Publications by authors named "Brigitte Pelzmann"

19 Publications

  • Page 1 of 1

A549 in-silico 1.0: A first computational model to simulate cell cycle dependent ion current modulation in the human lung adenocarcinoma.

PLoS Comput Biol 2021 Jun 22;17(6):e1009091. Epub 2021 Jun 22.

Institute of Health Care Engineering with European Testing Center for Medical Devices, Graz University of Technology, Graz, Austria.

Lung cancer is still a leading cause of death worldwide. In recent years, knowledge has been obtained of the mechanisms modulating ion channel kinetics and thus of cell bioelectric properties, which is promising for oncological biomarkers and targets. The complex interplay of channel expression and its consequences on malignant processes, however, is still insufficiently understood. We here introduce the first approach of an in-silico whole-cell ion current model of a cancer cell, in particular of the A549 human lung adenocarcinoma, including the main functionally expressed ion channels in the plasma membrane as so far known. This hidden Markov-based model represents the electrophysiology behind proliferation of the A549 cell, describing its rhythmic oscillation of the membrane potential able to trigger the transition between cell cycle phases, and it predicts membrane potential changes over the cell cycle provoked by targeted ion channel modulation. This first A549 in-silico cell model opens up a deeper insight and understanding of possible ion channel interactions in tumor development and progression, and is a valuable tool for simulating altered ion channel function in lung cancer electrophysiology.
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http://dx.doi.org/10.1371/journal.pcbi.1009091DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8219159PMC
June 2021

GIRK1 triggers multiple cancer-related pathways in the benign mammary epithelial cell line MCF10A.

Sci Rep 2019 12 17;9(1):19277. Epub 2019 Dec 17.

Gottfried Schatz Research Center for Cell Signaling, Metabolism and Aging, Medical University of Graz, Graz, Austria.

Excessive expression of subunit 1 of GIRK1 in ER breast tumors is associated with reduced survival times and increased lymph node metastasis in patients. To investigate possible tumor-initiating properties, benign MCF10A and malign MCF7 mammary epithelial cells were engineered to overexpress GIRK1 neoplasia associated vital parameters and resting potentials were measured and compared to controls. The presence of GIRK1 resulted in resting potentials negative to the controls. Upon GIRK1 overexpression, several cellular pathways were regulated towards pro-tumorigenic action as revealed by comparison of transcriptomes of MCF10A with the control (MCF10A). According to transcriptome analysis, cellular migration was promoted while wound healing and extracellular matrix interactions were impaired. Vital parameters in MCF7 cells were affected akin the benign MCF10A lines, but to a lesser extent. Thus, GIRK1 regulated cellular pathways in mammary epithelial cells are likely to contribute to the development and progression of breast cancer.
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http://dx.doi.org/10.1038/s41598-019-55683-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6917815PMC
December 2019

Saxagliptin but Not Sitagliptin Inhibits CaMKII and PKC via DPP9 Inhibition in Cardiomyocytes.

Front Physiol 2018 14;9:1622. Epub 2018 Nov 14.

Division of Cardiology, Medical University of Graz, Graz, Austria.

Some oral anti-hyperglycemic drugs, including gliptins that inhibit dipeptidyl peptidase 4 (DPP4), have been linked to the increased risk of heart failure (HF) in type-2 diabetic patients. While the cardiovascular safety trial, TECOS, revealed no link between sitagliptin and the risk of HF, a substantial 27% increase in the hospitalization for HF was observed in type-2 diabetic patients treated with saxagliptin within the SAVOR-TIMI 53 trial. A previous study revealed that saxagliptin impairs the Ca/calmodulin-dependent protein kinase II (CaMKII)-phospholamban (PLB)-sarcoplasmic reticulum Ca-ATPase 2a axis and protein kinase C (PKC) activity in cardiomyocytes leading to impaired cardiac contractility and electrophysiological function. However, the link between saxagliptin and its target proteins (CaMKII and PKC) remains to be explored. Since DPP8 and DPP9 (but not DPP4) are expressed by cardiomyocytes and saxagliptin is internalized by cardiomyocytes, we investigated whether DPP8/9 contribute to saxagliptin-mediated inhibition of CaMKII and PKC activity. Structural analysis revealed that the DPP4-saxagliptin interaction motif (S630, Y547) for the cyanopyrrolidine group is conserved in DPP8 (S755, Y669) and DPP9 (S730, Y644). Conversely, F357 that facilitates binding of the anchor lock domain of sitagliptin in the S2 extensive subsite of DPP4 is not conserved in DPP8/9. In parallel, unlike saxagliptin, sitagliptin did not affect phosphorylation of CaMKII/PLB or activity of PKC in HL-1 cardiomyocytes. These findings were recapitulated by pharmacological inhibition (TC-E-5007, a DPP8/9 antagonist) and knock-down of DPP9 (but not DPP8). In primary mouse ventricular cardiomyocytes, saxagliptin (but not sitagliptin) impaired Ca transient relaxation and prolonged action potential duration (APD). These results suggest that saxagliptin-DPP9 interaction impairs the CaMKII-PLB and PKC signaling in cardiomyocytes. We reveal a novel and potential role of DPP9 in cardiac signaling. The interaction of saxagliptin with DPP9 may represent an underlying mechanism for the link between saxagliptin and HF. Elucidation of saxagliptin-DPP9 interaction and downstream events may foster a better understanding of the role of gliptins as modulators of cardiac signaling.
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http://dx.doi.org/10.3389/fphys.2018.01622DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6246635PMC
November 2018

Sinoatrial Beat to Beat Variability Assessed by Contraction Strength in Addition to the Interbeat Interval.

Front Physiol 2018 18;9:546. Epub 2018 May 18.

Institute of Biophysics, Medical University of Graz, Graz, Austria.

Beat to beat variability of cardiac tissue or isolated cells is frequently investigated by determining time intervals from electrode measurements in order to compute scale dependent or scale independent parameters. In this study, we utilize high-speed video camera recordings to investigate the variability of intervals as well as mechanical contraction strengths and relative contraction strengths with nonlinear analyses. Additionally, the video setup allowed us simultaneous electrode registrations of extracellular potentials. Sinoatrial node tissue under control and acetylcholine treated conditions was used to perform variability analyses by computing sample entropies and Higuchi dimensions. Beat to beat interval variabilities measured by the two recording techniques correlated very well, and therefore, validated the video analyses for this purpose. Acetylcholine treatment induced a reduction of beating rate and contraction strength, but the impact on interval variability was negligible. Nevertheless, the variability analyses of contraction strengths revealed significant differences in sample entropies and Higuchi dimensions between control and acetylcholine treated tissue. Therefore, the proposed high-speed video camera technique might represent a non-invasive tool that allows long-lasting recordings for detecting variations in beating behavior over a large range of scales.
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http://dx.doi.org/10.3389/fphys.2018.00546DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5968354PMC
May 2018

Molecular mimicking of C-terminal phosphorylation tunes the surface dynamics of Ca1.2 calcium channels in hippocampal neurons.

J Biol Chem 2018 01 27;293(3):1040-1053. Epub 2017 Nov 27.

From the Institute of Biophysics, Medical University of Graz, 8010 Graz, Austria,

L-type voltage-gated Ca1.2 calcium channels (Ca1.2) are key regulators of neuronal excitability, synaptic plasticity, and excitation-transcription coupling. Surface-exposed Ca1.2 distributes in clusters along the dendrites of hippocampal neurons. A permanent exchange between stably clustered and laterally diffusive extra-clustered channels maintains steady-state levels of Ca1.2 at dendritic signaling domains. A dynamic equilibrium between anchored and diffusive receptors is a common feature among ion channels and is crucial to modulate signaling transduction. Despite the importance of this fine regulatory system, the molecular mechanisms underlying the surface dynamics of Ca1.2 are completely unexplored. Here, we examined the dynamic states of Ca1.2 depending on phosphorylation on Ser-1700 and Ser-1928 at the channel C terminus. Phosphorylation at these sites is strongly involved in Ca1.2-mediated nuclear factor of activated T cells (NFAT) signaling, long-term potentiation, and responsiveness to adrenergic stimulation. We engineered Ca1.2 constructs mimicking phosphorylation at Ser-1700 and Ser-1928 and analyzed their behavior at the membrane by immunolabeling protocols, fluorescence recovery after photobleaching, and single particle tracking. We found that the phosphomimetic S1928E variant increases the mobility of Ca1.2 without altering the steady-state maintenance of cluster in young neurons and favors channel stabilization later in differentiation. Instead, mimicking phosphorylation at Ser-1700 promoted the diffusive state of Ca1.2 irrespective of the differentiation stage. Together, these results reveal that phosphorylation could contribute to the establishment of channel anchoring mechanisms depending on the neuronal differentiation state. Finally, our findings suggest a novel mechanism by which phosphorylation at the C terminus regulates calcium signaling by tuning the content of Ca1.2 at signaling complexes.
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http://dx.doi.org/10.1074/jbc.M117.799585DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5777246PMC
January 2018

Novel genetically encoded fluorescent probes enable real-time detection of potassium in vitro and in vivo.

Nat Commun 2017 11 10;8(1):1422. Epub 2017 Nov 10.

Institute of Molecular Biology and Biochemistry, Medical University of Graz, Neue Stiftingtalstraße 6/6, 8010, Graz, Austria.

Changes in intra- and extracellular potassium ion (K) concentrations control many important cellular processes and related biological functions. However, our current understanding of the spatiotemporal patterns of physiological and pathological K changes is severely limited by the lack of practicable detection methods. We developed K-sensitive genetically encoded, Förster resonance energy transfer-(FRET) based probes, called GEPIIs, which enable quantitative real-time imaging of K dynamics. GEPIIs as purified biosensors are suitable to directly and precisely quantify K levels in different body fluids and cell growth media. GEPIIs expressed in cells enable time-lapse and real-time recordings of global and local intracellular K signals. Hitherto unknown Ca-triggered, organelle-specific K changes were detected in pancreatic beta cells. Recombinant GEPIIs also enabled visualization of extracellular K fluctuations in vivo with 2-photon microscopy. Therefore, GEPIIs are relevant for diverse K assays and open new avenues for live-cell K imaging.
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http://dx.doi.org/10.1038/s41467-017-01615-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5681659PMC
November 2017

Dipeptidyl peptidase-4 independent cardiac dysfunction links saxagliptin to heart failure.

Biochem Pharmacol 2017 12 30;145:64-80. Epub 2017 Aug 30.

Department of Internal Medicine, Division of Cardiology, Medical University of Graz, Austria.

Saxagliptin treatment has been associated with increased rate of hospitalization for heart failure in type 2 diabetic patients, though the underlying mechanism(s) remain elusive. To address this, we assessed the effects of saxagliptin on human atrial trabeculae, guinea pig hearts and cardiomyocytes. We found that the primary target of saxagliptin, dipeptidyl peptidase-4, is absent in cardiomyocytes, yet saxagliptin internalized into cardiomyocytes and impaired cardiac contractility via inhibition of the Ca/calmodulin-dependent protein kinase II-phospholamban-sarcoplasmic reticulum Ca-ATPase 2a axis and Na-Ca exchanger function in Ca extrusion. This resulted in reduced sarcoplasmic reticulum Ca content, diastolic Ca overload, systolic dysfunction and impaired contractile force. Furthermore, saxagliptin reduced protein kinase C-mediated delayed rectifier K current that prolonged action potential duration and consequently QTc interval. Importantly, saxagliptin aggravated pre-existing cardiac dysfunction induced by ischemia/reperfusion injury. In conclusion, our novel results provide mechanisms for the off-target deleterious effects of saxagliptin on cardiac function and support the outcome of SAVOR-TIMI 53 trial that linked saxagliptin with the risk of heart failure.
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http://dx.doi.org/10.1016/j.bcp.2017.08.021DOI Listing
December 2017

Functional impairment of endothelial cells by the antimycotic amphotericin B.

Biochem Biophys Res Commun 2016 Mar 18;472(1):40-5. Epub 2016 Feb 18.

Institute of Biophysics, Medical University of Graz, Graz, Austria. Electronic address:

We set out to determine the membrane potential (Vm) of the endothelial cell line EA.hy926 and its sensitivity to the antimycotic amphotericin B (AmB), a commonly used antifungal component in cell culture media. We measured the endothelial Vm under various experimental conditions by patch clamp technique and found that Vm of AmB-treated cells is (-12.1 ± 9.3) mV, while in AmB-untreated (control) cells it is (-57.1 ± 4.1) mV. In AmB-free extracellular solutions, Vm recovered toward control levels and this gain in Vm rapidly dissipated upon re-addition of AmB, demonstrating a rapid and reversible effect of AmB on endothelial Vm. The consequences of AmB dependent alterations in endothelial transmembrane potential were tested at the levels of Ca(2+) signaling, of nucleotide concentrations, and energy metabolism. In AmB-treated cells we found substantially reduced Ca(2+) entry (to about 60% of that in control cells) in response to histamine induced endoplasmic reticulum (ER) Ca(2+) depletion, and diminished the ATP-to-ADP ratio (by >30%). Our data demonstrate a marked and experimentally relevant dependence of basic functional parameters of cultured endothelial cells on the presence of the ionophoric antimycotic AmB. The profound and reversible effects of the widely used culture media component AmB need careful consideration when interpreting experimental data obtained under respective culture conditions.
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http://dx.doi.org/10.1016/j.bbrc.2016.02.054DOI Listing
March 2016

Development of novel FP-based probes for live-cell imaging of nitric oxide dynamics.

Nat Commun 2016 Feb 4;7:10623. Epub 2016 Feb 4.

Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, Harrachgasse 21/III, 8010 Graz, Austria.

Nitric oxide () is a free radical with a wide range of biological effects, but practically impossible to visualize in single cells. Here we report the development of novel multicoloured fluorescent quenching-based probes by fusing a bacteria-derived -binding domain close to distinct fluorescent protein variants. These genetically encoded probes, referred to as geNOps, provide a selective, specific and real-time read-out of cellular dynamics and, hence, open a new era of bioimaging. The combination of geNOps with a Ca(2+) sensor allowed us to visualize and Ca(2+) signals simultaneously in single endothelial cells. Moreover, targeting of the probes was used to detect signals within mitochondria. The geNOps are useful new tools to further investigate and understand the complex patterns of signalling on the single (sub)cellular level.
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http://dx.doi.org/10.1038/ncomms10623DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4743004PMC
February 2016

The nitric oxide donor, S-nitroso human serum albumin, as an adjunct to HTK-N cardioplegia improves protection during cardioplegic arrest after myocardial infarction in rats.

Interact Cardiovasc Thorac Surg 2015 Mar 2;20(3):387-94. Epub 2014 Dec 2.

Department of Cardiac Surgery, LK St. Pölten, Pölten, Austria Ludwig Boltzmann Cluster for Cardiovascular Research, Vienna Medical University, Vienna, Austria.

Objectives: Currently available cardioplegic solutions provide excellent protection in patients with normal surgical risk; in high-risk patients, however, such as in emergency coronary artery bypass surgery, there is still room for improvement. As most of the cardioplegic solutions primarily protect myocytes, the addition of substances for protection of the endothelium might improve their protective potential. The nitric oxide donor, S-nitroso human serum albumin (S-NO-HSA), which has been shown to prevent endothelial nitric oxide synthase uncoupling, was added to the newly developed histidine-tryptophan-ketoglutarat (HTK-N) cardioplegia in an isolated heart perfusion system after subjecting rats to acute myocardial infarction (MI) and reperfusion.

Methods: In male Sprague-Dawley rats, acute MI was induced by ligation for 1 h of the anterior descending coronary artery. After 2 h of in vivo reperfusion hearts were evaluated on an isolated erythrocyte-perfused working heart model. Cold ischaemia (4°C) for 60 min was followed by 45 min of reperfusion. Cardiac arrest was induced either with HTK (n = 10), HTK-N (n = 10) or HTK-N + S-NO-HSA (n = 10). In one group (HTK-N + S-NO-HSA plus in vivo S-NO-HSA; n = 9) an additional in vivo infusion of S-NO-HSA was performed.

Results: Post-ischaemic recovery of cardiac output (HTK: 77 ± 4%, HTK-N: 86 ± 7%, HTK-N + S-NO-HSA: 101 ± 5%, in vivo S-NO-HSA: 93 ± 8%), external heart work (HTK: 79 ± 5%, HTK-N: 83 ± 3%, HTK-N + S-NO-HSA: 101 ± 8%, in vivo S-NO-HSA: 109 ± 13%), coronary flow (HTK: 77 ± 4%, HTK-N: 94 ± 6%, HTK-N + S-NO-HSA: 118 ± 15%, in vivo S-NO-HSA: 113 ± 3.17%) [HTK-N + S-NO-HSA vs HTK P < 0.001; HTK-N + S-NO-HSA vs HTK-N P < 0.05] and left atrial diastolic pressure (HTK: 122 ± 31%, HTK-N: 159 ± 43%, HTK-N + S-NO-HSA: 88 ± 30, in vivo S-NO-HSA: 62 ± 10%) [HTK-N + S-NO-HSA vs HTK P < 0.05; in vivo S-NO-HSA vs HTK-N P < 0.05] were significantly improved in both S-NO-HSA-treated groups compared with HTK and HTK-N, respectively. This was accompanied by better preservation of high-energy phosphates (adenosine triphosphate; energy charge) and ultrastructural integrity on transmission electron microscopy. However, no additional benefit of in vivo S-NO-HSA infusion was observed.

Conclusions: Addition of the NO donor, S-NO-HSA refines the concept of HTK-N cardioplegia in improving post-ischaemic myocardial perfusion. HTK-N with S-NO-HSA is a possible therapeutic option for patients who have to be operated on for acute MI.
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http://dx.doi.org/10.1093/icvts/ivu383DOI Listing
March 2015

I(f) blocking potency of ivabradine is preserved under elevated endotoxin levels in human atrial myocytes.

J Mol Cell Cardiol 2014 Jul 25;72:64-73. Epub 2014 Feb 25.

Institute of Biophysics, Medical University of Graz, Harrachgasse 21, A-8010 Graz, Austria. Electronic address:

Lower heart rate is associated with better survival in patients with multiple organ dysfunction syndrome (MODS), a disease mostly caused by sepsis. The benefits of heart rate reduction by ivabradine during MODS are currently being investigated in the MODIfY clinical trial. Ivabradine is a selective inhibitor of the pacemaker current If and since If is impaired by lipopolysaccharide (LPS, endotoxin), a trigger of sepsis, we aimed to explore If blocking potency of ivabradine under elevated endotoxin levels in human atrial cardiomyocytes. Treatment of myocytes with S-LPS (containing the lipid A moiety, a core oligosaccharide and an O-polysaccharide chain) but not R595 (an O-chain lacking LPS-form) caused If inhibition under acute and chronic septic conditions. The specific interaction of S-LPS but not R595 to pacemaker channels HCN2 and HCN4 proves the necessity of O-chain for S-LPS-HCN interaction. The efficacy of ivabradine to block If was reduced under septic conditions, an observation that correlated with lower intracellular ivabradine concentrations in S-LPS- but not R595-treated cardiomyocytes. Computational analysis using a sinoatrial pacemaker cell model revealed that despite a reduction of If under septic conditions, ivabradine further decelerated pacemaking activity. This novel finding, i.e. If inhibition by ivabradine under elevated endotoxin levels in vitro, may provide a molecular understanding for the efficacy of this drug on heart rate reduction under septic conditions in vivo, e.g. the MODIfY clinical trial.
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http://dx.doi.org/10.1016/j.yjmcc.2014.02.010DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4046244PMC
July 2014

Beat to beat variability of embryonic chick heart cells under septic conditions: application and evaluation of entropy as well as fractal measures.

Annu Int Conf IEEE Eng Med Biol Soc 2013 ;2013:5566-9

Extracardiac factors of heart rate variability have commonly been investigated using linear and nonlinear methods for a long time. Recently, intracardiac mechanisms on an electrophysiological basis have been found to be also important. This work is focused on the evaluation of complex measures of temporal signals gained with microelectrode measurements of embryonic chick heart aggregates. Septic conditions were mimicked in vitro by lipopolysaccharide (LPS) administration in order to investigate the influence on beat to beat variability. Surrogate data analysis revealed high statistical significances for normalized complexity measures.
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http://dx.doi.org/10.1109/EMBC.2013.6610811DOI Listing
July 2015

Effects of thienopyridines and thienopyrimidinones on L-type calcium current in isolated cardiomyocytes.

Naunyn Schmiedebergs Arch Pharmacol 2010 Dec 14;382(5-6):433-40. Epub 2010 Sep 14.

Institute of Biophysics, Center of Physiological Medicine, Medical University Graz, Harrachgasse 21/4, 8010, Graz, Austria.

Thienopyridines (ticlopidine, clopidogrel) are frequently used drugs in antiplatelet therapy and have been shown to exert a more pronounced negative inotropic effect than thienopyrimidinones. We hypothesized that these differences are due to a differential impact of thienopyridines and thienopyrimidinones on L-type calcium current at the single-cell level. The effects of thienopyridines and thienopyrimidinones were studied on L-type calcium current and action potential parameters with the whole-cell patch-clamp technique in isolated myocytes from guinea pig ventricle and human atrial appendage. Ticlopidine showed the greatest impact on the L-type calcium current in guinea pig myocytes. It significantly reduced L-type calcium current density as well as shifted half maximal inactivation potential to more negative potentials compared to clopidogrel (at 30 μmol/L) and to all thienopyrimidinones (30 and 100 μmol/L). Clopidogrel significantly reduced the L-type calcium current density as well as shifted the half maximal inactivation potential to more negative potentials compared to all thienopyrimidinones at 100 μmol/L only. In contrast, thienopyrimidinones did not affect L-type calcium current properties. The significant different effects of thienopyridines and thienopyrimidinones could also be demonstrated in human atrial myocytes. The more pronounced negative inotropic effect of thienopyridines is well explained by our results demonstrating a differential impairment of L-type calcium current by thienopyridines and thienopyrimidinones. L-type calcium current impairment by thienopyridines may be of special relevance for patients with cardiac diseases characterized by ionic remodelling.
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http://dx.doi.org/10.1007/s00210-010-0557-yDOI Listing
December 2010

Endotoxin impairs the human pacemaker current If.

Shock 2007 Dec;28(6):655-661

Institut für Biophysik, Zentrum für Physiologische Medizin, Medizinische Universität Graz, Harrachgasse 21, Graz, Austria.

LPSs trigger the development of sepsis by gram-negative bacteria and cause a variety of biological effects on host cells, including alterations on ionic channels. Because heart rate variability is reduced in human sepsis and endotoxemia, we hypothesized that LPS affects the pacemaker current I(f) in human heart, which might--at least in part--explain this phenomenon. Isolated human myocytes from right atrial appendages were incubated for 6 to 10 h with LPS (1 and 10 microg/mL) and afterwards used to investigate the pacemaker current I(f). I(f) was measured with the whole-cell patch-clamp technique (at 37 degrees C). Incubation of atrial myocytes with 10 microg/mL LPS was found to significantly impair I(f) by suppressing the current at membrane potentials positive to -80 mV and slowing down current activation, but without effecting maximal current conductance. Furthermore, in incubated cells (10 microg/mL), the response of I(f) to [beta]-adrenergic stimulation (1 microM isoproterenol) was significantly larger compared with control cells (shift of half-maximal activation voltage to more positive potentials amounted to -10 and -14 mV in untreated and treated cells, respectively). Simulations using a spontaneously active sinoatrial cell model demonstrated that LPS-induced I(f) impairment reduced the responsiveness of the model cell to fluctuations of autonomic input. This study showed a direct impact of LPS on the cardiac pacemaker current I(f). The LPS-induced I(f) impairment may contribute to the clinically observed reduction in heart rate variability under septic conditions and in cardiac diseases such as heart failure, where endotoxin can be of pathophysiological relevance.
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December 2007

Oxidized LDL induces ventricular myocyte damage and abnormal electrical activity--role of lipid hydroperoxides.

Cardiovasc Res 2005 Apr 8;66(1):74-83. Epub 2005 Jan 8.

Center of Physiological Medicine, Institute of Biophysics, Medical University Graz, Harrachgasse 21/4, A-8010 Graz, Austria.

Objective: It was our aim to investigate effects of human LDL, copper-, or AAPH-oxidized over different periods of time to different degrees (ox-LDL), on viability and electrophysiological parameters of isolated ventricular myocytes of guinea pigs.

Methods: Guinea pig ventricular myocytes were incubated with ox-LDL or native LDL (at 0.5 mg/ml) for 12 h, and afterwards myocyte damage, action potentials, and transmembrane ion currents were studied (at 37 degrees C).

Results: Ox-LDL was found to induce severe myocyte damage, whereas native LDL had no effect. Myocyte damage was dependent on the content of total lipid hydroperoxides in both copper-oxidized and AAPH-oxidized LDL. Incubation with ox-LDL led to intense contractile and electrophysiological effects including prolongation of action potential duration, depolarization of resting membrane potential, spontaneous activity, generation of afterdepolarizations, and modification of transmembrane ion currents (e.g. inward rectifier, calcium, and background currents).

Conclusions: Ox-LDL induced cell damage and irregular electrical activity in ventricular myocytes. These effects were dependent on the lipid hydroperoxide content of ox-LDL and were similar to oxidative stress (OS) induced by various OS-generating systems. The observed effects may play a role for functional cardiac abnormalities in patients with increased ox-LDL levels.
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http://dx.doi.org/10.1016/j.cardiores.2004.12.009DOI Listing
April 2005

An ionic model for rhythmic activity in small clusters of embryonic chick ventricular cells.

Am J Physiol Heart Circ Physiol 2005 Jul 11;289(1):H398-413. Epub 2005 Feb 11.

Dept. of Physiology, McGill University, 3655 Sir William Osler Promenade, Montreal, Quebec H3G 1Y6, Canada.

We recorded transmembrane potential in whole cell recording mode from small clusters (2-4 cells) of spontaneously beating 7-day embryonic chick ventricular cells after 1-3 days in culture and investigated effects of the blockers D-600, diltiazem, almokalant, and Ba2+. Electrical activity in small clusters is very different from that in reaggregates of several hundred embryonic chick ventricular cells, e.g., TTX-sensitive fast upstrokes in reaggregates vs. TTX-insensitive slow upstrokes in small clusters (maximum upstroke velocity approximately 100 V/s vs. approximately 10 V/s). On the basis of our voltage- and current-clamp results and data from the literature, we formulated a Hodgkin-Huxley-type ionic model for the electrical activity in these small clusters. The model contains a Ca2+ current (ICa), three K+ currents (IKs, IKr, and IK1), a background current, and a seal-leak current. ICa generates the slow upstroke, whereas IKs, IKr, and IK1 contribute to repolarization. All the currents contribute to spontaneous diastolic depolarization, e.g., removal of the seal-leak current increases the interbeat interval from 392 to 535 ms. The model replicates the spontaneous activity in the clusters as well as the experimental results of application of blockers. Bifurcation analysis and simulations with the model predict that annihilation and single-pulse triggering should occur with partial block of ICa. Embryonic chick ventricular cells have been used as an experimental model to investigate various aspects of spontaneous beating of cardiac cells, e.g., mutual synchronization, regularity of beating, and spontaneous initiation and termination of reentrant rhythms; our model allows investigation of these topics through numerical simulation.
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http://dx.doi.org/10.1152/ajpheart.00683.2004DOI Listing
July 2005

If in left human atrium: a potential contributor to atrial ectopy.

Cardiovasc Res 2004 Nov;64(2):250-9

Institut für Medizinische Physik und Biophysik, Medizinische Universität Graz, Harrachgasse 21, A-8010 Graz, Austria.

Objective: The left human atrium plays an important role in initiation of atrial fibrillation (AF) and the hyperpolarization activated cation current (I(f)) is a candidate for contributing to abnormal automaticity. However, electrophysiological data concerning I(f) are not available in this cardiac region and we therefore investigated I(f) in human left atrial tissue.

Methods: Human atrial myocytes were isolated from the left atrial appendage (LAA) and the left atrial wall (LAW) obtained from patients undergoing open heart surgery. I(f) was measured with the whole-cell patch-clamp technique.

Results: I(f) densities between -70 and -110 mV were found to be significantly higher in LAA than in LAW cells. Furthermore, in the group of LAA cells the half maximal activation potential (V(1/2)) was found to be less negative (V(1/2) of -84.3+/-1.9 mV, n=14/9) compared to LAW cells (V(1/2) of -97.8+/-2.1 mV, n=28/9). Beta-adrenergic receptor stimulation with isoproterenol (1 microM) caused an acceleration of current activation and a V(1/2) shift to more positive potentials in cells of both regions (LAA: 8.8+/-2.3 mV, n=6/4 and LAW: 8.9+/-2.6 mV, n=6/4). Simulations using a mathematical model of the human atrial myocyte demonstrated that I(f) was able to induce spontaneous activity in the model at a regular rhythm due to the interplay of I(f), Na(+)/Ca(2+) exchange current and Ca(2+) release of the sarcoplasmic reticulum (SR).

Conclusions: Our study revealed the presence of I(f) in left atrial myocytes and showed that I(f) parameters depend on atrial region. I(f) current densities were sufficient to convert the mathematical model of a quiescent human atrial cell into a "pacemaker cell". These data support the hypothesis of I(f) as a contributor to abnormal automaticity in human atrial tissue.
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http://dx.doi.org/10.1016/j.cardiores.2004.07.001DOI Listing
November 2004

A hyperpolarization activated inward current (If) is present in infant ventricular myocytes.

Basic Res Cardiol 2003 Nov 16;98(6):362-6. Epub 2003 Jul 16.

Institut für Medizinische Physik und Biophysik, Universität Graz, Harrachgasse 21, 8010 Graz, Austria.

I(f) was shown to be present in adult human atrial and ventricular myocytes but data obtained from infant myocytes are lacking. We have studied I(f) in isolated ventricular myocytes from children undergoing surgical correction of tetralogy of Fallot (TOF; n = 5; mean age: 15.3 months). All recordings were made with the patch clamp technique in the whole cell mode at a temperature of 36-37 degrees C. A modified Tyrode solution containing 25 mM KCl was used to amplify I(f). Considering I(f) to be present when its current density at -120 mV was greater than 0.5 pA/pF, I(f) could be found in 28 out of 32 myocytes (88%). The mean current density was -2.01 +/- 0.3 pA/pF (mean +/- S.E.M.). First current activation occurred at -70 mV and I(f) could be reversibly inhibited by superfusing the myocytes with CsCl (2 mM). Half maximal activation (V(1/2)) of I(f) was at -80.3 +/- 1.0 mV (n = 28). Beta-adrenergic receptor stimulation with isoproterenol (1 microM) caused an acceleration of current activation and a shift of V(1/2) by 7.88 +/- 1.8 mV (n = 10) to less negative potentials. This study provides first evidence that the hyperpolarization-activated pacemaker current I(f) is present in infant human ventricular myocytes. Our results suggest that I(f) in ventricle of infants suffering from TOF has similar properties as I(f) in adult ventricle.
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http://dx.doi.org/10.1007/s00395-003-0424-9DOI Listing
November 2003

NADH supplementation decreases pinacidil-primed I K ATP in ventricular cardiomyocytes by increasing intracellular ATP.

Br J Pharmacol 2003 Jun;139(4):749-54

Institut für Medizinische Physik und Biophysik, Karl-Franzens-Universität Graz, Harrachgasse 21, A-8010 Graz, Austria.

1 The aim of this study was to investigate the effect of nicotinamide-adenine dinucleotide (NADH) supplementation on the metabolic condition of isolated guinea-pig ventricular cardiomyocytes. The pinacidil-primed ATP-dependent potassium current I(K(ATP)) was used as an indicator of subsarcolemmal ATP concentration and intracellular adenine nucleotide contents were measured. 2 Membrane currents were studied using the patch-clamp technique in the whole-cell recording mode at 36-37 degrees C. Adenine nucleotides were determined by HPLC. 3 Under physiological conditions (4.3 mM ATP in the pipette solution, ATP(i)) I(K(ATP)) did not contribute to basal electrical activity. 4 The ATP-dependent potassium (K((ATP))) channel opener pinacidil activated I(K(ATP)) dependent on [ATP](i) showing a significantly more pronounced activation at lower (1 mM) [ATP](i). 5 Supplementation of cardiomyocytes with 300 micro g ml(-1) NADH (4-6 h) resulted in a significantly reduced I(K(ATP)) activation by pinacidil compared to control cells. The current density was 13.8+/-3.78 (n=6) versus 28.9+/-3.38 pA pF(-1) (n=19; P<0.05). 6 Equimolar amounts of the related compounds nicotinamide and NAD(+) did not achieve a similar effect like NADH. 7 Measurement of adenine nucleotides by HPLC revealed a significant increase in intracellular ATP (NADH supplementation: 45.6+/-1.88 nmol mg(-1) protein versus control: 35.4+/-2.57 nmol mg(-1) protein, P<0.000005). 8 These data show that supplementation of guinea-pig ventricular cardiomyocytes with NADH results in a decreased activation of I(K(ATP)) by pinacidil compared to control myocytes, indicating a higher subsarcolemmal ATP concentration. 9 Analysis of intracellular adenine nucleotides by HPLC confirmed the significant increase in ATP.
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http://dx.doi.org/10.1038/sj.bjp.0705300DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1573896PMC
June 2003
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