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Milan HFM, Almazloum AA, Bassani RA, Bassani JWM. Membrane polarization at the excitation threshold induced by external electric fields in cardiomyocytes of rats at different developmental stages. Med Biol Eng Comput 2023; 61:2637-2647. [PMID: 37405671 DOI: 10.1007/s11517-023-02868-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2023] [Accepted: 06/07/2023] [Indexed: 07/06/2023]
Abstract
External electric fields (E), used for cardiac pacing and defibrillation/cardioversion, induce a spatially variable change in cardiomyocyte transmembrane potential (ΔVm) that depends on cell geometry and E orientation. This study investigates E-induced ΔVm in cardiomyocytes from rats at different ages, which show marked size/geometry variation. Using a tridimensional numerical electromagnetic model recently proposed (NM3D), it was possible: (a) to evaluate the suitability of the simpler, prolate spheroid analytical model (PSAM) to calculate amplitude and location of ΔVm maximum (ΔVmax) for E = 1 V.cm-1; and (b) to estimate the ΔVmax required for excitation (ΔVT) from experimentally determined threshold E values (ET). Ventricular myocytes were isolated from neonatal, weaning, adult, and aging Wistar rats. NM3D was constructed as the extruded 2D microscopy cell image, while measured minor and major cell dimensions were used for PSAM. Acceptable ΔVm estimates can be obtained with PSAM from paralelepidal cells for small θ. ET, but not ΔVT, was higher for neonate cells. ΔVT was significantly greater in the cell from older animals, which indicate lower responsiveness to E associated with aging, rather than with altered cell geometry/dimensions. ΔVT might be used as a non-invasive indicator of cell excitability as it is little affected by cell geometry/size.
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Affiliation(s)
- Hugo F M Milan
- Department of Electronics and Biomedical Engineering, School of Electrical and Computer Engineering, University of Campinas (UNICAMP), Cidade Universitária Zeferino Vaz, Av. Albert Einstein 400, Campinas, SP, 13083-852, Brazil.
| | - Ahmad A Almazloum
- Department of Electronics and Biomedical Engineering, School of Electrical and Computer Engineering, University of Campinas (UNICAMP), Cidade Universitária Zeferino Vaz, Av. Albert Einstein 400, Campinas, SP, 13083-852, Brazil
| | - Rosana A Bassani
- Department of Electronics and Biomedical Engineering, School of Electrical and Computer Engineering, University of Campinas (UNICAMP), Cidade Universitária Zeferino Vaz, Av. Albert Einstein 400, Campinas, SP, 13083-852, Brazil
- LabNECC, Center for Biomedical Engineering (CEB), University of Campinas (UNICAMP), R. Alexander Fleming 163, Cidade Universitária Zeferino Vaz, Campinas, SP, 13083-881, Brazil
| | - José W M Bassani
- Department of Electronics and Biomedical Engineering, School of Electrical and Computer Engineering, University of Campinas (UNICAMP), Cidade Universitária Zeferino Vaz, Av. Albert Einstein 400, Campinas, SP, 13083-852, Brazil
- LabNECC, Center for Biomedical Engineering (CEB), University of Campinas (UNICAMP), R. Alexander Fleming 163, Cidade Universitária Zeferino Vaz, Campinas, SP, 13083-881, Brazil
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Oshiyama NF, Pereira AHM, Cardoso AC, Franchini KG, Bassani JWM, Bassani RA. Developmental differences in myocardial transmembrane Na + transport: Implications for excitability and Na + handling. J Physiol 2022; 600:2651-2667. [PMID: 35489088 DOI: 10.1113/jp282661] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2021] [Accepted: 04/20/2022] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Previous studies showed that myocardial preparations from immature rats are less sensitive to electrical field stimulation than adult preparations. Freshly-isolated ventricular myocytes from neonatal rats showed lower excitability than adult cells, e.g., less negative threshold membrane potential and greater membrane depolarization required for action potential triggering. In addition to differences in mRNA levels for Na+ channels isoforms and greater Na+ current (INa ) density, Na+ channel voltage-dependence was shifted to the right in immature myocytes, which seems to be sufficient to decrease excitability, according to computer simulations. Only in neonatal myocytes did cyclic activity promote marked cytosolic Na+ accumulation, which was prevented by abolition of systolic Ca2+ transients by blockade of Ca2+ currents. Developmental changes in INa may account for the difference in action potential initiation parameters, but not for cytosolic Na+ accumulation, which seems to be due mainly to Na+ /Ca2+ exchanger-mediated Na+ influx. ABSTRACT Little is currently known about possible developmental changes in myocardial Na+ handling, which may have impact on cell excitability and Ca2+ content. Resting intracellular Na+ concentration ([Na+ ]i ), measured in freshly-isolated rat ventricular myocytes with CoroNa-green, was not significantly different in neonates (3-5 days old) and adults, but electrical stimulation caused marked [Na+ ]i rise only in neonates. Inhibition of L-type Ca2+ current by CdCl2 abolished not only systolic Ca2+ transients, but also activity-dependent intracellular Na+ accumulation in immature cells. This indicates that the main Na+ influx pathway during activity is the Na+ /Ca2+ exchanger, rather than voltage-dependent Na+ current (INa ), which was not affected by CdCl2 . In immature myocytes, INa density was 2-fold greater, inactivation was faster, and the current peak occurred at less negative transmembrane potential (Em ) than in adults. Na+ channel steady-state activation and inactivation curves in neonates showed a rightward shift, which should increase channel availability at diastolic Em , but also require greater depolarization for excitation, which was observed experimentally and reproduced in computer simulations. Ventricular mRNA levels of Nav 1.1, Nav 1.4 and Nav 1.5 pore-forming isoforms were greater in neonate ventricles, while decrease was seen for the β1 subunit. Both molecular and biophysical changes in the channel profile may contribute to the differences in INa density and voltage-dependence, and also to the less negative threshold Em in neonates, compared to adults. The apparently lower excitability in immature ventricle may confer protection against the development of spontaneous activity in this tissue. Abstract figure legend Little is currently known about possible developmental changes in myocardial Na+ transport, which may have impact on cell excitability and other physiological aspects. At the mRNA level, neonatal rat ventricle expresses a greater variety of Na+ channel isoforms than in adults. In immature ventricular cardiomyocytes, Na+ current (INa ) density was greater, but voltage-dependence is shifted to less negative potentials than in adults. This should increase channel availability at diastolic membrane potential, but also require greater depolarization for excitation, which was observed experimentally and reproduced in computer simulation. We also observed that electrical stimulation caused marked intracellular Na+ accumulation only in neonates, which was abolished when Ca2+ transients and the Na+ /Ca2+ exchanger (NCX) were inhibited by Cd2+ + Ni2+ . Thus, it seems that the main Na+ influx pathway during activity in neonates is the NCX, rather than voltage-dependent INa , which was not affected by these blockers. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Natália F Oshiyama
- Department of Biomedical Engineering, School of Electrical and Computer Engineering, University of Campinas, Campinas, SP, Brazil.,National Laboratory for Cell Calcium Study, (LabNECC), Center for Biomedical Engineering, University of Campinas, Campinas, SP, Brazil
| | - Ana H M Pereira
- Brazilian Biosciences National Laboratory, Brazilian Center for Research in Energy and Materials (LNBio/CNPEM), Campinas, SP, Brazil
| | - Alisson C Cardoso
- Brazilian Biosciences National Laboratory, Brazilian Center for Research in Energy and Materials (LNBio/CNPEM), Campinas, SP, Brazil
| | - Kleber G Franchini
- Brazilian Biosciences National Laboratory, Brazilian Center for Research in Energy and Materials (LNBio/CNPEM), Campinas, SP, Brazil.,Department of Internal Medicine, School of Medicine, University of Campinas, Campinas, SP, Brazil
| | - José W M Bassani
- Department of Biomedical Engineering, School of Electrical and Computer Engineering, University of Campinas, Campinas, SP, Brazil.,National Laboratory for Cell Calcium Study, (LabNECC), Center for Biomedical Engineering, University of Campinas, Campinas, SP, Brazil
| | - Rosana A Bassani
- Department of Biomedical Engineering, School of Electrical and Computer Engineering, University of Campinas, Campinas, SP, Brazil.,National Laboratory for Cell Calcium Study, (LabNECC), Center for Biomedical Engineering, University of Campinas, Campinas, SP, Brazil
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Zoccoler M, de Oliveira PX. METROID: an automated method for robust quantification of subcellular fluorescence events at low SNR. BMC Bioinformatics 2020; 21:332. [PMID: 32709217 PMCID: PMC7379836 DOI: 10.1186/s12859-020-03661-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2019] [Accepted: 07/14/2020] [Indexed: 11/23/2022] Open
Abstract
Background In cell biology, increasing focus has been directed to fast events at subcellular space with the advent of fluorescent probes. As an example, voltage sensitive dyes (VSD) have been used to measure membrane potentials. Yet, even the most recently developed genetically encoded voltage sensors have demanded exhausting signal averaging through repeated experiments to quantify action potentials (AP). This analysis may be further hampered in subcellular signals defined by small regions of interest (ROI), where signal-to-noise ratio (SNR) may fall substantially. Signal processing techniques like blind source separation (BSS) are designed to separate a multichannel mixture of signals into uncorrelated or independent sources, whose potential to separate ROI signal from noise has been poorly explored. Our aims are to develop a method capable of retrieving subcellular events with minimal a priori information from noisy cell fluorescence images and to provide it as a computational tool to be readily employed by the scientific community. Results In this paper, we have developed METROID (Morphological Extraction of Transmembrane potential from Regions Of Interest Device), a new computational tool to filter fluorescence signals from multiple ROIs, whose code and graphical interface are freely available. In this tool, we developed a new ROI definition procedure to automatically generate similar-area ROIs that follow cell shape. In addition, simulations and real data analysis were performed to recover AP and electroporation signals contaminated by noise by means of four types of BSS: Principal Component Analysis (PCA), Independent Component Analysis (ICA), and two versions with discrete wavelet transform (DWT). All these strategies allowed for signal extraction at low SNR (− 10 dB) without apparent signal distortion. Conclusions We demonstrate the great capability of our method to filter subcellular signals from noisy fluorescence images in a single trial, avoiding repeated experiments. We provide this novel biomedical application with a graphical user interface at 10.6084/m9.figshare.11344046.v1, and its code and datasets are available in GitHub at https://github.com/zoccoler/metroid.
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Affiliation(s)
- Marcelo Zoccoler
- Department of Biomedical Engineering (DEB), School of Electrical and Computer Engineering, University of Campinas, 400, Albert Einstein Avenue, Campinas, SP, 13083-852, Brazil.
| | - Pedro X de Oliveira
- Department of Biomedical Engineering (DEB), School of Electrical and Computer Engineering, University of Campinas, 400, Albert Einstein Avenue, Campinas, SP, 13083-852, Brazil.,Center for Biomedical Engineering (CEB), University of Campinas, Campinas, SP, Brazil
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Accuracy of electromagnetic models to estimate cardiomyocyte membrane polarization. Med Biol Eng Comput 2019; 57:2617-2627. [PMID: 31667705 DOI: 10.1007/s11517-019-02054-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Accepted: 09/27/2019] [Indexed: 10/25/2022]
Abstract
External electric fields (E) induce a spatially heterogeneous variation in the membrane potential (ΔVm) of cardiomyocytes that, if sufficiently large, results in an action potential and contraction. Insights into the phenomenon of ΔVm induction by E have been classically gained with electromagnetic models due to the lack of adequate experimental approaches. However, it is not clear yet how reliable these models are. To assess the accuracy of commonly used models, a reference 3D numerical model for cardiomyocytes (NMReal) was developed, consisting of the cell membrane shell reconstructed from rendered confocal microscopy images of freshly isolated ventricular myocytes. NMReal was used to estimate the E-induced maximum ΔVm values (ΔVmax), which were compared with estimates from seven other electromagnetic models. Accurate ΔVmax estimates (average error < 2%) were obtained with a less complex 3D model (NM3D) based on the extruded 2D image of the cell longitudinal section. Acceptable ΔVmax estimates (average error < 5%) were obtained with the prolate spheroid analytical model (PSAM) when the angle of E incidence and the cell major axis was < 30°. In this case, PSAM, a much simpler model requiring only the measurement of the longitudinal and transversal cell dimensions, can be a suitable alternative for ΔVmax calculation. Graphical abstract (A) Confocal images of the cell were used to reconstruct the realistic geometry of cardiomyocytes (NMReal). (B) NMReal was used to estimate the maximum variation in the transmembrane potential (ΔVmax) induced by an external electric field (E) applied at different angles with respect to the cell major axis. Plus (anode) and minus (cathode) signs indicate electrode position (E direction is from minus to plus). (C) Relative error (vs. NMReal) of ΔVmax estimation with simplified electromagnetic models, presented in descending order of accuracy (left-to-right, top-to-bottom). NM2D: 2D numerical model based on the longitudinal cell image; NM3D: numerical model based on the z extrusion of NM2D; EAM, PSAM, and CAM: ellipsoidal, prolate spheroidal, and cylindrical analytical models, respectively; PNM and CNM: parallelepipedal and cylindrical numerical models, respectively.
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Wilson MA, Liberzon I, Lindsey ML, Lokshina Y, Risbrough VB, Sah R, Wood SK, Williamson JB, Spinale FG. Common pathways and communication between the brain and heart: connecting post-traumatic stress disorder and heart failure. Stress 2019; 22:530-547. [PMID: 31161843 PMCID: PMC6690762 DOI: 10.1080/10253890.2019.1621283] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Psychiatric illnesses and cardiovascular disease (CVD) contribute to significant overall morbidity, mortality, and health care costs, and are predicted to reach epidemic proportions with the aging population. Within the Veterans Administration (VA) health care system, psychiatric illnesses such as post-traumatic stress disorder (PTSD) and CVD such as heart failure (HF), are leading causes of hospital admissions, prolonged hospital stays, and resource utilization. Numerous studies have demonstrated associations between PTSD symptoms and CVD endpoints, particularly in the Veteran population. Not only does PTSD increase the risk of HF, but this relationship is bi-directional. Accordingly, a VA-sponsored conference entitled "Cardiovascular Comorbidities in PTSD: The Brain-Heart Consortium" was convened to explore potential relationships and common biological pathways between PTSD and HF. The conference was framed around the hypothesis that specific common systems are dysregulated in both PTSD and HF, resulting in a synergistic acceleration and amplification of both disease processes. The conference was not intended to identify all independent pathways that give rise to PTSD and HF, but rather identify shared systems, pathways, and biological mediators that would be modifiable in both disease processes. The results from this conference identified specific endocrine, autonomic, immune, structural, genetic, and physiological changes that may contribute to shared PTSD-CVD pathophysiology and could represent unique opportunities to develop therapies for both PTSD and HF. Some recommendations from the group for future research opportunities are provided.
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Affiliation(s)
- Marlene A. Wilson
- Department of Pharmacology, Physiology and Neuroscience, University of South Carolina School of Medicine and Research Service, Columbia VA Health Care System, Columbia SC
- Corresponding author information: Marlene A. Wilson, Department of Pharmacology, Physiology and Neuroscience, University of South Carolina School of Medicine, Columbia SC 29208, Research Service, Columbia VA Health Care System, Columbia SC 29209, ; 803-216-3507
| | - Israel Liberzon
- Department of Psychiatry, Texas A&M College of Medicine, Bryan, TX
| | - Merry L. Lindsey
- Department of Cellular and Integrative Physiology, University of Nebraska Medical Center, and Research Service, Omaha VA Medical Center, Omaha NE
| | - Yana Lokshina
- Department of Psychiatry, Texas A&M College of Medicine, Bryan, TX
| | - Victoria B. Risbrough
- VA Center of Excellence for Stress and Mental Health, La Jolla CA, Dept. of Psychiatry, University of California San Diego
| | - Renu Sah
- Department of Pharmacology and Systems Physiology, University of Cincinnati College of Medicine, Cincinnati, OH
| | - Susan K. Wood
- Department of Pharmacology, Physiology and Neuroscience, University of South Carolina School of Medicine and Research Service, Columbia VA Health Care System, Columbia SC
| | - John B. Williamson
- Department of Neurology, University of Florida College of Medicine, Gainesville FL
| | - Francis G. Spinale
- Department of Cell Biology and Anatomy, University of South Carolina School of Medicine and Research Service, Columbia VA Health Care System., Columbia SC
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de Freitas JANLF, Dos Santos Costa Leomil F, Zoccoler M, Antoneli PC, de Oliveira PX. Cardiomyocyte lethality by multidirectional stimuli. Med Biol Eng Comput 2018; 56:2177-2184. [PMID: 29845489 DOI: 10.1007/s11517-018-1848-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2018] [Accepted: 05/16/2018] [Indexed: 10/16/2022]
Abstract
Multidirectional defibrillation protocols have shown better efficiency than monodirectional; still, no testing was performed to assess cell lethality. We investigated lethality of multidirectional defibrillator-like shocks on isolated cardiomyocytes. Cells were isolated from adult male Wistar rats and plated into a perfusion chamber. Electrical field stimulation threshold (ET) was obtained, and cells were paced with suprathreshold bipolar electrical field (E) pulses. Either one monodirectional high-intensity electrical field (HEF) pulse aligned at 0° (group Mono0) or 60° (group Mono60) to cell major axis or a multidirectional sequence of three HEF pulses aligned at 0°, 60°, and 120° each was applied. If cell recovered from shock, pacing was resumed, and a higher amplitude HEF, proportional to ET, was applied. The sequence was repeated until cell death. Lethality curves were built by means of survival analysis from sub-lethal and lethal E. Non-linear fit was performed, and E values corresponding to 50% probability of lethality (E50) were compared. Multidirectional groups presented lethality curves similar to Mono0. Mono60 displayed the highest E50. The novel data endorse the idea of multidirectional stimuli being safer because their effects on lethality of individual cells were equal to a single monodirectional stimulus, while their defibrillatory threshold is lower. Graphical abstract Monodirectional and multidirectional lethality protocol comparison on isolated rat cardiomyocytes. The heart image is a derivative of "3D Heart in zBrush" ( https://vimeo.com/65568770 ) by Laloxl, used under CC BY 3.0 ( https://creativecommons.org/licenses/by/3.0/legalcode )/image extracted from original video.
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Affiliation(s)
| | | | - Marcelo Zoccoler
- Department of Biomedical Engineering, School of Electrical and Computer Engineering, University of Campinas, São Paulo, Brazil.
| | - Priscila Correia Antoneli
- Department of Biomedical Engineering, School of Electrical and Computer Engineering, University of Campinas, São Paulo, Brazil
| | - Pedro Xavier de Oliveira
- Department of Biomedical Engineering, School of Electrical and Computer Engineering, University of Campinas, São Paulo, Brazil.,Center for Biomedical Engineering, University of Campinas, Campinas, São Paulo, Brazil
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Role of Beta-adrenergic Receptors and Sirtuin Signaling in the Heart During Aging, Heart Failure, and Adaptation to Stress. Cell Mol Neurobiol 2017; 38:109-120. [DOI: 10.1007/s10571-017-0557-2] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2017] [Accepted: 10/06/2017] [Indexed: 01/03/2023]
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Goulart JT, Bassani RA, Bassani JWM. Application based on the Canny edge detection algorithm for recording contractions of isolated cardiac myocytes. Comput Biol Med 2017; 81:106-110. [DOI: 10.1016/j.compbiomed.2016.12.014] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2016] [Revised: 12/11/2016] [Accepted: 12/20/2016] [Indexed: 10/20/2022]
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Toll-like receptor 4 activation promotes cardiac arrhythmias by decreasing the transient outward potassium current (Ito) through an IRF3-dependent and MyD88-independent pathway. J Mol Cell Cardiol 2014; 76:116-25. [PMID: 25169970 DOI: 10.1016/j.yjmcc.2014.08.012] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/23/2014] [Revised: 07/31/2014] [Accepted: 08/15/2014] [Indexed: 11/21/2022]
Abstract
Cardiac arrhythmias are one of the main causes of death worldwide. Several studies have shown that inflammation plays a key role in different cardiac diseases and Toll-like receptors (TLRs) seem to be involved in cardiac complications. In the present study, we investigated whether the activation of TLR4 induces cardiac electrical remodeling and arrhythmias, and the signaling pathway involved in these effects. Membrane potential was recorded in Wistar rat ventricle. Ca(2+) transients, as well as the L-type Ca(2+) current (ICaL) and the transient outward K(+) current (Ito), were recorded in isolated myocytes after 24 h exposure to the TLR4 agonist, lipopolysaccharide (LPS, 1 μg/ml). TLR4 stimulation in vitro promoted a cardiac electrical remodeling that leads to action potential prolongation associated with arrhythmic events, such as delayed afterdepolarization and triggered activity. After 24 h LPS incubation, Ito amplitude, as well as Kv4.3 and KChIP2 mRNA levels were reduced. The Ito decrease by LPS was prevented by inhibition of interferon regulatory factor 3 (IRF3), but not by inhibition of interleukin-1 receptor-associated kinase 4 (IRAK4) or nuclear factor kappa B (NF-κB). Extrasystolic activity was present in 25% of the cells, but apart from that, Ca(2+) transients and ICaL were not affected by LPS; however, Na(+)/Ca(2+) exchanger (NCX) activity was apparently increased. We conclude that TLR4 activation decreased Ito, which increased AP duration via a MyD88-independent, IRF3-dependent pathway. The longer action potential, associated with enhanced Ca(2+) efflux via NCX, could explain the presence of arrhythmias in the LPS group.
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Zafalon N, Oshiyama NF, Bassani JWM, Bassani RA. Muscarinic stimulation and pinacidil produce similar facilitation of tachyarrhythmia induction in rat isolated atria. J Mol Cell Cardiol 2013; 65:120-6. [PMID: 24140800 DOI: 10.1016/j.yjmcc.2013.10.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/13/2013] [Accepted: 10/09/2013] [Indexed: 10/26/2022]
Abstract
Atrial tachyarrhythmias, the most common type of cardiac arrhythmias, are associated with greater stroke risk. Muscarinic cholinergic agonists have been shown to facilitate atrial tachyarrhythmia maintenance in the absence of cardiac disease. This has been attributed to action potential shortening, which enhances myocardial electrical anisotropy, and thus creates a substrate for reentrant excitation. In this study, we describe a similar effect of the ATP-sensitive K(+) channel (KATP) opener pinacidil on tachyarrhythmia induction in isolated rat atria. Pinacidil, which activates a weakly inwardly-rectifying current in isolated atrial myocytes, enhanced arrhythmia induction in the right and left atria. This effect was abolished by the KATP blocker glibenclamide, but not by atropine, which rules out a possible indirect effect due to stimulation of acetylcholine release. However, pinacidil attenuated carbachol-induced tachyarrhythmia facilitation, which may indicate that the action of these agonists converges to a common cellular mechanism. Both agonists caused marked action potential shortening in isolated atrial myocytes. Moreover, during arrhythmia in the presence of pinacidil and carbachol, the atrial vectorelectrographic patterns were similar and consistent with reentrant propagation of the electrical activity. From these results, we conclude that the KATP channel opening is pro-arrhythmic in atrial tissue, which may pose as an additional risk in the scenario of myocardial hypoxia. Moreover, the similarity of the electrophysiological effects of pinacidil and carbachol is suggestive that the sole increase in background K(+) conductance is sufficient for atrial tachyarrhythmia facilitation.
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Affiliation(s)
- Nivaldo Zafalon
- Department of Biomedical Engineering/FEEC, University of Campinas, Caixa Postal 6040, 13084-971 Campinas, SP, Brazil.
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Fonseca AVS, Bassani RA, Oliveira PX, Bassani JWM. Greater Cardiac Cell Excitation Efficiency With Rapidly Switching Multidirectional Electrical Stimulation. IEEE Trans Biomed Eng 2013; 60:28-34. [DOI: 10.1109/tbme.2012.2220766] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Boer DC, Bassani JWM, Bassani RA. Functional antagonism of β-adrenoceptor subtypes in the catecholamine-induced automatism in rat myocardium. Br J Pharmacol 2011; 162:1314-25. [PMID: 21091648 DOI: 10.1111/j.1476-5381.2010.01121.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
BACKGROUND AND PURPOSE Myocardial automatism and arrhythmias may ensue during strong sympathetic stimulation. We sought to investigate the relevant types of adrenoceptor, as well as the role of phosphodiesterase (PDE) activity, in the production of catecholaminergic automatism in atrial and ventricular rat myocardium. EXPERIMENTAL APPROACH The effects of adrenoceptor agonists on the rate of spontaneous contractions (automatic response) and the amplitude of electrically evoked contractions (inotropic response) were determined in left atria and ventricular myocytes isolated from Wistar rats. KEY RESULTS Catecholaminergic automatism was Ca(2+) -dependent, as it required a functional sarcoplasmic reticulum to be exhibited. Although both α- and β-adrenoceptor activation caused inotropic stimulation, only β(1) -adrenoceptors seemed to mediate the induction of spontaneous activity. Catecholaminergic automatism was enhanced and suppressed by β(2) -adrenoceptor blockade and stimulation respectively. Inhibition of either PDE3 or PDE4 (by milrinone and rolipram, respectively) potentiated the automatic response of myocytes to catecholamines. However, only rolipram abolished the attenuation of automatism produced by β(2) -adrenoceptor stimulation. CONCLUSIONS AND IMPLICATIONS α- and β(2) -adrenoceptors do not seem to be involved in the mediation of catecholaminergic stimulation of spontaneous activity in atrial and ventricular myocardium. However, a functional antagonism of β(1) - and β(2) -adrenoceptor activation was identified, the former mediating catecholaminergic myocardial automatism and the latter attenuating this effect. Results suggest that hydrolysis of cAMP by PDE4 is involved in the protective effect mediated by β(2) -adrenoceptor stimulation.
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Affiliation(s)
- D C Boer
- Center for Biomedical Engineering, and Department of Biomedical Engineering, School of Electrical and Computer Engineering, University of Campinas, Campinas, SP, Brazil
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