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U C Hoppe

Publications and source records attributed to U C Hoppe.

36 records · Page 2Linked to original sources
PubMed2001

Functional consequences of the arrhythmogenic G306R KvLQT1 K+ channel mutant probed by viral gene transfer in cardiomyocytes.

IKs, the slow component of the delayed rectifier potassium current, figures prominently in the repolarization of heart cells. The K+ channel gene KvLQT1 is mutated in the heritable long QT (LQT) syndrome. Heterologous coexpression of KvLQT1 and the accessory protein minK yields an IKs-like current. Nevertheless, the links between KvLQT1 and cardiac IKs are largely inferential. Since the LQT syndrome mutant KvLQT1-G306R suppresses channel activity when coexpressed with wild-type KvLQT1 in a heterologous system, overexpression of this mutant in cardiomyocytes should reduce or eliminate native IKs if KvLQT1 is indeed the major molecular component of this current. To test this idea, we created the adenovirus AdRMGI-KvLQT1-G306R, which overexpresses KvLQT1-G306R channels. In > 60 % of neonatal mouse myocytes, a sizable IKs could be measured using perforated-patch recordings (8.0 +/- 1.6 pA pF-1, n = 13). IKs was increased by forskolin and blocked by clofilium or indapamide but not by E-4031. While cells infected with a reporter virus expressing only green fluorescent protein (GFP) displayed IKs similar to that in uninfected cells, AdRMGI-KvLQT1-G306R-infected cells showed a significantly reduced IKs (2.4 +/- 1.1 pA pF-1, n = 10, P < 0.01) when measured 60-72 h after infection. Similar results were observed in adult guinea-pig myocytes (5.9 +/- 1.2 pA pF-1, n = 9, for control vs. 0.1 +/- 0.1 pA pF-1, n = 5, for AdRMGI-KvLQT1-G306R-infected cells). We conclude that KvLQT1 is the major molecular component of IKs. Our results further establish a dominant-negative mechanism for the G306R LQT syndrome mutation.

1-Methyl-3-isobutylxanthine↗
PubMed2001

Distinct gene-specific mechanisms of arrhythmia revealed by cardiac gene transfer of two long QT disease genes, HERG and KCNE1.

The long QT syndrome (LQTS) is a heritable disorder that predisposes to sudden cardiac death. LQTS is caused by mutations in ion channel genes including HERG and KCNE1, but the precise mechanisms remain unclear. To clarify this situation we injected adenoviral vectors expressing wild-type or LQT mutants of HERG and KCNE1 into guinea pig myocardium. End points at 48-72 h included electrophysiology in isolated myocytes and electrocardiography in vivo. HERG increased the rapid component, I(Kr), of the delayed rectifier current, thereby accelerating repolarization, increasing refractoriness, and diminishing beat-to-beat action potential variability. Conversely, HERG-G628S suppressed I(Kr) without significantly delaying repolarization. Nevertheless, HERG-G628S abbreviated refractoriness and increased beat-to-beat variability, leading to early afterdepolarizations (EADs). KCNE1 increased the slow component of the delayed rectifier, I(Ks), without clear phenotypic sequelae. In contrast, KCNE1-D76N suppressed I(Ks) and markedly slowed repolarization, leading to frequent EADs and electrocardiographic QT prolongation. Thus, the two genes predispose to sudden death by distinct mechanisms: the KCNE1 mutant flagrantly undermines cardiac repolarization, and HERG-G628S subtly facilitates the genesis and propagation of premature beats. Our ability to produce electrocardiographic long QT in vivo with a clinical KCNE1 mutation demonstrates the utility of somatic gene transfer in creating genotype-specific disease models.

Action Potentials↗
PubMed2000

Viral gene transfer of dominant-negative Kv4 construct suppresses an O2-sensitive K+ current in chemoreceptor cells.

Hypoxia initiates the neurosecretory response of the carotid body (CB) by inhibiting one or more potassium channels in the chemoreceptor cells. Oxygen-sensitive K(+) channels were first described in rabbit CB chemoreceptor cells, in which a transient outward K(+) current was reported to be reversibly inhibited by hypoxia. Although progress has been made to characterize this current with electrophysiological and pharmacological tools, no attempts have been made to identify which Kv channel proteins are expressed in rabbit CB chemoreceptor cells and to determine their contribution to the native O(2)-sensitive K(+) current. To probe the molecular identity of this current, we have used dominant-negative constructs to block the expression of functional Kv channels of the Shaker (Kv1.xDN) or the Shal (Kv4.xDN) subfamilies, because members of these two subfamilies contribute to the transient outward K(+) currents in other preparations. Delivery of the constructs into chemoreceptor cells has been achieved with adenoviruses that enabled ecdysone-inducible expression of the dominant-negative constructs and reporter genes in polycistronic vectors. In voltage-clamp experiments, we found that, whereas adenoviral infections of chemoreceptor cells with Kv1.xDN did not modify the O(2)-sensitive K(+) current, infections with Kv4.xDN suppressed the transient outward current in a time-dependent manner, significantly depolarized the cells, and abolished the depolarization induced by hypoxia. Our work demonstrate that genes of the Shal K(+) channels underlie the transient outward, O(2)-sensitive, K(+) current of rabbit CB chemoreceptor cells and that this current contributes to the cell depolarization in response to low pO(2).

Adenoviridae↗
PubMed2000

Adenovirus-mediated inducible gene expression in vivo by a hybrid ecdysone receptor.

Precise control of transgene expression would markedly facilitate certain applications of gene therapy. To regulate expression of a transferred gene in response to an exogenous compound in vivo, we modified the ecdysone-responsive system. We combined the advantages of the Drosophila (DmEcR) and the Bombyx ecdysone receptor (BmEcR) by creating a chimeric Drosophila/Bombyx ecdysone receptor (DB-EcR) that preserved the ability to bind to the modified ecdysone promoter without exogenous retinoid X receptor (RXR). In cultured cells, DB-EcR effectively mediates ligand-dependent transactivation of a reporter gene at lower concentrations of the chemical ecdysone agonist GS-E than VgRXR (DmEcR + RXR). Transgene delivery in vivo was achieved by intramyocardial injection of recombinant adenovirus vectors in adult rats. Upon stimulation with GS-E, DB-EcR potently (>40-fold induction) activated gene expression in vivo while VgRXR was not induced. This hybrid ecdysone receptor represents an important new tool for in vivo transgene regulation with potentially diverse applications in somatic and germline transfer.

Adenoviridae↗
PubMed2000

Infarct related artery patency: relation to serial electropharmacological studies and outcome in patients with previous myocardial infarction and ventricular tachyarrhythmias.

Evidence suggests that infarct related artery (IRA) patency may improve survival after acute myocardial infarction, which is thought to be partially due to a lower incidence of malignant ventricular tachyarrhythmias. However, little is known about the effect of IRA patency on antiarrhythmic drug response and long-term outcome in patients with previous infarction who already experienced sustained ventricular tachyarrhythmias. A total of 152 patients with remote myocardial infarction and documented ventricular tachycardia (VT) or ventricular fibrillation (VF) underwent coronary angiography and programmed ventricular stimulation before and after oral administration of d,l-sotalol (240-640 mg/day). D,l-sotalol suppressed inducibility of VT/VF in 37 (25.2%) patients. The IRA was patent in 38.1% of all patients. There was no significant difference in the frequency of drug response between patients with patent or occluded IRAs (26.8% vs 24.2%, P = 0.87). In patients with a patent IRA, d,l-sotalol tended to be more effective in the absence of a left ventricular aneurysm, although this difference did not reach statistical significance (P = 0.38). Ejection fraction and collateral blood flow had no effect on drug response in the presence or absence of IRA patency. During follow-up (13.0 +/- 19.9 months) of 29 patients discharged on oral d,l-sotalol, 3 patients experienced symptomatic VT and 4 sudden death. Arrhythmia recurrence and death of all cause (n = 6) and cardiac death (n = 4) were independent of IRA patency status. IRA patency had no effect on short-term drug response to d,l-sotalol in patients with remote myocardial infarction and documented VT/VF. Long-term outcome of patients with sustained ventricular tachyarrhythmias is independent of IRA patency status. In contrast to a previous report, outcome of electropharmacological testing was not predicted by the patency of the IRA.

Aged↗
PubMed2000

Molecular dissection of cardiac repolarization by in vivo Kv4.3 gene transfer.

Heart failure leads to marked suppression of the Ca(2+)-independent transient outward current (I(to1)), but it is not clear whether I(to1) downregulation suffices to explain the concomitant action potential prolongation. To investigate the role of I(to1) in cardiac repolarization while circumventing culture-related action potential alterations, we injected adenovirus vectors in vivo to overexpress or to suppress I(to1) in guinea pigs and rats, respectively. Myocytes were isolated 72 hours after intramyocardial injection and stimulation of the ecdysone-inducible vectors with intraperitoneal injection of an ecdysone analog. Kv4.3-infected guinea pig myocytes exhibited robust transient outward currents. Increasing density of I(to1) progressively depressed the plateau potential in Kv4. 3-infected guinea pig myocytes and abbreviated action potential duration (APD). In vivo infection with a dominant-negative Kv4. 3-W362F construct suppressed peak I(to1) in rat ventriculocytes, elevated the plateau height, significantly prolonged the APD, and resulted in a prolongation by about 30% of the QT interval in surface electrocardiogram recordings. These results indicate that I(to1) plays a crucial role in setting the plateau potential and overall APD, supporting a causative role for suppression of this current in the electrophysiological alterations of heart failure. The electrocardiographic findings indicate that somatic gene transfer can be used to create gene-specific animal models of the long QT syndrome.

Animals↗
PubMed1999

Manipulation of cellular excitability by cell fusion: effects of rapid introduction of transient outward K+ current on the guinea pig action potential.

To investigate the still-undetermined role of the Ca2+-independent transient outward current (Ito1) on repolarization of the cardiac action potential, we used cell fusion to introduce Ito1 into guinea pig cardiomyocytes, which normally lack this current. This technique enables the rapid delivery of premade functional ion channels to cardiomyocytes within hours of isolation, thus eliminating the action potential alterations that complicate prolonged cell culture. Chinese hamster ovary (CHO) cells stably expressing Kv4.3 (CHO-Kv4. 3) were loaded with a fluorescent dye and fused to guinea pig cardiomyocytes using polyethylene glycol. As controls, nontransfected CHO cells were fused using the same protocol. Myocytes fused with CHO-Kv4.3 cells exhibited a robust Ito1 (16. 5+/-2.6 pA/pF at +40 mV; 37 degrees C; n=19), whereas controls had none. Ito1 accelerated the early repolarization velocity (r=-0.68; 3 ms after the overshoot) and progressively suppressed the voltage of the plateau phase (r=-0.90) with increasing Ito1 density. Reduction of the action potential duration to 50% repolarization (r=-0.76) and to 90% repolarization (r=-0.65) also correlated well with Ito1 density. Thus, Ito1 exerted a significant effect on the early repolarization phase and abbreviated action potential duration. Cell fusion is a valuable and generalizable technique to introduce preformed membrane proteins into native cells.

Action Potentials↗
PubMed1998

Modulation of the hyperpolarization-activated inward current (If) by antiarrhythmic agents in isolated human atrial myocytes.

The hyperpolarization-activated inward current (If) has been discussed to contribute to arrhythmias in human atrial myocardium. If was found to be increased by beta-adrenergic stimulation. In the present study, we evaluate the modulation of If by carbachol, adenosine and by class Ic, III and IV antiarrhythmic drugs in isolated human atrial myocytes. The whole-cell patch-clamp technique was used to record If in isolated myocytes from 18 human right atrial appendages. A typical time- and voltage-dependent hyperpolarization-activated inward current could be recorded in all cells investigated (n=56). Mean current density recorded at -130 mV was -2.8+/-1.2 pApF(-1). Both adenosine and carbachol were found to directly inhibit If in human atrial myocytes by shifting the activation curves to more negative potentials. Adenosine 10(-5) mol/l shifted the potential of half-maximal activation by -5.9+/-0.4 mV from -99.4+/-0.6 mV to -105.3+/-0.4 mV (n=8; P<0.05), and carbachol 10(-5) mol/l by -5.7+/-0.5 mV from -99.2+/-0.5 mV to -104.9+/-0.6 mV (n=6; P<0.05). The concentration-response curve of adenosine calculated by a Hill function yielded a half-maximal effect of adenosine (EC50) at a concentration of 3.6+/-0.5 micromol/l, a maximal shift of -6.5+/-0.3 mV, and a Hill coefficient (h) of 2.40. We did not observe any effect of flecainide (10(-5) mol/l; n=8), sotalol (10(-5) mol/l; n=6), amiodarone (10(-5) mol/l; n=6) or verapamil (10(-5) mol/l; n=5) on If in human atrial myocytes. However, propafenone (10(-5) mol/l) was found to reversibly reduce If current size (9/13 cells) by shifting the activation curve by -5.2+/-0.4 mV (P<0.05). In human atria adenosine- and muscarinic receptor stimulation might function as endogenous protective mechanisms inhibiting the initiation of ectopic tachycardia by reducing If current size. Propafenone may be more effective in some patients with atrial tachycardias that do not respond to other class Ic, III and IV antiarrhythmic drugs. However, it has yet to be defined whether these agents suppress atrial tachycardias via an inhibition of If in vivo.

Adenosine↗
PubMed1998

Characterization of the hyperpolarization-activated inward current in isolated human atrial myocytes.

OBJECTIVE: The hyperpolarization-activated inward current (I(f)) has been discussed to contribute to arrhythmias in rat hypertrophied and human failing ventricular myocardium. Cat atrial myocytes were found to exhibit variable size of I(f). In the present study, we evaluate characteristics of I(f) in human atrial myocardium and investigate if human atria might exhibit any electrophysiological heterogeneity in the diastolic voltage range. METHODS AND RESULTS: The whole-cell patch-clamp technique was used to record I(f) in isolated myocytes from 96 human right atrial appendages. I(f) was observed in 95% (ruptured-patch; 141/146) to 100% (perforated-patch; 18/18) of myocytes showing typical current properties, i.e. time- and voltage-dependence, block by [Cs+]o, permeability for K+, Na+ and Li+, and current increase with raising [K+]o. Using the perforated-patch technique Boltzmann distributions yielded an activation threshold of -60 to -70 mV and half maximal activation at -89.3 +/- 0.7 mV (n = 18). Isoproterenol (10(-6) mol/l) shifted I(f) activation by +7 mV (7/7) using the perforated-patch technique, but only inconsistently shifted I(f) activation using the ruptured-patch method (6/21). Based on the relative current size of I(f) and IK1 three cell types could be distinguished (n = 26). In myocytes with a prominent I(f), I(f) density was found to be larger (in [K+]o 25 mmol/l at -80 mV: -0.78 +/- 0.23 pApF-1; n = 7) than in cells with predominant IK1 (in [K+]o 25 mmol/l at -80 mV: -0.02 +/- 0.01 pApF-1; n = 4) (P < 0.05). CONCLUSIONS: I(f) is present in most human atrial myocytes. Many current properties are similar to those described for I(f) in mammalian pacemaker cells. The relative current size of I(f) and IK1 were found to be variable in different myocytes. Whether I(f) may favor spontaneous diastolic depolarization in individual human atrial myocytes exhibiting predominantly I(f) in vivo remains to be defined, as current size is very small under physiological [K+]o.

Adrenergic beta-Agonists↗
PubMed1997

[Contusio cordis--too seldom diagnosed?].

BACKGROUND: Myocardial contusion is the most common injury caused by blunt chest trauma. Cardiac contusion often does not produce significant symptoms and, thus, remains unrecognized. CASE REPORT: A 29-year-old professional ice-hockey player presented with a tachyarrhythmia two days after having suffered a thoracic trauma. Two weeks prior to admission he had an influenza-like infection. Non-invasive diagnostic methods were normal. However, cardiac catheterization revealed an akinesis of the left ventricular anterior wall in the absence of any coronary artery lesions. Endomyocardial biopsy did not show any evidence of myocarditis but erythrocyte extravasations in the endo- and myocardium, thus, confirming the diagnosis of cardiac contusion. Three months later, left ventriculography and coronary angiography did neither demonstrate any abnormalities of ventricular contraction nor of the coronary vessels. CONCLUSION: Myocardial contusion is still being rarely diagnosed after sporting accidents. Cardiac contusion is a benign disorder in most patients. However, due to its potentially lethal outcome and as sequelae may present late after the trauma, early and precise diagnosis is important, both from the clinical point of view as well as for future insurance requests. Thus, invasive diagnostic techniques should be performed when non-invasive examinations do not provide a conclusive diagnosis.

Adult↗
PubMed1996

Congenital heart disease in adults and adolescents: comparative value of transthoracic and transesophageal echocardiography and MR imaging.

PURPOSE: To compare the diagnostic value of transesophageal echocardiography and magnetic resonance (MR) imaging with that of transthoracic echocardiography in the evaluation of congenital heart disease in adults and adolescents. MATERIALS AND METHODS: Corresponding transesophageal echocardiographic and MR images obtained in 61 patients (aged 14-74 years; 28 female, 33 male) with congenital cardiac abnormalities were analyzed retrospectively. Results were compared with those of transthoracic echocardiography in all patients and were confirmed by using cardiac catheterization (n = 41) and/or surgery (n = 41). RESULTS: of the 344 abnormalities detected with at least one imaging technique, 259 were demonstrated with transthoracic echocardiography. Transesophageal echocardiography depicted the atrioventricular junction and atrial structures the best. MR imaging was the only technique to fully depict 31 extracardiac abnormalities. In complex cardiac defects, the combination of all three imaging techniques was best. CONCLUSION: Transesophageal echocardiography and MR imaging are beneficial complementary imaging techniques in adults or adolescents with congenital heart disease.

Adolescent↗
PubMedDate not supplied

Hyperpolarization-activated inward current in ventricular myocytes from normal and failing human hearts.

BACKGROUND: The hyperpolarization-activated inward current (I[f]) was found to be overexpressed in hypertrophied rat ventricular myocytes, indicating that I(f) might favor arrhythmias in hypertrophied or failing ventricular myocardium. In the present study, we evaluated whether I(f) is expressed in human ventricular myocardium, if it may be increased in human heart failure, and if its autonomic modulation may be altered. METHODS AND RESULTS: The whole-cell patch-clamp technique was used to record I(f) in isolated ventricular myocytes from 34 failing (dilated [DCM] or ischemic [ICM] cardiomyopathy) and 13 donor hearts (NF). I(f) was observed in all myocytes showing typical current properties, ie, time and voltage dependence, block by [Cs+]o, permeability for K+ and Na+, and current increase with raising [K+]o. There was a trend toward larger current densities in myopathic (at -130 mV in [K+]o 25 mmol/L; DCM: -1.37 +/- 0.12 pA/pF, n = 50; ICM: -1.39 +/- 0.24 pA/pF, n = 30) than in nonfailing cells (-1.18 +/- 0.21 pA/pF, n = 24), although this difference did not reach statistical significance (P=.23). Boltzmann distributions yielded an activation threshold of -80 mV and half-maximal activation at -110.96 +/- 0.06 mV in myopathic and normal myocytes. Isoproterenol (10(-5) mol/L) shifted the current activation by 10 mV (31 myopathic, 5 NF). Carbachol and adenosine had no direct effect on I(f) (6 and 12 myopathic, 3 and 3 NF, respectively) but reversibly antagonized beta-adrenergic stimulation (5 and 7 myopathic, 2 and 2 NF, respectively). Autonomic modulation was similar in failing and nonfailing cells. CONCLUSIONS: In end-stage heart failure, no significant change of I(f) could be found, although there was a trend toward increased I(f). Together with an elevated plasma norepinephrine concentration and a previously reported reduction in I(K1) in human heart failure, I(f) might favor diastolic depolarization in individual myopathic cells.

Action Potentials↗