrial ATP-sensitive K+ channel activity.

The mitochondrial ATP-sensitive K(+) (mitoK(ATP)) channel plays a central role in protection of cardiac and neuronal cells against ischemia and apoptosis, but its molecular structure is unknown. Succinate dehydrogenase (SDH) is inhibited by mitoK(ATP) activators, fueling the contrary view that SDH, rather than mitoK(ATP), is the target of cardioprotective drugs. Here, we report that SDH forms part of mitoK(ATP) functionally and structurally. Four mitochondrial proteins [mitochondrial ATP-binding cassette protein 1 (mABC1), phosphate carrier, adenine nucleotide translocator, and ATP synthase] associate with SDH. A purified IM fraction containing these proteins was reconstituted into proteoliposomes and lipid bilayers and shown to confer mitoK(ATP) channel activity. This channel activity is sensitive not only to mitoK(ATP) activators and blockers but also to SDH inhibitors. These results reconcile the controversy over the basis of ischemic preconditioning by demonstrating that SDH is a component of mitoK(ATP) as part of a macromolecular supercomplex. The findings also provide a tangible clue as to the structural basis of mitoK(ATP) channels.

Adenosine Triphosphate↗

PubMed2004

Creation of a genetic calcium channel blocker by targeted gem gene transfer in the heart.

Calcium channel blockers are among the most commonly used therapeutic drugs. Nevertheless, the utility of calcium channel blockers for heart disease is limited because of the potent vasodilatory effect that causes hypotension, and other side effects attributable to blockade of noncardiac channels. Therefore, focal calcium channel blockade by gene transfer is highly desirable. With a view to creating a focally applicable genetic calcium channel blocker, we overexpressed the ras-related small G-protein Gem in the heart by somatic gene transfer. Adenovirus-mediated delivery of Gem markedly decreased L-type calcium current density in ventricular myocytes, resulting in the abbreviation of action potential duration. Furthermore, transduction of Gem resulted in a significant shortening of the electrocardiographic QTc interval and reduction of left ventricular systolic function. Focal delivery of Gem to the atrioventricular (AV) node significantly slowed AV nodal conduction (prolongation of PR and AH intervals), which was effective in the reduction of heart rate during atrial fibrillation. Thus, these results indicate that gene transfer of Gem functions as a genetic calcium channel blocker, the local application of which can effectively modulate cardiac electrical and contractile function.

Action Potentials↗

PubMed2004

Mutual functional destruction of HIV-1 Vpu and host TASK-1 channel.

Sequence analysis predicted significant structural homology between the HIV-1 accessory protein Vpu and the N-terminal region of TASK-1, a mammalian background K(+) channel. If the homology resulted from molecular piracy during HIV-1 evolution, these two proteins may have important functional interactions. Here we demonstrate that TASK and Vpu physically interact in cultured cells and in AIDS lymphoid tissues. The functional consequences were potentially destructive for both components: Vpu abolished TASK-1 current, while overexpressing TASK led to a marked impairment of Vpu's ability to enhance viral particle release. Further, the first 40 amino acids of TASK-1 (part of the homology to Vpu) were capable of enhancing HIV-1 particle release. This virus-host interaction may influence HIV-1/AIDS progression, as well as electrical signaling in infected host tissues.

Amino Acid Sequence↗