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Clark RB, Giles WR. Current-Voltage Relationship for Late Na(+) Current in Adult Rat Ventricular Myocytes. CURRENT TOPICS IN MEMBRANES 2016; 78:451-78. [PMID: 27586292 DOI: 10.1016/bs.ctm.2016.04.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
It is now well established that the slowly inactivating component of the Na(+) current (INa-L) in the mammalian heart is a significant regulator of the action potential waveform. This insight has led to detailed studies of the role of INa-L in a number of important and challenging pathophysiological settings. These include genetically based ventricular arrhythmias (LQT 1, 2, and 3), ventricular arrhythmias arising from progressive cardiomyopathies (including diabetic), and proarrhythmic abnormalities that develop during local or global ventricular ischemia. Inhibition of INa-L may also be a useful strategy for management of atrial flutter and fibrillation. Many important biophysical parameters that characterize INa-L have been identified; and INa-L as an antiarrhythmia drug target has been studied extensively. However, relatively little information is available regarding (1) the ion transfer or current-voltage relationship for INa-L or (2) the time course of its reactivation at membrane potentials similar to the resting or diastolic membrane potential in mammalian ventricle. This chapter is based on our preliminary findings concerning these two very important physiological/biophysical descriptors for INa-L. Our results were obtained using whole-cell voltage clamp methods applied to enzymatically isolated rat ventricular myocytes. A chemical agent, BDF 9148, which was once considered to be a drug candidate in the Na(+)-dependent inotropic agent category has been used to markedly enhance INa-L current. BDF acts in a potent, selective, and reversible fashion. These BDF 9148 effects are compared and contrasted with the prototypical activator of INa-L, a sea anemone toxin, ATX II.
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Affiliation(s)
- R B Clark
- University of Calgary, Calgary, AB, Canada
| | - W R Giles
- University of Calgary, Calgary, AB, Canada
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Hou JW, Li W, Guo K, Chen XM, Chen YH, Li CY, Zhao BC, Zhao J, Wang H, Wang YP, Li YG. Antiarrhythmic effects and potential mechanism of WenXin KeLi in cardiac Purkinje cells. Heart Rhythm 2016; 13:973-82. [DOI: 10.1016/j.hrthm.2015.12.023] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/25/2015] [Indexed: 10/22/2022]
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Maass K, Shekhar A, Lu J, Kang G, See F, Kim EE, Delgado C, Shen S, Cohen L, Fishman GI. Isolation and characterization of embryonic stem cell-derived cardiac Purkinje cells. Stem Cells 2016; 33:1102-12. [PMID: 25524238 DOI: 10.1002/stem.1921] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2014] [Revised: 11/18/2014] [Accepted: 11/18/2014] [Indexed: 12/16/2022]
Abstract
The cardiac Purkinje fiber network is composed of highly specialized cardiomyocytes responsible for the synchronous excitation and contraction of the ventricles. Computational modeling, experimental animal studies, and intracardiac electrical recordings from patients with heritable and acquired forms of heart disease suggest that Purkinje cells (PCs) may also serve as critical triggers of life-threatening arrhythmias. Nonetheless, owing to the difficulty in isolating and studying this rare population of cells, the precise role of PC in arrhythmogenesis and the underlying molecular mechanisms responsible for their proarrhythmic behavior are not fully characterized. Conceptually, a stem cell-based model system might facilitate studies of PC-dependent arrhythmia mechanisms and serve as a platform to test novel therapeutics. Here, we describe the generation of murine embryonic stem cells (ESC) harboring pan-cardiomyocyte and PC-specific reporter genes. We demonstrate that the dual reporter gene strategy may be used to identify and isolate the rare ESC-derived PC (ESC-PC) from a mixed population of cardiogenic cells. ESC-PC display transcriptional signatures and functional properties, including action potentials, intracellular calcium cycling, and chronotropic behavior comparable to endogenous PC. Our results suggest that stem-cell derived PC are a feasible new platform for studies of developmental biology, disease pathogenesis, and screening for novel antiarrhythmic therapies.
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Affiliation(s)
- Karen Maass
- Leon H. Charney Division of Cardiology, New York University School of Medicine, New York, New York, USA
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Abstract
An electrophysiological analysis of canine single ventricular myocardial (VM) and Purkinje (P) cells was carried out by means of whole cell voltage clamp method. The following results in VM versus P cells were obtained. INa3 was present, had a threshold negative to the fast activating-inactivating INa1, its slow inactivation was cut off by INa1, and contributed to Na+ influx at INa1 threshold. INa1 was smaller and had a less negative threshold. There was no comparable slowly inactivating INa2, accounting for the shorter action potential. Slope conductance at resting potential was about double and decreased to a minimum value at the larger and less negative IK1 peak. The negative slope region of I-V relation was smaller during fast ramps and larger during slow ramps than in P cells, occurred in the voltage range of IK1 block by Mg2+, was not affected by a lower Vh and TTX and was eliminated by Ba2+, in contrast to P cells. ICa was larger, peaked at positive potentials and was eliminated by Ni2+. Ito was much smaller, began at more positive values, was abolished by less negative Vh and by 4-aminopyridine, included a sustained current that 4-aminopyridine decreased but did not eliminate. Steeper ramps increased IK1 peak as well as the fall in outward current during repolarization, consistent with a time-dependent block and unblock of IK1 by polyamines. During repolarization, the positive slope region was consistently present and was similar in amplitude to IK1 peak, whereas it was small or altogether missing in P cells. The total outward current at positive potentials comprised a larger IK1 component whereas it included a larger Ito and sustained current in P cells. These and other results provide a better understanding of the mechanisms underlying the action potential of VM and P cells under normal and some abnormal (arrhythmias) conditions.
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Affiliation(s)
- M Vassalle
- Department of Physiology and Pharmacology, State University of New York, Downstate Medical Center, 450 Clarkson Avenue, Brooklyn, NY 11203, U.S.A
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Affiliation(s)
- Antonio Zaza
- Dipartimento di Biotecnologie e Bioscienze, Università degli Studi Milano-Bicocca, Milano, Italy,
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6
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Cavanaugh J, French JA. Post-partum variation in the expression of paternal care is unrelated to urinary steroid metabolites in marmoset fathers. Horm Behav 2013; 63:551-8. [PMID: 23439223 PMCID: PMC3746002 DOI: 10.1016/j.yhbeh.2013.02.006] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/19/2012] [Revised: 02/11/2013] [Accepted: 02/12/2013] [Indexed: 11/17/2022]
Abstract
The organization and activation of maternal care are known to be highly regulated by hormones and there is growing evidence that expression of paternal care is also related to endocrine substrates. We examined the relationship between paternal behavior and steroid hormones in marmoset fathers (Callithrix geoffroyi) and evaluated whether hormone-paternal behavior relationships were altered by previous offspring-care experience in males. Based on previous findings, we predicted that testosterone, estradiol, and cortisol would decrease following the birth of offspring and would be lowest during the period of maximal infant carrying. Furthermore, we predicted that post-partum changes in carrying effort and hormone levels would be influenced by the level of offspring-care experience. Carrying effort and other paternal care behaviors underwent temporal changes over the post-partum period, but these patterns were not related to variation in hormone concentrations over the same period. There was a limited effect of offspring-care experience on hormone concentrations, but experience was found to play a role in the expression of paternal care, with experienced fathers engaging in significantly more infant allogrooming than inexperienced fathers. Furthermore, inexperienced fathers increased the frequency of food sharing in response to infant begging across the post-partum period, while experienced fathers displayed consistently low levels. We posit that a combination of experiential factors and an increased role for alloparents in offspring-care led to these changes. However, it appears that hormonal changes may not influence paternal responsiveness in white-faced marmoset fathers and that hormone-paternal behavior relationships are not critically dependent on a male's previous offspring-care experience.
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Affiliation(s)
- Jon Cavanaugh
- Callitrichid Research Center, Department of Psychology, University of Nebraska, Omaha, NE 68182, USA.
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Vaidyanathan R, O'Connell RP, Deo M, Milstein ML, Furspan P, Herron TJ, Pandit SV, Musa H, Berenfeld O, Jalife J, Anumonwo JMB. The ionic bases of the action potential in isolated mouse cardiac Purkinje cell. Heart Rhythm 2012; 10:80-7. [PMID: 23041576 DOI: 10.1016/j.hrthm.2012.10.002] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/18/2012] [Indexed: 02/01/2023]
Abstract
BACKGROUND Collecting electrophysiological and molecular data from the murine conduction system presents technical challenges. Thus, only little advantage has been taken of numerous genetically engineered murine models to study excitation through the cardiac conduction system of the mouse. OBJECTIVE To develop an approach for isolating murine cardiac Purkinje cells (PCs), to characterize major ionic currents and to use the data to simulate action potentials (APs) recorded from PCs. METHODS Light microscopy was used to isolate and identify PCs from apical and septal cells. Current and voltage clamp techniques were used to record APs and whole cell currents. We then simulated a PC AP on the basis of our experimental data. RESULTS APs recorded from PCs were significantly longer than those recorded from ventricular cells. The prominent plateau phase of the PC AP was very negative (≈-40 mV). Spontaneous activity was observed only in PCs. The inward rectifier current demonstrated no significant differences compared to ventricular myocytes (VMs). However, sodium current density was larger, and the voltage-gated potassium current density was significantly less in PCs compared with myocytes. T-type Ca(2+) currents (I(Ca,T)) were present in PCs but not VMs. Computer simulations suggest that I(Ca,T) and cytosolic calcium diffusion significantly modulate AP profile recorded in PCs, as compared to VMs. CONCLUSIONS Our study provides the first comprehensive ionic profile of murine PCs. The data show unique features of PC ionic mechanisms that govern its excitation process. Experimental data and numerical modeling results suggest that a smaller voltage-gated potassium current and the presence of I(Ca,T) are important determinants of the longer and relatively negative plateau phase of the APs.
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Affiliation(s)
- Ravi Vaidyanathan
- Department of Pharmacology, SUNY Upstate Medical University, Syracuse, New York, USA
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Moreno JD, Clancy CE. Pathophysiology of the cardiac late Na current and its potential as a drug target. J Mol Cell Cardiol 2011; 52:608-19. [PMID: 22198344 DOI: 10.1016/j.yjmcc.2011.12.003] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/02/2011] [Revised: 11/30/2011] [Accepted: 12/07/2011] [Indexed: 12/19/2022]
Abstract
A pathological increase in the late component of the cardiac Na(+) current, I(NaL), has been linked to disease manifestation in inherited and acquired cardiac diseases including the long QT variant 3 (LQT3) syndrome and heart failure. Disruption in I(NaL) leads to action potential prolongation, disruption of normal cellular repolarization, development of arrhythmia triggers, and propensity to ventricular arrhythmia. Attempts to treat arrhythmogenic sequelae from inherited and acquired syndromes pharmacologically with common Na(+) channel blockers (e.g. flecainide, lidocaine, and amiodarone) have been largely unsuccessful. This is due to drug toxicity and the failure of most current drugs to discriminate between the peak current component, chiefly responsible for single cell excitability and propagation in coupled tissue, and the late component (I(NaL)) of the Na(+) current. Although small in magnitude as compared to the peak Na(+) current (~1-3%), I(NaL) alters action potential properties and increases Na(+) loading in cardiac cells. With the increasing recognition that multiple cardiac pathological conditions share phenotypic manifestations of I(NaL) upregulation, there has been renewed interest in specific pharmacological inhibition of I(Na). The novel antianginal agent ranolazine, which shows a marked selectivity for late versus peak Na(+) current, may represent a novel drug archetype for targeted reduction of I(NaL). This article aims to review common pathophysiological mechanisms leading to enhanced I(NaL) in LQT3 and heart failure as prototypical disease conditions. Also reviewed are promising therapeutic strategies tailored to alter the molecular mechanisms underlying I(Na) mediated arrhythmia triggers.
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Affiliation(s)
- Jonathan D Moreno
- Tri-Institutional MD-PhD Program, Weill Cornell Medical College/The Rockefeller University/Sloan-Kettering Cancer Institute, New York, NY 10021, USA
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Sampson KJ, Iyer V, Marks AR, Kass RS. A computational model of Purkinje fibre single cell electrophysiology: implications for the long QT syndrome. J Physiol 2010; 588:2643-55. [PMID: 20498233 DOI: 10.1113/jphysiol.2010.187328] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Computer modelling has emerged as a particularly useful tool in understanding the physiology and pathophysiology of cardiac tissues. Models of ventricular, atrial and nodal tissue have evolved and include detailed ion channel kinetics and intercellular Ca(2+) handling. Purkinje fibre cells play a central role in the electrophysiology of the heart and in the genesis of cardiac arrhythmias. In this study, a new computational model has been constructed that incorporates the major membrane currents that have been isolated in recent experiments using Purkinje fibre cells. The model, which integrates mathematical models of human ion channels based on detailed biophysical studies of their kinetic and voltage-dependent properties, recapitulates distinct electrophysiological characteristics unique to Purkinje fibre cells compared to neighbouring ventricular myocytes. These characteristics include automaticity, hyperpolarized voltage range of the action potential plateau potential, and prolonged action potential duration. Simulations of selective ion channel blockade reproduce responses to pharmacological challenges characteristic of isolated Purkinje fibres in vitro, and importantly, the model predicts that Purkinje fibre cells are prone to severe arrhythmogenic activity in patients harbouring long QT syndrome 3 but much less so for other common forms of long QT. This new Purkinje cellular model can be a useful tool to study tissue-specific drug interactions and the effects of disease-related ion channel dysfunction on the cardiac conduction system.
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Affiliation(s)
- K J Sampson
- Department of Pharmacology, College of Physicians and Surgeons of Columbia University, New York, NY 10032, USA
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Aslanidi OV, Stewart P, Boyett MR, Zhang H. Optimal velocity and safety of discontinuous conduction through the heterogeneous Purkinje-ventricular junction. Biophys J 2009; 97:20-39. [PMID: 19580741 DOI: 10.1016/j.bpj.2009.03.061] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2008] [Revised: 02/20/2009] [Accepted: 03/27/2009] [Indexed: 11/19/2022] Open
Abstract
Slow and discontinuous wave conduction through nonuniform junctions in cardiac tissues is generally considered unsafe and proarrythmogenic. However, the relationships between tissue structure, wave conduction velocity, and safety at such junctions are unknown. We have developed a structurally and electrophysiologically detailed model of the canine Purkinje-ventricular junction (PVJ) and varied its heterogeneity parameters to determine such relationships. We show that neither very fast nor very slow conduction is safe, and there exists an optimal velocity that provides the maximum safety factor for conduction through the junction. The resultant conduction time delay across the PVJ is a natural consequence of the electrophysiological and morphological differences between the Purkinje fiber and ventricular tissue. The delay allows the PVJ to accumulate and pass sufficient charge to excite the adjacent ventricular tissue, but is not long enough for the source-to-load mismatch at the junction to be enhanced over time. The observed relationships between the conduction velocity and safety factor can provide new insights into optimal conditions for wave propagation through nonuniform junctions between various cardiac tissues.
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Affiliation(s)
- Oleg V Aslanidi
- Biological Physics Group, School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom
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Use-dependent block of cardiac late Na(+) current by ranolazine. Heart Rhythm 2009; 6:1625-31. [PMID: 19879541 DOI: 10.1016/j.hrthm.2009.07.042] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/28/2009] [Accepted: 07/20/2009] [Indexed: 12/19/2022]
Abstract
BACKGROUND Ranolazine is an antianginal drug that inhibits the cardiac late Na+ current (INa). The selectivity of ranolazine to block late INa relative to peak INa at rapid heart rates has not been determined, but is potentially important to drug efficacy and safety. OBJECTIVE This study sought to quantify use-dependent block (UDB) of cardiac peak and late INa by ranolazine. METHODS Wild-type (WT) and long QT3 mutation R1623Q channels were expressed in HEK293 cells and studied using whole-cell patch-clamp technique. RESULTS Ranolazine (1 to 300 microM caused tonic (0.1 Hz) and UDB (1, 2, and 5 Hz) of WT and R1623Q peak INa. The IC50 values for block of WT and R1623Q peak INa at 0.1, 1, 2, and 5 Hz were 430, 260, 157, and 154 microM, and 95, 77, 37, and 25 microM, respectively. The IC50 values for block of R1623Q late INa at 0.1, 1, 2, and 5 Hz were 7.5, 7.3, 2.2, and 1.9 microM, respectively. Ranolazine (10 microM) caused a hyperpolarizing shift of WT and R1623Q peak INa steady-state inactivation without affecting steady-state activation, suggesting that ranolazine interacts with inactivated states of the channels. Ranolazine (30 microM) significantly slowed the recovery from inactivation of peak INa of both WT and R1623Q and late INa of R1623Q. CONCLUSION Ranolazine slowed recovery of late INa from inactivation and thus caused UDB of late INa. These data suggest that the effect of ranolazine to block late INa may be increased and the selectivity to block late INa relative to peak INa may be retained during tachycardia.
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Maltsev VA, Kyle JW, Undrovinas A. Late Na+ current produced by human cardiac Na+ channel isoform Nav1.5 is modulated by its beta1 subunit. J Physiol Sci 2009; 59:217-25. [PMID: 19340536 PMCID: PMC2744134 DOI: 10.1007/s12576-009-0029-7] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2008] [Accepted: 02/02/2009] [Indexed: 01/26/2023]
Abstract
Experimental data accumulated over the past decade show the emerging importance of the late sodium current (I(NaL)) for the function of both normal and, especially, failing myocardium, in which I(NaL) is reportedly increased. While recent molecular studies identified the cardiac Na(+) channel (NaCh) alpha subunit isoform (Na(v)1.5) as a major contributor to I (NaL), the molecular mechanisms underlying alterations of I(NaL) in heart failure (HF) are still unknown. Here we tested the hypothesis that I(NaL) is modulated by the NaCh auxiliary beta subunits. tsA201 cells were transfected simultaneously with human Na(v)1.5 (former hH1a) and cardiac beta(1) or beta(2) subunits, and whole-cell patch-clamp experiments were performed. We found that I(NaL) decay kinetics were significantly slower in cells expressing alpha + beta(1) (time constant tau = 0.73 +/- 0.16 s, n = 14, mean +/- SEM, P < 0.05) but remained unchanged in cells expressing alpha + beta(2) (tau = 0.52 +/- 0.09 s, n = 5), compared with cells expressing Na(v)1.5 alone (tau = 0.54 +/- 0.09 s, n = 20). Also, beta(1), but not beta(2), dramatically increased I(NaL) relative to the maximum peak current, I(NaT) (2.3 +/- 0.48%, n = 14 vs. 0.48 +/- 0.07%, n = 6, P < 0.05, respectively) and produced a rightward shift of the steady-state availability curve. We conclude that the auxiliary beta(1) subunit modulates I(NaL), produced by the human cardiac Na(+) channel Na(v)1.5 by slowing its decay and increasing I(NaL) amplitude relative to I(NaT). Because expression of Na(v)1.5 reportedly decreases but beta(1) remains unchanged in chronic HF, the relatively higher expression of beta(1) may contribute to the known I(NaL) increase in HF via the modulation mechanism found in this study.
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Affiliation(s)
- Victor A. Maltsev
- Department of Internal Medicine, Cardiovascular Research, Henry Ford Hospital Detroit, Education and Research Bldg. Room 4015, 2799 West Grand Boulevard, Detroit, MI 48202-2689 USA
- Present Address: Gerontology Research Center, National Institute on Aging, NIH, 5600 Nathan Shock Drive, Baltimore, MD 21224-6825 USA
| | - John W. Kyle
- Department of Neurobiology, Pharmacology, and Physiology, University of Chicago, Chicago, IL USA
| | - Albertas Undrovinas
- Department of Internal Medicine, Cardiovascular Research, Henry Ford Hospital Detroit, Education and Research Bldg. Room 4015, 2799 West Grand Boulevard, Detroit, MI 48202-2689 USA
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Niebruegge S, Bauwens CL, Peerani R, Thavandiran N, Masse S, Sevaptisidis E, Nanthakumar K, Woodhouse K, Husain M, Kumacheva E, Zandstra PW. Generation of human embryonic stem cell-derived mesoderm and cardiac cells using size-specified aggregates in an oxygen-controlled bioreactor. Biotechnol Bioeng 2009; 102:493-507. [PMID: 18767184 DOI: 10.1002/bit.22065] [Citation(s) in RCA: 176] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The ability to generate human pluripotent stem cell-derived cell types at sufficiently high numbers and in a reproducible manner is fundamental for clinical and biopharmaceutical applications. Current experimental methods for the differentiation of pluripotent cells such as human embryonic stem cells (hESC) rely on the generation of heterogeneous aggregates of cells, also called "embryoid bodies" (EBs), in small scale static culture. These protocols are typically (1) not scalable, (2) result in a wide range of EB sizes and (3) expose cells to fluctuations in physicochemical parameters. With the goal of establishing a robust bioprocess we first screened different scalable suspension systems for their ability to support the growth and differentiation of hESCs. Next homogeneity of initial cell aggregates was improved by employing a micro-printing strategy to generate large numbers of size-specified hESC aggregates. Finally, these technologies were integrated into a fully controlled bioreactor system and the impact of oxygen concentration was investigated. Our results demonstrate the beneficial effects of stirred bioreactor culture, aggregate size-control and hypoxia (4% oxygen tension) on both cell growth and cell differentiation towards cardiomyocytes. QRT-PCR data for markers such as Brachyury, LIM domain homeobox gene Isl-1, Troponin T and Myosin Light Chain 2v, as well as immunohistochemistry and functional analysis by response to chronotropic agents, documented the impact of these parameters on cardiac differentiation. This study provides an important foundation towards the robust generation of clinically relevant numbers of hESC derived cells.
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Affiliation(s)
- Sylvia Niebruegge
- Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, Ontario, Canada
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14
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Pathophysiology and pharmacology of the cardiac “late sodium current”. Pharmacol Ther 2008; 119:326-39. [DOI: 10.1016/j.pharmthera.2008.06.001] [Citation(s) in RCA: 145] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2008] [Accepted: 06/04/2008] [Indexed: 12/19/2022]
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Bocchi L, Vassalle M. Characterization of the slowly inactivating sodium current INa2 in canine cardiac single Purkinje cells. Exp Physiol 2007; 93:347-61. [PMID: 17993508 DOI: 10.1113/expphysiol.2007.040881] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The aim of our experiments was to investigate by means of a whole cell patch-clamp technique the characteristics of the slowly inactivating sodium current (I(Na2)) found in the plateau range in canine cardiac Purkinje single cells. The I(Na2) was separated from the fast-activating and -inactivating I(Na) (labelled here I(Na1)) by applying a two-step protocol. The first step, from a holding potential (V(h)) of -90 or -80 mV to -50 mV, led to the quick activation and inactivation of I(Na1). The second step consisted of depolarizations of increasing amplitude from -50 mV to less negative values, which led to the quick activation and slow inactivation of I(Na2). The I(Na2) was fitted with a double exponential function with time constants of tens and hundreds milliseconds, respectively. After the activation and inactivation of I(Na1) at -50 mV, the slope conductance was very small and did not change with time. Instead, during I(Na2), the slope conductance was larger and decreased as a function of time. Progressively longer conditioning steps at -50 mV resulted in a progressive decrease in amplitude of I(Na2) during the subsequent test steps. Gradually longer hyperpolarizing steps (increments of 100 ms up to 600 ms) from V(h) -30 mV to -100 mV were followed on return to -30 mV by a progressively larger I(Na2), as were gradually more negative 500 ms steps from V(h) -30 mV to -90 mV. At the end of a ramp to -20 mV, a sudden repolarization to approximately -35 mV fully deactivated I(Na2). The I(Na2) was markedly reduced by lignocaine (lidocaine) and by low extracellular [Na(+)], but it was little affected by low and high extracellular [Ca(2+)]. At negative potentials, the results indicate that there was little overlap between I(Na2) and the transient outward current, I(to), as well as the calcium current, I(Ca). In the absence of I(to) and I(Ca) (blocked by means of 4-aminopyridine and nickel, respectively), I(Na2) reversed at 60 mV. In conclusion, I(Na2) is a sodium current that can be initiated after the inactivation of I(Na1) and has characteristics that are quite distinct from those of I(Na1). The results have a bearing on the mechanisms underlying the long plateau of Purkinje cell action potential and its modifications in different physiological and pathological conditions.
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Affiliation(s)
- L Bocchi
- Department of Physiology, State University of New York, Downstate Medical Center, 450 Clarkson Avenue, Brooklyn, NY 11203, USA
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16
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Qu Y, Karnabi E, Chahine M, Vassalle M, Boutjdir M. Expression of skeletal muscle Na(V)1.4 Na channel isoform in canine cardiac Purkinje myocytes. Biochem Biophys Res Commun 2007; 355:28-33. [PMID: 17286959 PMCID: PMC1849952 DOI: 10.1016/j.bbrc.2007.01.101] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2006] [Accepted: 01/16/2007] [Indexed: 12/19/2022]
Abstract
BACKGROUND AND AIM The action potential plateau of Purkinje fibers is particularly sensitive to tetrodotoxin (TTX) and this could be due to a TXX-sensitive Na(+) current. The expression of TTX-sensitive neuronal Na(V)1.1 and Na(V)1.2 isoforms has been reported in canine Purkinje myocytes. Our aim was to investigate by means of biochemical and functional techniques whether the TTX-sensitive skeletal Na(V)1.4 isoform is also expressed in canine cardiac Purkinje myocytes. METHODS AND RESULTS Using Na(V)1.4 specific primers, a PCR product corresponding to Na(V)1.4 was amplified from canine Purkinje fibers RNA and confirmed by sequencing and megablast of the gene bank. Confocal indirect immunostaining using anti-Na(V)1.4 antibody demonstrates distinct sarcolemmal staining pattern compared to that of the cardiac isoform Na(V)1.5. Expression of Na(V)1.4 in tsA201 cells yielded a TTX-sensitive Na(+) current with an IC(50) of 10nM. CONCLUSIONS These results demonstrate the expression of the TTX-sensitive Na(V)1.4 channel in canine cardiac Purkinje myocytes. This novel finding suggests a role of Na(V)1.4 channel in Purkinje myocytes and thus has important clinical implications for the mechanisms and management of ventricular arrhythmias originating in the Purkinje network.
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Affiliation(s)
- Yongxia Qu
- VA New York Harbor Healthcare System, Brooklyn, NY
- SUNY Downstate Medical Center, Brooklyn, NY
| | - Eddy Karnabi
- VA New York Harbor Healthcare System, Brooklyn, NY
- SUNY Downstate Medical Center, Brooklyn, NY
| | - Mohamed Chahine
- Québec Heart Institute, Laval Hospital & Department of Medicine, Laval University, Sainte-Foy, Québec, Canada
| | | | - Mohamed Boutjdir
- VA New York Harbor Healthcare System, Brooklyn, NY
- SUNY Downstate Medical Center, Brooklyn, NY
- NYU School of Medicine, New York, NY
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17
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Fearon IM, Gautier M. Prolonged action potentials in cardiac Purkinje cells: a distinct phenotype arising from a distinct sodium channel. Exp Physiol 2006; 92:1-2. [PMID: 17099058 DOI: 10.1113/expphysiol.2006.036418] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- Ian M Fearon
- Faculty of Life Sciences, The University of Manchester, 2nd Floor, Core Technology Facility, 46 Grafton Street, Manchester M13 9NT, UK.
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