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Jaferzadeh K, Rappaz B, Kim Y, Kim BK, Moon I, Marquet P, Turcatti G. Automated Dual-Mode Cell Monitoring To Simultaneously Explore Calcium Dynamics and Contraction-Relaxation Kinetics within Drug-Treated Stem Cell-Derived Cardiomyocytes. ACS Sens 2023. [PMID: 37335579 DOI: 10.1021/acssensors.3c00073] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/21/2023]
Abstract
This manuscript proposes a new dual-mode cell imaging system for studying the relationships between calcium dynamics and the contractility process of cardiomyocytes derived from human-induced pluripotent stem cells. Practically, this dual-mode cell imaging system provides simultaneously both live cell calcium imaging and quantitative phase imaging based on digital holographic microscopy. Specifically, thanks to the development of a robust automated image analysis, simultaneous measurements of both intracellular calcium, a key player of excitation-contraction coupling, and the quantitative phase image-derived dry mass redistribution, reflecting the effective contractility, namely, the contraction and relaxation processes, were achieved. Practically, the relationships between calcium dynamics and the contraction-relaxation kinetics were investigated in particular through the application of two drugs─namely, isoprenaline and E-4031─known to act precisely on calcium dynamics. Specifically, this new dual-mode cell imaging system enabled us to establish that calcium regulation can be divided into two phases, an early phase influencing the occurrence of the relaxation process followed by a late phase, which although not having a significant influence on the relaxation process affects significantly the beat frequency. In combination with cutting-edge technologies allowing the generation of human stem cell-derived cardiomyocytes, this dual-mode cell monitoring approach therefore represents a very promising technique, particularly in the fields of drug discovery and personalized medicine, to identify compounds likely to act more selectively on specific steps that compose the cardiomyocyte contractility.
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Affiliation(s)
- Keyvan Jaferzadeh
- Department of Robotics & Mechatronics Engineering, DGIST, Daegu 42988, South Korea
| | - Benjamin Rappaz
- Biomolecular Screening Facility, Ecole Polytechnique Fedérale de Lausanne (EPFL), Lausanne 1015, Switzerland
| | - Youhyun Kim
- Department of Robotics & Mechatronics Engineering, DGIST, Daegu 42988, South Korea
| | - Bo-Kyoung Kim
- Biomolecular Screening Facility, Ecole Polytechnique Fedérale de Lausanne (EPFL), Lausanne 1015, Switzerland
| | - Inkyu Moon
- Department of Robotics & Mechatronics Engineering, DGIST, Daegu 42988, South Korea
| | - Pierre Marquet
- International Joint Research Unit in Child Psychiatry, Department of Psychiatry, Lausanne University Hospital, Prilly, Lausanne 1008, Switzerland
- University of Lausanne, Lausanne 1015, Switzerland
- Université Laval, Québec, Québec G1V 0A6, Canada
- Department of Psychiatry and Neuroscience, Université Laval, Quebec, Quebec G1V 0A6, Canada
- CERVO Brain Research Center, CIUSSS de la Capitale-Nationale, Quebec, Québec G1J 2G3, Canada
- Center for Optics, Photonics and Lasers (COPL), Laval University, Quebec, Québec G1V 0A6, Canada
| | - Gerardo Turcatti
- Biomolecular Screening Facility, Ecole Polytechnique Fedérale de Lausanne (EPFL), Lausanne 1015, Switzerland
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Fletcher S, Maddock H, James RS, Wallis R, Gharanei M. The cardiac work-loop technique: An in vitro model for identifying and profiling drug-induced changes in inotropy using rat papillary muscles. Sci Rep 2020; 10:5258. [PMID: 32210283 PMCID: PMC7093439 DOI: 10.1038/s41598-020-58935-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2019] [Accepted: 11/26/2019] [Indexed: 11/09/2022] Open
Abstract
The cardiac work-loop technique closely mimics the intrinsic in vivo movement and characteristics of cardiac muscle function. In this study, six known inotropes were profiled using the work-loop technique to evaluate the potential of this method to predict inotropy. Papillary muscles from male Sprague-Dawley rats were mounted onto an organ bath perfused with Krebs-Henseleit buffer. Following optimisation, work-loop contractions were performed that included an initial stabilisation period followed by vehicle control or drug administration. Six known inotropes were tested: digoxin, dobutamine, isoprenaline, flecainide, verapamil and atenolol. Muscle performance was evaluated by calculating power output during work-loop contraction. Digoxin, dobutamine and isoprenaline caused a significant increase in power output of muscles when compared to vehicle control. Flecainide, verapamil and atenolol significantly reduced power output of muscles. These changes in power output were reflected in alterations in work loop shapes. This is the first study in which changes in work-loop shape detailing for example the activation, shortening or passive re-lengthening have been linked to the mechanism of action of a compound. This study has demonstrated that the work-loop technique can provide an important novel method with which to assess detailed mechanisms of drug-induced effects on cardiac muscle contractility.
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Affiliation(s)
- Sophie Fletcher
- Centre for Sport, Exercise and Life Sciences, Coventry University, Coventry, United Kingdom.,InoCardia Ltd, Technocentre, Puma Way, Coventry, CV1 2TT, UK
| | - Helen Maddock
- Centre for Sport, Exercise and Life Sciences, Coventry University, Coventry, United Kingdom. .,InoCardia Ltd, Technocentre, Puma Way, Coventry, CV1 2TT, UK.
| | - Rob S James
- Centre for Sport, Exercise and Life Sciences, Coventry University, Coventry, United Kingdom
| | - Rob Wallis
- InoCardia Ltd, Technocentre, Puma Way, Coventry, CV1 2TT, UK
| | - Mayel Gharanei
- Centre for Sport, Exercise and Life Sciences, Coventry University, Coventry, United Kingdom.,InoCardia Ltd, Technocentre, Puma Way, Coventry, CV1 2TT, UK
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3
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Pham T, Han JC, Taberner A, Loiselle D. Do right-ventricular trabeculae gain energetic advantage from having a greater velocity of shortening? J Physiol 2017; 595:6477-6488. [PMID: 28857176 DOI: 10.1113/jp274837] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2017] [Accepted: 08/29/2017] [Indexed: 01/22/2023] Open
Abstract
KEY POINTS We designed a study to test whether velocity of shortening in right-ventricular tissue preparations is greater than that of the left side under conditions mimicking those encountered by the heart in vivo. Our experiments allowed us to explore whether greater velocity of shortening results in any energetic advantage. We found that velocity of shortening was higher in the rat right-ventricular trabeculae. These results at the tissue level seem paradoxical to the velocity of ventricular ejection at the organ level, and are not always in accord with shortening of unloaded cells. Despite greater velocity of shortening in right-ventricular trabeculae, they neither gained nor lost advantage with respect to both mechanical efficiency and the heat generated during shortening. ABSTRACT Our study aimed to ascertain whether the interventricular difference of shortening velocity, reported for isolated cardiac tissues in vitro, affects interventricular mechano-energetic performance when tested under physiological conditions using a shortening protocol designed to mimic those in vivo. We isolated trabeculae from both ventricles of the rat, mounted them in a calorimeter, and performed experiments at 37°C and 5 Hz stimulus frequency to emulate conditions of the rat heart in vivo. Each trabecula was subjected to two experimental protocols: (i) isotonic work-loop contractions at a variety of afterloads, and (ii) isometric contractions at a variety of preloads. Velocity of shortening was calculated from the former protocol during the isotonic shortening phase of the contraction. Simultaneous measurements of force-length work and heat output allowed calculation of mechanical efficiency. The shortening-dependent thermal component was quantified from the difference in heat output between the two protocols. Our results show that both extent of shortening and velocity of shortening were higher in trabeculae from the right ventricle. Despite these differences, trabeculae from both ventricles developed the same stress, performed the same work, liberated the same amount of heat, and hence operated at the same mechanical efficiency. Shortening heat was also ventricle independent. The interventricular differences in velocity of shortening and extent of shortening of isolated trabeculae were not manifested in any index of energetics. These collective results underscore the absence of any mechano-energetic advantage or disadvantage conferred on right-ventricular trabeculae arising from their superior velocity of shortening.
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Affiliation(s)
- Toan Pham
- Department of Physiology, University of Auckland, Auckland, New Zealand.,Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
| | - June-Chiew Han
- Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
| | - Andrew Taberner
- Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand.,Department of Engineering Science, University of Auckland, Auckland, New Zealand
| | - Denis Loiselle
- Department of Physiology, University of Auckland, Auckland, New Zealand.,Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
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Helmes M, Najafi A, Palmer BM, Breel E, Rijnveld N, Iannuzzi D, van der Velden J. Mimicking the cardiac cycle in intact cardiomyocytes using diastolic and systolic force clamps; measuring power output. Cardiovasc Res 2016; 111:66-73. [PMID: 27037258 PMCID: PMC5853507 DOI: 10.1093/cvr/cvw072] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/07/2015] [Accepted: 03/26/2016] [Indexed: 01/08/2023] Open
Abstract
Aims A single isolated cardiomyocyte is the smallest functional unit of the heart. Yet, all single isolated cardiomyocyte experiments have been limited by the lack of proper methods that could reproduce a physiological cardiac cycle. We aimed to investigate the contractile properties of a single cardiomyocyte that correctly mimic the cardiac cycle. Methods and results By adjusting the parameters of the feedback loop, using a suitably engineered feedback system and recording the developed force and the length of a single rat cardiomyocyte during contraction and relaxation, we were able to construct force–length (FL) relations analogous to the pressure–volume (PV) relations at the whole heart level. From the cardiac loop graphs, we obtained, for the first time, the power generated by one single cardiomyocyte. Conclusion Here, we introduce a new approach that by combining mechanics, electronics, and a new type optical force transducer can measure the FL relationship of a single isolated cardiomyocyte undergoing a mechanical loop that mimics the PV cycle of a beating heart.
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Affiliation(s)
- Michiel Helmes
- Department of Physiology, VU University Medical Center, Institute for Cardiovascular Research (ICaR-VU), van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands IonOptix Llc., Milton, MA, USA
| | - Aref Najafi
- Department of Physiology, VU University Medical Center, Institute for Cardiovascular Research (ICaR-VU), van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands ICIN-Netherlands Heart Institute, Utrecht, The Netherlands
| | | | - Ernst Breel
- Biophotonics and Medical Imaging and Laserlab, VU University Amsterdam, Amsterdam, The Netherlands Optics11 BV, Amsterdam, The Netherlands
| | | | - Davide Iannuzzi
- Biophotonics and Medical Imaging and Laserlab, VU University Amsterdam, Amsterdam, The Netherlands
| | - Jolanda van der Velden
- Department of Physiology, VU University Medical Center, Institute for Cardiovascular Research (ICaR-VU), van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands ICIN-Netherlands Heart Institute, Utrecht, The Netherlands
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Negroni JA, Morotti S, Lascano EC, Gomes AV, Grandi E, Puglisi JL, Bers DM. β-adrenergic effects on cardiac myofilaments and contraction in an integrated rabbit ventricular myocyte model. J Mol Cell Cardiol 2015; 81:162-75. [PMID: 25724724 DOI: 10.1016/j.yjmcc.2015.02.014] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/15/2014] [Revised: 01/10/2015] [Accepted: 02/17/2015] [Indexed: 12/21/2022]
Abstract
A five-state model of myofilament contraction was integrated into a well-established rabbit ventricular myocyte model of ion channels, Ca(2+) transporters and kinase signaling to analyze the relative contribution of different phosphorylation targets to the overall mechanical response driven by β-adrenergic stimulation (β-AS). β-AS effect on sarcoplasmic reticulum Ca(2+) handling, Ca(2+), K(+) and Cl(-) currents, and Na(+)/K(+)-ATPase properties was included based on experimental data. The inotropic effect on the myofilaments was represented as reduced myofilament Ca(2+) sensitivity (XBCa) and titin stiffness, and increased cross-bridge (XB) cycling rate (XBcy). Assuming independent roles of XBCa and XBcy, the model reproduced experimental β-AS responses on action potentials and Ca(2+) transient amplitude and kinetics. It also replicated the behavior of force-Ca(2+), release-restretch, length-step, stiffness-frequency and force-velocity relationships, and increased force and shortening in isometric and isotonic twitch contractions. The β-AS effect was then switched off from individual targets to analyze their relative impact on contractility. Preventing β-AS effects on L-type Ca(2+) channels or phospholamban limited Ca(2+) transients and contractile responses in parallel, while blocking phospholemman and K(+) channel (IKs) effects enhanced Ca(2+) and inotropy. Removal of β-AS effects from XBCa enhanced contractile force while decreasing peak Ca(2+) (due to greater Ca(2+) buffering), but had less effect on shortening. Conversely, preventing β-AS effects on XBcy preserved Ca(2+) transient effects, but blunted inotropy (both isometric force and especially shortening). Removal of titin effects had little impact on contraction. Finally, exclusion of β-AS from XBCa and XBcy while preserving effects on other targets resulted in preserved peak isometric force response (with slower kinetics) but nearly abolished enhanced shortening. β-AS effects on XBCa and XBcy have greater impact on isometric and isotonic contraction, respectively.
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Affiliation(s)
- Jorge A Negroni
- Department of Comparative, Cellular and Molecular Biology, Universidad Favaloro, Buenos Aires, Argentina.
| | - Stefano Morotti
- Department of Pharmacology, University of California Davis, CA, USA
| | - Elena C Lascano
- Department of Comparative, Cellular and Molecular Biology, Universidad Favaloro, Buenos Aires, Argentina
| | - Aldrin V Gomes
- Department of Neurobiology, Physiology and Behavior, University of California Davis, CA, USA
| | - Eleonora Grandi
- Department of Pharmacology, University of California Davis, CA, USA
| | - José L Puglisi
- Department of Pharmacology, University of California Davis, CA, USA
| | - Donald M Bers
- Department of Pharmacology, University of California Davis, CA, USA.
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Wijnker PJM, Foster DB, Tsao AL, Frazier AH, dos Remedios CG, Murphy AM, Stienen GJM, van der Velden J. Impact of site-specific phosphorylation of protein kinase A sites Ser23 and Ser24 of cardiac troponin I in human cardiomyocytes. Am J Physiol Heart Circ Physiol 2012; 304:H260-8. [PMID: 23144315 DOI: 10.1152/ajpheart.00498.2012] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
PKA-mediated phosphorylation of contractile proteins upon β-adrenergic stimulation plays an important role in the regulation of cardiac performance. Phosphorylation of the PKA sites (Ser(23)/Ser(24)) of cardiac troponin (cTn)I results in a decrease in myofilament Ca(2+) sensitivity and an increase in the rate of relaxation. However, the relation between the level of phosphorylation of the sites and the functional effects in the human myocardium is unknown. Therefore, site-directed mutagenesis was used to study the effects of phosphorylation at Ser(23) and Ser(24) of cTnI on myofilament function in human cardiac tissue. Serines were replaced by aspartic acid (D) or alanine (A) to mimic phosphorylation and dephosphorylation, respectively. cTnI-DD mimics both sites phosphorylated, cTnI-AD mimics Ser(23) unphosphorylated and Ser(24) phosphorylated, cTnI-DA mimics Ser(23) phosphorylated and Ser(24) unphosphorylated, and cTnI-AA mimics both sites unphosphorylated. Force development was measured at various Ca(2+) concentrations in permeabilized cardiomyocytes in which the endogenous troponin complex was exchanged with these recombinant human troponin complexes. In donor cardiomyocytes, myofilament Ca(2+) sensitivity (pCa(50)) was significantly lower in cTnI-DD (pCa(50): 5.39 ± 0.01) compared with cTnI-AA (pCa(50): 5.50 ± 0.01), cTnI-AD (pCa(50): 5.48 ± 0.01), and cTnI-DA (pCa(50): 5.51 ± 0.01) at ~70% cTn exchange. No effects were observed on the rate of tension redevelopment. In cardiomyocytes from idiopathic dilated cardiomyopathic tissue, a linear decline in pCa(50) with cTnI-DD content was observed, saturating at ~55% bisphosphorylation. Our data suggest that in the human myocardium, phosphorylation of both PKA sites on cTnI is required to reduce myofilament Ca(2+) sensitivity, which is maximal at ~55% bisphosphorylated cTnI. The implications for in vivo cardiac function in health and disease are detailed in the DISCUSSION in this article.
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Affiliation(s)
- Paul J M Wijnker
- Laboratory for Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands.
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7
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Taberner AJ, Han JC, Loiselle DS, Nielsen PMF, Nielsen PMF. An innovative work-loop calorimeter for in vitro measurement of the mechanics and energetics of working cardiac trabeculae. J Appl Physiol (1985) 2011; 111:1798-803. [PMID: 21903883 DOI: 10.1152/japplphysiol.00752.2011] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We describe a unique work-loop calorimeter with which we can measure, simultaneously, the rate of heat production and force-length work output of isolated cardiac trabeculae. The mechanics of the force-length work-loop contraction mimic those of the pressure-volume work-loops experienced by the heart. Within the measurement chamber of a flow-through microcalorimeter, a trabecula is electrically stimulated to respond, under software control, in one of three modes: fixed-end, isometric, or isotonic. In each mode, software controls the position of a linear motor, with feedback from muscle force, to adjust muscle length in the desired temporal sequence. In the case of a work-loop contraction, the software achieves seamless transitions between phases of length control (isometric contraction, isometric relaxation, and restoration of resting muscle length) and force control (isotonic shortening). The area enclosed by the resulting force-length loop represents the work done by the trabecula. The change of enthalpy expended by the muscle is given by the sum of the work term and the associated amount of evolved heat. With these simultaneous measurements, we provide the first estimation of suprabasal, net mechanical efficiency (ratio of work to change of enthalpy) of mammalian cardiac trabeculae. The maximum efficiency is at the vicinity of 12%.
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Affiliation(s)
- Andrew J Taberner
- Auckland Bioengineering Institute, The Univ. of Auckland, Auckland, New Zealand.
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8
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BAI Y, TANG A, WANG S, ZHU X. Total internal reflection fluorescence microscopy study of spiral Ca2+waves in single heart cell. J Microsc 2008; 229:555-60. [DOI: 10.1111/j.1365-2818.2008.01943.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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9
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Pillekamp F, Halbach M, Reppel M, Rubenchyk O, Pfannkuche K, Xi JY, Bloch W, Sreeram N, Brockmeier K, Hescheler J. Neonatal Murine Heart Slices. A Robust Model to Study Ventricular Isometric Contractions. Cell Physiol Biochem 2007; 20:837-46. [DOI: 10.1159/000110443] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/20/2007] [Indexed: 11/19/2022] Open
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10
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Lamberts RR, Hamdani N, Soekhoe TW, Boontje NM, Zaremba R, Walker LA, de Tombe PP, van der Velden J, Stienen GJM. Frequency-dependent myofilament Ca2+ desensitization in failing rat myocardium. J Physiol 2007; 582:695-709. [PMID: 17478529 PMCID: PMC2075316 DOI: 10.1113/jphysiol.2007.134486] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The positive force-frequency relation, one of the key factors modulating performance of healthy myocardium, has been attributed to an increased Ca(2+) influx per unit of time. In failing hearts, a blunted, flat or negative force-frequency relation has been found. In healthy and failing hearts frequency-dependent alterations in Ca(2+) sensitivity of the myofilaments, related to different phosphorylation levels of contractile proteins, could contribute to this process. Therefore, the frequency dependency of force, intracellular free Ca(2+) ([Ca(2+)](i)), Ca(2+) sensitivity and contractile protein phosphorylation were determined in control and monocrotaline-treated, failing rat hearts. An increase in frequency from 0.5 to 6 Hz resulted in an increase in force in control (14.3 +/- 3.0 mN mm(-2)) and a decrease in force in failing trabeculae (9.4 +/- 3.2 mN mm(-2)), whereas in both groups the amplitude of [Ca(2+)](i) transient increased. In permeabilized cardiomyocytes, isolated from control hearts paced at 0 and 9 Hz, Ca(2+) sensitivity remained constant with frequency (pCa(50): 5.55 +/- 0.02 and 5.58 +/- 0.01, respectively, P>0.05), whereas in cardiomyocytes from failing hearts Ca(2+) sensitivity decreased with frequency (pCa(50): 5.62 +/- 0.01 and 5.57 +/- 0.01, respectively, P<0.05). After incubation of the cardiomyocytes with protein kinase A (PKA) this frequency dependency of Ca(2+) sensitivity was abolished. Troponin I (TnI) and myosin light chain 2 (MLC2) phosphorylation remained constant in control hearts but both increased with frequency in failing hearts. In conclusion, in heart failure frequency-dependent myofilament Ca(2+) desensitization, through increased TnI phosphorylation, contributes to the negative force-frequency relation and is counteracted by a frequency-dependent MLC2 phosphorylation. We propose a novel role for PKC-mediated TnI phosphorylation in modulating the force-frequency relation.
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Affiliation(s)
- Regis R Lamberts
- Department of Anesthesiology, Institute for Cardiovascular Research (ICaR-VU), VU University Medical Center (VUMC), 1081 BT Amsterdam, The Netherlands.
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11
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Fukuda N, Wu Y, Nair P, Granzier HL. Phosphorylation of titin modulates passive stiffness of cardiac muscle in a titin isoform-dependent manner. ACTA ACUST UNITED AC 2005; 125:257-71. [PMID: 15738048 PMCID: PMC2234012 DOI: 10.1085/jgp.200409177] [Citation(s) in RCA: 151] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We investigated the effect of protein kinase A (PKA) on passive force in skinned cardiac tissues that express different isoforms of titin, i.e., stiff (N2B) and more compliant (N2BA) titins, at different levels. We used rat ventricular (RV), bovine left ventricular (BLV), and bovine left atrial (BLA) muscles (passive force: RV > BLV > BLA, with the ratio of N2B to N2BA titin, ∼90:10, ∼40:60, and ∼10:90%, respectively) and found that N2B and N2BA isoforms can both be phosphorylated by PKA. Under the relaxed condition, sarcomere length was increased and then held constant for 30 min and the peak passive force, stress-relaxation, and steady-state passive force were determined. Following PKA treatment, passive force was significantly decreased in all muscle types with the effect greatest in RV, lowest in BLA, and intermediate in BLV. Fitting the stress-relaxation data to the sum of three exponential decay functions revealed that PKA blunts the magnitude of stress-relaxation and accelerates its time constants. To investigate whether or not PKA-induced decreases in passive force result from possible alteration of titin–thin filament interaction (e.g., via troponin I phosphorylation), we conducted the same experiments using RV preparations that had been treated with gelsolin to extract thin filaments. PKA decreased passive force in gelsolin-treated RV preparations with a magnitude similar to that observed in control preparations. PKA was also found to decrease restoring force in skinned ventricular myocytes of the rat that had been shortened to below the slack length. Finally, we investigated the effect of the β-adrenergic receptor agonist isoprenaline on diastolic force in intact rat ventricular trabeculae. We found that isoprenaline phosphorylated titin and that it reduced diastolic force to a degree similar to that found in skinned RV preparations. Taken together, these results suggest that during β-adrenergic stimulation, PKA increases ventricular compliance in a titin isoform-dependent manner.
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Affiliation(s)
- Norio Fukuda
- Department of Veterinary and Comparative Anatomy, Pharmacology and Physiology, Washington State University, Pullman, WA 99164, USA
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12
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Haworth RS, Cuello F, Herron TJ, Franzen G, Kentish JC, Gautel M, Avkiran M. Protein kinase D is a novel mediator of cardiac troponin I phosphorylation and regulates myofilament function. Circ Res 2004; 95:1091-9. [PMID: 15514163 DOI: 10.1161/01.res.0000149299.34793.3c] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Protein kinase D (PKD) is a serine kinase whose myocardial substrates are unknown. Yeast 2-hybrid screening of a human cardiac library, using the PKD catalytic domain as bait, identified cardiac troponin I (cTnI), myosin-binding protein C (cMyBP-C), and telethonin as PKD-interacting proteins. In vitro phosphorylation assays revealed PKD-mediated phosphorylation of cTnI, cMyBP-C, and telethonin, as well as myomesin. Peptide mass fingerprint analysis of cTnI by liquid chromatography-coupled mass spectrometry indicated PKD-mediated phosphorylation of a peptide containing Ser22 and Ser23, the protein kinase A (PKA) targets. Ser22 and Ser23 were replaced by Ala, either singly (Ser22Ala or Ser23Ala) or jointly (Ser22/23Ala), and the troponin complex reconstituted in vitro, using wild-type or mutated cTnI together with wild-type cardiac troponin C and troponin T. PKD-mediated cTnI phosphorylation was reduced in complexes containing Ser22Ala or Ser23Ala cTnI and completely abolished in the complex containing Ser22/23Ala cTnI, indicating that Ser22 and Ser23 are both targeted by PKD. Furthermore, troponin complex containing wild-type cTnI was phosphorylated with similar kinetics and stoichiometry (approximately 2 mol phosphate/mol cTnI) by both PKD and PKA. To determine the functional impact of PKD-mediated phosphorylation, Ca2+ sensitivity of tension development was studied in a rat skinned ventricular myocyte preparation. PKD-mediated phosphorylation did not affect maximal tension but produced a significant rightward shift of the tension-pCa relationship, indicating reduced myofilament Ca2+ sensitivity. At submaximal Ca2+ activation, PKD-mediated phosphorylation also accelerated isometric crossbridge cycling kinetics. Our data suggest that PKD is a novel mediator of cTnI phosphorylation at the PKA sites and may contribute to the regulation of myofilament function.
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13
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Takimoto E, Soergel DG, Janssen PML, Stull LB, Kass DA, Murphy AM. Frequency- and Afterload-Dependent Cardiac Modulation In Vivo by Troponin I With Constitutively Active Protein Kinase A Phosphorylation Sites. Circ Res 2004; 94:496-504. [PMID: 14726477 DOI: 10.1161/01.res.0000117307.57798.f5] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Acute beta-adrenergic stimulation enhances cardiac contractility, accelerates muscle relaxation, and amplifies the inotropic and lusitropic response to increased stimulation frequency. These effects are modulated by phosphorylation of calcium handling and myofilament proteins such as troponin I (TnI) by protein kinase A (PKA). To more directly delineate the role of TnI PKA phosphorylation, transgenic mice were generated that overexpress cardiac TnI in which the serine residues normally targeted by PKA are mutated to aspartic acid to mimic constitutive phosphorylation (TnIDD22,23). Native cardiac TnI was near completely replaced in one transgenic line as assessed by in vitro phosphorylation, and this led to reduced calcium sensitivity of myofibrillar MgATPase, as expected. TnIDD22,23 mice had mildly enhanced basal systolic and diastolic function, and displayed marked augmentation of frequency-dependent inotropy and relaxation, with a peak frequency response 2-fold greater in mutants than controls (P<0.005). Increasing afterload prolonged relaxation more in nontransgenic than TnIDD22,23 (P<0.02), whereas contractile responses to afterload were similar between these strains. Isoproterenol treatment eliminated the differential force-frequency and afterload response between TnIDD22,23 and controls. In contrast to in vivo studies, isolated isometric trabeculae from nontransgenic and TnIDD22,23 mice had similar basal, isoproterenol-, and frequency-stimulated function, suggesting that muscle shortening may be important to TnI PKA effects. These results support a novel role for cardiac TnI PKA phosphorylation in the rate-dependent enhancement of systolic and diastolic function in vivo and afterload sensitivity of relaxation. These results have implications for cardiac failure in which force-frequency modulation is blunted and afterload relaxation sensitivity increased in association with diminished PKA TnI phosphorylation.
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Affiliation(s)
- Eiki Takimoto
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Md 21205, USA
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Layland J, Grieve DJ, Cave AC, Sparks E, Solaro RJ, Shah AM. Essential role of troponin I in the positive inotropic response to isoprenaline in mouse hearts contracting auxotonically. J Physiol 2004; 556:835-47. [PMID: 14966306 PMCID: PMC1664989 DOI: 10.1113/jphysiol.2004.061176] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
PKA-dependent phosphorylation of cardiac troponin I (cTnI) contributes significantly to beta-adrenergic agonist-induced acceleration of myocardial relaxation (lusitropy). However, the role of PKA-dependent cTnI phosphorylation in the positive inotropic response to beta-adrenergic stimulation is unclear. We studied the contractile response to isoprenaline (10 nm) in isolated hearts and isolated cardiomyocytes from transgenic mice with cardiac-specific expression of slow skeletal TnI (ssTnI, which lacks the N-terminal protein extension containing PKA-sensitive phosphorylation sites in cTnI) and matched wild-type littermate controls. As expected, the lusitropic effect of isoprenaline was significantly blunted in ssTnI hearts. However, the positive inotropic response to isoprenaline was also blunted in ssTnI hearts. This effect was especially prominent for ejection-phase indices in isolated auxotonically loaded ssTnI hearts whereas the positive inotropic response of isovolumic hearts or unloaded isolated myocytes was much less affected. Isoprenaline decreased left ventricular end-systolic volume in wild-type hearts (10.6 +/- 1.6 to 6.2 +/- 0.4 microl at a preload of 20 cmH(2)O; P < 0.05) but not transgenic hearts (11.4 +/- 1.3 to 10.9 +/- 1.3 microl; P= n.s.). Likewise, isoprenaline increased stroke work in control hearts (14.5 +/- 1.0 to 22.5 +/- 1.8 mmHg microl mg(-1); P < 0.05) but not transgenic hearts (15.4 +/- 1.3 to 18.3 +/- 1.2 mmHg microl mg(-1); P= n.s.). The end-systolic pressure-volume relation was increased by isoprenaline to a greater extent in control than transgenic hearts. However, isoprenaline induced a similar rise in intracellular Ca(2+) transients in transgenic and non-transgenic cardiomyocytes. These results indicate that cTnI has a pivotal role in the positive inotropic response of the murine heart to beta-adrenergic stimulation, an effect that is highly dependent on loading conditions and is most evident in the auxotonically loaded ejecting heart.
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Affiliation(s)
- Joanne Layland
- Department of Cardiology, King's College London, SE5 9PJ, UK
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Layland J, Kentish JC. Myofilament-based relaxant effect of isoprenaline revealed during work-loop contractions in rat cardiac trabeculae. J Physiol 2002; 544:171-82. [PMID: 12356890 PMCID: PMC2290578 DOI: 10.1113/jphysiol.2002.022855] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
In cardiac muscle, beta-adrenergic stimulation increases contractile force and accelerates relaxation. The relaxant effect is thought to be due primarily to stimulation of Ca(2+) uptake into the sarcoplasmic reticulum (SR), although changes in myofilament properties may also contribute. The present study investigated the contribution of the myofilaments to the beta-adrenergic response in isolated rat cardiac trabeculae undergoing either isometric or work-loop contractions (involving simultaneous force generation and shortening) at different stimulation frequencies (range 0.25-4.5 Hz). SR-dependent effects were eliminated by treatment with ryanodine (1 microM) and cyclopiazonic acid (30 microM). In isometric contractions during SR inhibition, isoprenaline increased the force but did not alter the time course of the twitch. In contrast, in work-loop contractions, the positive inotropic effect was accompanied by a reduced diastolic force between beats, most apparent at higher frequencies (e.g. diastolic stress fell from 58.6 +/- 5.5 to 28.8 +/- 5.8 mN mm(-2) at 1.5 Hz). This relaxant effect contributed to a beta-adrenoceptor-mediated increase in net work and power output at higher frequencies, by reducing the amount of work required to re-lengthen the muscle. Consequently, the frequency for maximum power output increased from 1.1 +/- 0.1 to 1.6 +/- 0.1 Hz. We conclude that the contribution of myofilament properties to the relaxant effect of beta-stimulation may be of greater significance when force and length are changing simultaneously (as occurs in the heart) than during force development under isometric conditions.
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Affiliation(s)
- Joanne Layland
- Centre for Cardiovascular Biology and Medicine, Kings College London, St Thomas's Campus, Lambeth Palace Road, UK.
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