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Toepfer CN, West TG, Ferenczi MA. Revisiting Frank-Starling: regulatory light chain phosphorylation alters the rate of force redevelopment (ktr ) in a length-dependent fashion. J Physiol 2016; 594:5237-54. [PMID: 27291932 PMCID: PMC5023691 DOI: 10.1113/jp272441] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2016] [Accepted: 06/01/2016] [Indexed: 11/24/2022] Open
Abstract
Key points Regulatory light chain (RLC) phosphorylation has been shown to alter the ability of muscle to produce force and power during shortening and to alter the rate of force redevelopment (ktr) at submaximal [Ca2+]. Increasing RLC phosphorylation ∼50% from the in vivo level in maximally [Ca2+]‐activated cardiac trabecula accelerates ktr. Decreasing RLC phosphorylation to ∼70% of the in vivo control level slows ktr and reduces force generation. ktr is dependent on sarcomere length in the physiological range 1.85–1.94 μm and RLC phosphorylation modulates this response. We demonstrate that Frank–Starling is evident at maximal [Ca2+] activation and therefore does not necessarily require length‐dependent change in [Ca2+]‐sensitivity of thin filament activation. The stretch response is modulated by changes in RLC phosphorylation, pinpointing RLC phosphorylation as a modulator of the Frank–Starling law in the heart. These data provide an explanation for slowed systolic function in the intact heart in response to RLC phosphorylation reduction.
Abstract Force and power in cardiac muscle have a known dependence on phosphorylation of the myosin‐associated regulatory light chain (RLC). We explore the effect of RLC phosphorylation on the ability of cardiac preparations to redevelop force (ktr) in maximally activating [Ca2+]. Activation was achieved by rapidly increasing the temperature (temperature‐jump of 0.5–20ºC) of permeabilized trabeculae over a physiological range of sarcomere lengths (1.85–1.94 μm). The trabeculae were subjected to shortening ramps over a range of velocities and the extent of RLC phosphorylation was varied. The latter was achieved using an RLC‐exchange technique, which avoids changes in the phosphorylation level of other proteins. The results show that increasing RLC phosphorylation by 50% accelerates ktr by ∼50%, irrespective of the sarcomere length, whereas decreasing phosphorylation by 30% slows ktr by ∼50%, relative to the ktr obtained for in vivo phosphorylation. Clearly, phosphorylation affects the magnitude of ktr following step shortening or ramp shortening. Using a two‐state model, we explore the effect of RLC phosphorylation on the kinetics of force development, which proposes that phosphorylation affects the kinetics of both attachment and detachment of cross‐bridges. In summary, RLC phosphorylation affects the rate and extent of force redevelopment. These findings were obtained in maximally activated muscle at saturating [Ca2+] and are not explained by changes in the Ca2+‐sensitivity of acto‐myosin interactions. The length‐dependence of the rate of force redevelopment, together with the modulation by the state of RLC phosphorylation, suggests that these effects play a role in the Frank–Starling law of the heart. Regulatory light chain (RLC) phosphorylation has been shown to alter the ability of muscle to produce force and power during shortening and to alter the rate of force redevelopment (ktr) at submaximal [Ca2+]. Increasing RLC phosphorylation ∼50% from the in vivo level in maximally [Ca2+]‐activated cardiac trabecula accelerates ktr. Decreasing RLC phosphorylation to ∼70% of the in vivo control level slows ktr and reduces force generation. ktr is dependent on sarcomere length in the physiological range 1.85–1.94 μm and RLC phosphorylation modulates this response. We demonstrate that Frank–Starling is evident at maximal [Ca2+] activation and therefore does not necessarily require length‐dependent change in [Ca2+]‐sensitivity of thin filament activation. The stretch response is modulated by changes in RLC phosphorylation, pinpointing RLC phosphorylation as a modulator of the Frank–Starling law in the heart. These data provide an explanation for slowed systolic function in the intact heart in response to RLC phosphorylation reduction.
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Affiliation(s)
- Christopher N Toepfer
- Molecular Medicine Section, National Heart and Lung Institute, Imperial College London, London, UK. .,Laboratory of Molecular Physiology, NHLBI, National Institutes of Health, Bethesda, MD, USA.
| | - Timothy G West
- Structure & Motion Laboratory, Royal Veterinary College London, North Mymms, UK
| | - Michael A Ferenczi
- Molecular Medicine Section, National Heart and Lung Institute, Imperial College London, London, UK.,Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, Singapore
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Breuer T, Maes K, Rossaint R, Marx G, Scheers H, Bergs I, Bleilevens C, Gayan-Ramirez G, Bruells CS. Sevoflurane Exposure Prevents Diaphragmatic Oxidative Stress During Mechanical Ventilation but Reduces Force and Affects Protein Metabolism Even During Spontaneous Breathing in a Rat Model. Anesth Analg 2015; 121:73-80. [DOI: 10.1213/ane.0000000000000736] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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She YJ, Wang HZ, Huang JX, Tan YH, Wang ZX, Tian H, Song XR. Effect of a bolus dose of fentanyl on the ED₅₀ and ED₉₅ of sevoflurane in neonates. Med Sci Monit 2014; 20:2658-65. [PMID: 25503557 PMCID: PMC4271805 DOI: 10.12659/msm.891276] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Background The minimum alveolar concentration (MAC) of sevoflurane in neonates is 3.3%, but this value has not been verified in Chinese neonates and the effect of different doses of fentanyl on MAC in neonates has not been investigated. This study was designed to determine the ED50 and ED95 values of sevoflurane in Chinese neonates with and without fentanyl. Material/Methods Ninety-three neonates were randomly assigned to receive sevoflurane alone (control group, n=30), 1 μg/kg sevoflurane (group fent1, n=29), or 2 μg/kg fentanyl (group fent2, n=32). Following inhalational induction and tracheal intubation, the end-tidal concentration of sevoflurane was adjusted to achieve the designated concentration, which was determined using the modified Dixon’s up-and-down method starting with 3.0% in each group, with a 0.25% step size. Success was defined as no motor response within 60 s of skin incision. Results The MAC (standard deviation) values of sevoflurane were 2.91% (0.27) in the control group, 2.53% (0.31) in the fent1 group, and 2.34% (0.33) in the fent2 group according to Dixon’s up-and-down method. Logistic probit regression analysis revealed that the ED50 and ED95 (95% CI) of sevoflurane in neonates were 2.82% (2.66–2.98) and 3.39% (2.89–3.89), respectively, in the control group; 2.44% (2.19–2.68) and 3.30% (2.51–4.09), respectively, in the fent1 group; and 2.21% (1.97–2.45) and 3.11% (2.35–3.88), respectively, in the fent2 group. Conclusions The MAC value of sevoflurane in Chinese neonates was lower than previously reported and was reduced by the addition of fentanyl.
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Affiliation(s)
- Ying-Jun She
- Department of Anesthesiology, Guangzhou Women and Children Medical Center, Guangzhou Medical University affiliated Women and Children Medical Center, Guangzhou, China (mainland)
| | - Huai-Zhen Wang
- Department of Anesthesiology, Guangzhou Women and Children Medical Center, Guangzhou Medical University affiliated Women and Children Medical Center, Guangzhou, China (mainland)
| | - Jun-Xiang Huang
- Department of Anesthesiology, Guangzhou Women and Children Medical Center, Guangzhou Medical University affiliated Women and Children Medical Center, Guangzhou, China (mainland)
| | - Yong-Hong Tan
- Department of Anesthesiology, Guangzhou Women and Children Medical Center, Guangzhou Medical University affiliated Women and Children Medical Center, Guangzhou, China (mainland)
| | - Zi-Xing Wang
- Department of Anesthesiology, Guangzhou Women and Children Medical Center, Guangzhou Medical University affiliated Women and Children Medical Center, Guangzhou, China (mainland)
| | - Hang Tian
- Department of Anesthesiology, Guangzhou Women and Children Medical Center, Guangzhou Medical University affiliated Women and Children Medical Center, Guangzhou, China (mainland)
| | - Xing-Rong Song
- Department of Anesthesiology, Guangzhou Women and Children Medical Center, Guangzhou Medical University affiliated Women and Children Medical Center, Guangzhou, China (mainland)
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Bains R, Moe MC, Vinje ML, Berg-Johnsen J. Isoflurane-induced depolarization of neural mitochondria increases with age. Acta Anaesthesiol Scand 2009; 53:85-92. [PMID: 19032572 DOI: 10.1111/j.1399-6576.2008.01823.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
BACKGROUND AND OBJECTIVES The mitochondrial membrane potential (DeltaPsi(m)) drives the three fundamental functions of mitochondria, namely adenosine triphosphate (ATP) generation, Ca(2+) uptake/storage, and generation/detoxification of ROS. Isoflurane depolarizes neural mitochondria. The sensitivity for general anesthetics increases with age, but the mechanism for this age-related sensitivity is still unknown. We compared the effect of isoflurane on [Ca(2+)](i) and DeltaPsi(m) in isolated pre-synaptic terminals (synaptosomes) from neonatal, adolescent, and adult rats and the influence of interventions in the respiratory chain was assessed. METHODS Synaptosomes were loaded with the fluorescent probes fura-2 ([Ca(2+)](i)) and JC-1 (DeltaPsi(m)) and exposed to isoflurane 1 and 2 minimum alveolar concentration (MAC). The effect on the electron transport chain was investigated by blocking complexes I and V. RESULTS In neonatal rats isoflurane had no significant effect on DeltaPsi(m). In adolescent and adult synaptosomes, however, isoflurane 1 and 2 MAC decreased DeltaPsi(m). Isoflurane 2 MAC increased [Ca(2+)](i) in neonatal and adolescent rats, but not in adult synaptosomes. In Ca(2+)-depleted medium, isoflurane still decreased DeltaPsi(m), while [Ca(2+)](i) remained unaltered. By blocking complex V of the respiratory chain, the isoflurane-induced mitochondrial depolarization was enhanced in all age groups. Blocking complex I depolarized the mitochondria to the same extent as isoflurane 2 MAC, but without any additive effect. CONCLUSIONS The depolarizing effect of isoflurane on neural mitochondria is more pronounced in the adolescent and adult than in neonatal synaptosomes. The increased mitochondrial sensitivity with age seems to be related to the reversed function of the ATP synthase of the electron transport chain.
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Affiliation(s)
- Ravi Bains
- Institute for Surgical Research and Department of Neurosurgery, Rikshospitalet HF, Oslo, Norway.
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Breukelmann D, Housmans PR. Halothane, isoflurane, and sevoflurane increase the kinetics of Ca2+-induced conformational change of recombinant human cardiac troponin C. Anesth Analg 2007; 104:332-7. [PMID: 17242089 DOI: 10.1213/01.ane.0000252432.51717.9f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
BACKGROUND Halothane, isoflurane, and sevoflurane exert negative inotropic side effects, generally mediated via a reduced availability of intracellular calcium. Other possible mechanisms include modified intracellular calcium handling, impaired actomyosin cross-bridge cycling, and/or alteration of calcium-induced conformational changes of the regulatory troponin complex. METHODS We investigated the effect of halothane, isoflurane, and sevoflurane on calcium-dependent kinetics of isolated human recombinant cardiac troponin C labeled with IAANS (HrcTnC(IAANS)) using stopped-flow and calcium titration techniques. RESULTS Calcium concentration at half-maximal fluorescence intensity (K(d)) in the control group was 2.1 +/- 0.1 mM. Volatile anesthetics increased calcium sensitivity in a concentration-dependent fashion sevoflurane (K(d) 1.5-1.7 mM, P = 0.001) > halothane (K(d) 1.7-1.9 mM, P < 0.01) > isoflurane (K(d) 1.8-1.9 mM, P < 0.05). The rate constant of conformational changes after rapid dissociation of calcium from HrcTnC(IAANS) (k(off(c))) was moderately prolonged at 4 degrees C by halothane and isoflurane > sevoflurane. CONCLUSION These mechanisms may counteract the effects of lower calcium availability, and can be responsible for abbreviated, and possibly incomplete, relaxation of cardiac muscle fibers in the presence of volatile anesthetics.
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Affiliation(s)
- Dirk Breukelmann
- Department of Anesthesiology and Intensive Care, University of Muenster, Muenster, Germany.
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Graham MD, Bru-Mercier G, Hopkins PM, Harrison SM. Transient and sustained changes in myofilament sensitivity to Ca2+ contribute to the inotropic effects of sevoflurane in rat ventricle. Br J Anaesth 2004; 94:279-86. [PMID: 15608045 DOI: 10.1093/bja/aei053] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
BACKGROUND The volatile anaesthetics isoflurane and sevoflurane induce both negative and positive inotropic effects in ventricular myocytes, the mechanisms of which are not fully understood. Previous data suggest that changes in myofilament Ca(2+) sensitivity contribute to their sustained negative inotropic effects. In this study, the role of changes in myofilament Ca(2+) sensitivity in both positive and negative inotropic effects of these agents was examined in intact ventricular myocytes. METHODS Contractility and cytosolic Ca(2+) (fura-2) were recorded optically in ventricular myocytes stimulated electrically (1 Hz) at 30 degrees C. Myofilament Ca(2+) sensitivity was assessed from plots of cell length against fura-2 fluorescence ratio (Fr) from individual twitches at various points before, during and after a 1 or 4 min exposure to 0.6 mM anaesthetic. RESULTS Isoflurane reduced mean (sd) myofilament Ca(2+) sensitivity from 10.3 (1.9) to 5.9 (1.6) microm Fr(-1) (P<0.001) throughout a 1 min exposure, which returned to control on removal. In contrast, on initial exposure to sevoflurane, Ca(2+) sensitivity was reduced from 10.8 (1.3) to 4.3 (0.9) microm Fr(-1) (P<0.001) but this recovered partially towards control over 3 min. On removal, sensitivity was increased above control (to 17.7 (2.2) microm Fr(-1); P<0.001) before preanaesthetic levels were restored. CONCLUSIONS These data show that both isoflurane and sevoflurane reduce apparent myofilament Ca(2+) sensitivity at steady state. However, sevoflurane (but not isoflurane) induced transient changes in apparent myofilament Ca(2+) sensitivity, which would contribute to its inotropic profile.
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Affiliation(s)
- M D Graham
- School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, UK
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Langeron O, Bouhemad B, Orliaguet G, Coriat P, Lecarpentier Y, Riou B. Effects of halogenated anaesthetics on diaphragmatic actin-myosin cross-bridge kinetics. Br J Anaesth 2003; 90:759-65. [PMID: 12765892 DOI: 10.1093/bja/aeg140] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
BACKGROUND The effects of halogenated anaesthetics on cross-bridge (CB) kinetics are unclear. As halogenated anaesthetics do not markedly modify the intracellular calcium transient in the diaphragm, we used an isolated rat diaphragm preparation to assess the effects of halothane and isoflurane on CB kinetics. METHODS The effects of halothane and isoflurane (1 and 2 minimum alveolar concentration (MAC)) on rat diaphragm muscle strips were studied in vitro (Krebs-Henseleit solution, 29 degrees C, oxygen 95%/carbon dioxide 5%) in tetanus mode (50 Hz). From the force-velocity curve and using A. F. Huxley's equations, we determined the main mechanical and energetic variables and calculated CB kinetics. RESULTS At 1 and 2 MAC, isoflurane and halothane induced no significant inotropic effects. Whatever the concentrations tested, halothane and isoflurane did not significantly modify the CB number, the elementary force per CB, the attachment and detachment constants, the duration of the CB cycle and mean CB velocity. CONCLUSION In the rat diaphragm at therapeutic concentrations, halogenated anaesthetics do not significantly modify CB mechanical and kinetic properties.
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Affiliation(s)
- O Langeron
- Department of Anaesthesiology and Critical Care, Centre Hospitalier Universitaire (CHU) Pitié-Salpêtrière, Assistance Publique-Hôpitaux de Paris (AP-HP), Université Pierre et Marie Curie, Paris, France.
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Bartunek AE, Claes VA, Housmans PR. Effects of volatile anesthetics on elastic stiffness in isometrically contracting ferret ventricular myocardium. J Appl Physiol (1985) 2002; 92:2491-500. [PMID: 12015364 DOI: 10.1152/japplphysiol.00841.2001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The effects of halothane, isoflurane, and sevoflurane on elastic stiffness, which reflects the degree of cross-bridge attachment, were studied in intact cardiac muscle. Electrically stimulated (0.25 Hz, 25 degrees C), isometrically twitching right ventricular ferret papillary muscles (n = 15) at optimal length (L(max)) were subjected to sinusoidal length oscillations (40 Hz, 0.25- 0.50% of L(max) peak to peak). The amplitude and phase relationship with the resulting force oscillations was decomposed into elastic and viscous components of total stiffness in real time. Increasing extracellular Ca(2+) concentration in the presence of anesthetics to produce peak force equal to control increased elastic stiffness during relaxation, which suggests a direct effect of halothane and sevoflurane on cross bridges.
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Affiliation(s)
- Anna E Bartunek
- Department of Anesthesiology, Mayo Foundation, Rochester, Minnesota 55905, USA
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Bartunek AE, Claes VA, Housmans PR. Effects of volatile anesthetics on stiffness of mammalian ventricular muscle. J Appl Physiol (1985) 2001; 91:1563-73. [PMID: 11568137 DOI: 10.1152/jappl.2001.91.4.1563] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
To assess the effects of halothane, isoflurane, and sevoflurane on cross bridges in intact cardiac muscle, electrically stimulated (0.25 Hz, 25 degrees C) right ventricular ferret papillary muscles (n = 14) were subjected to sinusoidal load oscillations (37-182 Hz, 0.2-0.5 mN peak to peak) at the instantaneous self-resonant frequency of the muscle-lever system. At resonance, stiffness is proportional to m * omega(2) (where m is equivalent moving mass and omega is angular frequency). Dynamic stiffness was derived by relating total stiffness to values of passive stiffness at each length during shortening and lengthening. Shortening amplitude and dynamic stiffness were decreased by halothane > isoflurane > or = sevoflurane. At equal peak shortening, dynamic stiffness was higher in halothane or isoflurane in high extracellular Ca(2+) concentration than in control. Halothane and isoflurane increased passive stiffness. The decrease in dynamic stiffness and shortening results in part from direct effects of volatile anesthetics at the level of cross bridges. The increase in passive stiffness caused by halothane and isoflurane may reflect an effect on weakly bound cross bridges and/or an effect on passive elastic elements.
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Affiliation(s)
- A E Bartunek
- Department of Anesthesiology, Mayo Foundation, 200 First St. SW, Rochester, MN 55905, USA
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Abstract
The volatile anesthetics halothane, isoflurane, and sevoflurane depress myocardial contractility by decreasing transsarcolemmal Ca2+ influx, Ca2+ release from the sarcoplasmic reticulum, Ca2+ sensitivity of the contractile proteins, and cross-bridge performance. The aim of this study is to assess and compare the effects of halothane, isoflurane, and sevoflurane on contractility in conditions in which sarcoplasmic reticulum Ca2+ release is abolished by pretreatment with ryanodine. Ferret right ventricular papillary muscles were exposed to ryanodine at 10(-6) M and then to incremental concentrations of halothane, isoflurane, or sevoflurane. In the presence of ryanodine, each anesthetic decreased isometric and isotonic contractility in a reversible, concentration-dependent manner with no differences between anesthetics and with little or no effect on time variables. It is likely that differences between anesthetic effects on contraction amplitude in isometric and isotonic twitches reside in their effects on the sarcoplasmic reticulum.
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Affiliation(s)
- P R Housmans
- Department of Anesthesiology, Mayo Foundation, Rochester, Minnesota 55905, USA.
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Abstract
We examined the influence of two clinically relevant concentrations (1 and 2 MAC (minimum alveolar concentration)) of halothane and sevoflurane on both efflux and reverse modes of Na+-Ca2+ exchange (NCX) in enzymatically dissociated adult rat cardiac myocytes. We hypothesised that a volatile anaesthetic-induced decrease in myocardial contractility is mediated by a reduction in intracellular calcium concentration ([Ca2+]i) via inhibition of NCX. Cells were exposed to cyclopiazonic acid and zero extracellular Na+ and Ca2+ to block sacroplasmic reticulum (SR) re-uptake and NCX efflux, respectively. As [Ca2+]i increased under these conditions, extracellular Na+ was rapidly (< 300 ms) reintroduced in the presence or absence of a volatile anaesthetic to selectively promote Ca2+ efflux via NCX. Other cells exposed to cyclopiazonic acid and ryanodine to inhibit SR Ca2+ re-uptake and release were Na+ loaded in zero extracellular Ca2+. The reintroduction of extracellular Ca2+ was used to selectively activate Ca2+ influx via NCX. Compared to controls, both 1 and 2 MAC halothane as well as sevoflurane reduced NCX-mediated efflux. The reduction in NCX-mediated influx was concentration dependent, but comparable between the two anaesthetics. Both anaesthetics at each concentration also shifted the relationship between extracellular Na+ (or extent of Na+ loading) and NCX-mediated efflux (or influx) to the right. These data indicate that despite inhibition of NCX-mediated Ca2+ efflux, volatile anaesthetics produce myocardial depression. However, the inhibition of NCX-mediated Ca2+ influx may contribute to decreased cardiac contractility. The overall effect of volatile anaesthetics on the [Ca2+]i profile is likely to be determined by the relative contributions of influx vs. efflux via NCX during each cardiac cycle.
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Affiliation(s)
- I Seckin
- Department of Anaesthesiology, Mayo Clinic and Foundation, Rochester, MN 55905, USA
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Miller T, Szczesna D, Housmans PR, Zhao J, de Freitas F, Gomes AV, Culbreath L, McCue J, Wang Y, Xu Y, Kerrick WG, Potter JD. Abnormal contractile function in transgenic mice expressing a familial hypertrophic cardiomyopathy-linked troponin T (I79N) mutation. J Biol Chem 2001; 276:3743-55. [PMID: 11060294 DOI: 10.1074/jbc.m006746200] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
This study characterizes a transgenic animal model for the troponin T (TnT) mutation (I79N) associated with familial hypertrophic cardiomyopathy. To study the functional consequences of this mutation, we examined a wild type and two I79N-transgenic mouse lines of human cardiac TnT driven by a murine alpha-myosin heavy chain promoter. Extensive characterization of the transgenic I79N lines compared with wild type and/or nontransgenic mice demonstrated: 1) normal survival and no cardiac hypertrophy even with chronic exercise; 2) large increases in Ca(2+) sensitivity of ATPase activity and force in skinned fibers; 3) a substantial increase in the rate of force activation and an increase in the rate of force relaxation; 4) lower maximal force/cross-sectional area and ATPase activity; 5) loss of sensitivity to pH-induced shifts in the Ca(2+) dependence of force; and 6) computer simulations that reproduced experimental observations and suggested that the I79N mutation decreases the apparent off rate of Ca(2+) from troponin C and increases cross-bridge detachment rate g. Simulations for intact living fibers predict a higher basal contractility, a faster rate of force development, slower relaxation, and increased resting tension in transgenic I79N myocardium compared with transgenic wild type. These mechanisms may contribute to mortality in humans, especially in stimulated contractile states.
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Affiliation(s)
- T Miller
- University of Miami School of Medicine, Departments of Molecular and Cellular Pharmacology and Physiology and Biophysics, Miami, Florida 33136 and the Department of Anesthesiology, Mayo Foundation, Rochester, Minnesota 55905
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Bartunek AE, Housmans PR. Effects of sevoflurane on the contractility of ferret ventricular myocardium. J Appl Physiol (1985) 2000; 89:1778-86. [PMID: 11053326 DOI: 10.1152/jappl.2000.89.5.1778] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Isotonic and isometric variables of contractility and relaxation of isolated ferret right ventricular papillary muscles were measured before and during exposure to incremental concentrations of sevoflurane (0-4.9% vol/vol) (30 degrees C) (n = 9). In a second group of muscles (n = 8), effects of sevoflurane were compared with those of low [Ca(2+)](o) (0.45-2.25 mM in steps of 0.45 mM). Sevoflurane caused a reversible concentration-dependent decrease in contractility (ED(50) of developed force 4.6+/-0.9% vol/vol). When compared with twitches of equal amplitude in low extracellular Ca(2+) concentration, sevoflurane accelerated both isometric and isotonic relaxation. The myocardial depressant effect of sevoflurane is less than that of isoflurane and results mainly from a decrease of intracellular Ca(2+) availability. The abbreviated isometric relaxation likely reflects a decrease in Ca(2+) sensitivity and the faster isotonic relaxation may reflect a mild stimulation of Ca(2+) uptake by the sarcoplasmic reticulum.
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Affiliation(s)
- A E Bartunek
- Department of Anesthesiology, Mayo Foundation, Rochester, Minnesota 55905, USA
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