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Okishige K, Tachibana S, Shigeta T, Yamauchi Y, Tanno K, Hirao K, Sasano T. Novel method to avoid serious injurious effects on the atrioventricular nodal (AVN) conduction during catheter ablation of the AVN slow pathway utilizing cryofreezing energy. J Cardiol 2024; 83:371-376. [PMID: 37714263 DOI: 10.1016/j.jjcc.2023.09.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/17/2023] [Revised: 09/04/2023] [Accepted: 09/08/2023] [Indexed: 09/17/2023]
Abstract
BACKGROUND Slow pathway elimination of the atrioventricular node (AVN) is essential to treat AVN reentrant tachycardia (AVNRT). However, injury to the AVN conduction (IAVN) is one of the serious complications. Cryofreezing energy is expected to reduce the incidence of IAVN. This study aimed to investigate the usefulness of a novel method to avoid IAVN during cryoablation of AVNRT. METHODS A total of 157 patients (average age, 65.8 years; male, 71) suffering from AVNRT were included. Once the AVNRT terminated during cryo-ablation, then rapid atrial constant pacing (RACP) was performed during freezing at a rate lower 10 bpm than that inducing Wenchebach AV block in 74 (47.1 %) patients (Group A). The RACP rate was decreasingly reduced by 10 bpm in case of the occurrence of IAVN. When the RACP reached 100 bpm, the cryoablation was prematurely terminated. Group B patients (83 = 52.9 %) underwent cryoablation during sinus rhythm. All patients were allocated in a randomized fashion. We compared the severity of the IAVN between Groups A and B. RESULTS There were no significant differences at 12 months regarding the freedom from the AVNRT between Groups A and B. However, the duration of the IAVN was significantly longer in Group B than A (p = 0.02). There were no significant differences regarding the distance between the His recording sites and successful ablation sites between Groups A and B. No permanent IAVN requiring pacemaker implantation was provoked in either group. CONCLUSION RACP was useful to avoid sustained and serious IAVN during cryoablation of AVNRT.
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Affiliation(s)
- Kaoru Okishige
- Heart Center, Japan Red Cross Yokohama City Bay Hospital, Yokohama, Japan.
| | - Shinichi Tachibana
- Heart Center, Japan Red Cross Yokohama City Bay Hospital, Yokohama, Japan
| | - Takatoshi Shigeta
- Heart Center, Japan Red Cross Yokohama City Bay Hospital, Yokohama, Japan
| | - Yasuteru Yamauchi
- Heart Center, Japan Red Cross Yokohama City Bay Hospital, Yokohama, Japan
| | - Kaoru Tanno
- Cardiology, Showa University, School of Medicine, Tokyo, Japan
| | - Kenzo Hirao
- Arrhythmia Center, Tokyo Medical and Dental University, Tokyo, Japan
| | - Tetsuo Sasano
- Arrhythmia Center, Tokyo Medical and Dental University, Tokyo, Japan
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Kanade PP, Oyunbaatar NE, Lee DW. Effects of low temperature on electrophysiology and mechanophysiology of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). MICRO AND NANO SYSTEMS LETTERS 2021. [DOI: 10.1186/s40486-021-00135-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
AbstractStudies related to low temperature and their effect on cardiomyocytes are essential as hypothermia—like situations have been known to induce arrhythmia or ventricular fibrillation. Till date, several studies have been carried out on animals and their electrophysiological responses have been studied in the form of action potential. However, for a complete assessment of the effect of low temperature, mechanophysiological changes along with electrophysiological changes need to be investigated, at the tissue level. In this study, the effect of culture temperature on cell growth has been studied by measuring the field potential and contractility of human induced pluripotent stem cell-derived cardiomyocytes. This study has the potential to further improve the understanding of low temperature on human cells.
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Tveita T, Sieck GC. Physiological Impact of Hypothermia: The Good, the Bad and the Ugly. Physiology (Bethesda) 2021; 37:69-87. [PMID: 34632808 DOI: 10.1152/physiol.00025.2021] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Hypothermia is defined as a core body temperature of < 35°C, and as body temperature is reduced the impact on physiological processes can be beneficial or detrimental. The beneficial effect of hypothermia enables circulation of cooled experimental animals to be interrupted for 1-2 h without creating harmful effects, while tolerance of circulation arrest in normothermia is between 4 and 5 min. This striking difference has attracted so many investigators, experimental as well as clinical, to this field, and this discovery was fundamental for introducing therapeutic hypothermia in modern clinical medicine in the 1950's. Together with the introduction of cardiopulmonary bypass, therapeutic hypothermia has been the cornerstone in the development of modern cardiac surgery. Therapeutic hypothermia also has an undisputed role as a protective agent in organ transplantation and as a therapeutic adjuvant for cerebral protection in neonatal encephalopathy. However, the introduction of therapeutic hypothermia for organ protection during neurosurgical procedures or as a scavenger after brain and spinal trauma has been less successful. In general, the best neuroprotection seems to be obtained by avoiding hyperthermia in injured patients. Accidental hypothermia occurs when endogenous temperature control mechanisms are incapable of maintaining core body temperature within physiologic limits and core temperature becomes dependent on ambient temperature. During hypothermia spontaneous circulation is considerably reduced and with deep and/or prolonged cooling, circulatory failure may occur, which may limit safe survival of the cooled patient. Challenges that limit safe rewarming of accidental hypothermia patients include cardiac arrhythmias, uncontrolled bleeding, and "rewarming shock".
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Affiliation(s)
- Torkjel Tveita
- Anesthesia and Critical Care Research Group, Department of Clinical Medicine, UiT The Arctic University of Norway, Tromsø, Norway.,Division of Surgical Medicine and Intensive Care, University Hospital of North Norway, Tromsø, Norway
| | - Gary C Sieck
- Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, United States
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Averin AS, Zakharova NM, Tarlachkov SV. Effect of Cooling on Force-Frequency Relationship, Rest Potentiation, and Frequency-Dependent Acceleration of Relaxation in the Guinea Pig Myocardium. J EVOL BIOCHEM PHYS+ 2021. [DOI: 10.1134/s0022093021040025] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Olgar Y, Tuncay E, Degirmenci S, Billur D, Dhingra R, Kirshenbaum L, Turan B. Ageing-associated increase in SGLT2 disrupts mitochondrial/sarcoplasmic reticulum Ca 2+ homeostasis and promotes cardiac dysfunction. J Cell Mol Med 2020; 24:8567-8578. [PMID: 32652890 PMCID: PMC7412693 DOI: 10.1111/jcmm.15483] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Revised: 04/30/2020] [Accepted: 05/24/2020] [Indexed: 12/12/2022] Open
Abstract
The prevalence of death from cardiovascular disease is significantly higher in elderly populations; the underlying factors that contribute to the age‐associated decline in cardiac performance are poorly understood. Herein, we identify the involvement of sodium/glucose co‐transporter gene (SGLT2) in disrupted cellular Ca2+‐homeostasis, and mitochondrial dysfunction in age‐associated cardiac dysfunction. In contrast to younger rats (6‐month of age), older rats (24‐month of age) exhibited severe cardiac ultrastructural defects, including deformed, fragmented mitochondria with high electron densities. Cardiomyocytes isolated from aged rats demonstrated increased reactive oxygen species (ROS), loss of mitochondrial membrane potential and altered mitochondrial dynamics, compared with younger controls. Moreover, mitochondrial defects were accompanied by mitochondrial and cytosolic Ca2+ ([Ca2+]i) overload, indicative of disrupted cellular Ca2+‐homeostasis. Interestingly, increased [Ca2+]i coincided with decreased phosphorylation of phospholamban (PLB) and contractility. Aged‐cardiomyocytes also displayed high Na+/Ca2+‐exchanger (NCX) activity and blood glucose levels compared with young‐controls. Interestingly, the protein level of SGLT2 was dramatically increased in the aged cardiomyocytes. Moreover, SGLT2 inhibition was sufficient to restore age‐associated defects in [Ca2+]i‐homeostasis, PLB phosphorylation, NCX activity and mitochondrial Ca2+‐loading. Hence, the present data suggest that deregulated SGLT2 during ageing disrupts mitochondrial function and cardiac contractility through a mechanism that impinges upon [Ca2+]i‐homeostasis. Our studies support the notion that interventions that modulate SGLT2‐activity can provide benefits in maintaining [Ca2+]i and cardiac function with advanced age.
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Affiliation(s)
- Yusuf Olgar
- Departments of Biophysics, Ankara University Faculty of Medicine, Ankara, Turkey
| | - Erkan Tuncay
- Departments of Biophysics, Ankara University Faculty of Medicine, Ankara, Turkey
| | - Sinan Degirmenci
- Departments of Biophysics, Ankara University Faculty of Medicine, Ankara, Turkey
| | - Deniz Billur
- Departments of Histology-Embriyology, Ankara University Faculty of Medicine, Ankara, Turkey
| | - Rimpy Dhingra
- St. Boniface Hospital Albrechtsen Research Centre, Institute of Cardiovascular Sciences, University of Manitoba, Winnipeg, MB, Canada
| | - Lorrie Kirshenbaum
- St. Boniface Hospital Albrechtsen Research Centre, Institute of Cardiovascular Sciences, University of Manitoba, Winnipeg, MB, Canada
| | - Belma Turan
- Departments of Biophysics, Ankara University Faculty of Medicine, Ankara, Turkey
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Agmatine modulates calcium handling in cardiomyocytes of hibernating ground squirrels through calcium-sensing receptor signaling. Cell Signal 2018; 51:1-12. [PMID: 30030121 DOI: 10.1016/j.cellsig.2018.07.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2018] [Revised: 07/12/2018] [Accepted: 07/13/2018] [Indexed: 11/20/2022]
Abstract
True hibernators are remarkable group of mammals whose hearts are resistant to such stressors as deep hypothermia, ischemia, arrhythmia. Capability of cardiac cells from hibernating species to effectively rule Ca2+ homeostasis during torpor is poorly studied. Better understanding of these mechanisms could allow to introduce new strategies for improvement the cardiac performance and may be useful for cardiovascular medicine. Here for the first time we have shown that the regulation of Ca2+ handling and thereby cardiomyocyte contractility by endogenous neurotransmitter agmatine occurs through the modulation of calcium-sensing receptor (CaSR). In isolated cardiocytes of hibernating ground squirrels generating stationary Ca2+ transients in the absence of actual myocellular excitation, low doses of this polyamine (up to 500 μM) induce the Gβγ-dependent activation of PI3-kinase with subsequent stimulation of Akt-kinase and nitric oxide (NO) production by endothelial NO-synthase (eNOS). NO production abolishes Ca2+ oscillations in virtue of the enhancement of Ca2+ reuptake by sarco(endo)plasmic Ca2+ ATPase (SERCA). Simultaneously, the activation of phospholipase A2 (PLA2) and arachidonic-acid dependent Ca2+ entry occur providing replenishment of Ca2+ store. High concentrations of agmatine (> 2 mM) induce other CaSR-mediated pathways involving phospholipase C (PLC) pathway, the formation of inositoltriphosphate (IP3) and diacylglicerol (DAG) followed by induction of their targets: IP3 receptors and protein kinase C isoforms (PKC), respectively. Furthermore, it is also responsible for the stimulation of PLA2 and elevation of intracellular calcium caused by arachidonic acid-regulated Ca2+-permeable (ARC) channels. Additionally, there is a potent store-operated Ca2+ entry (SOC) in cardiomyocyte. Negative (NPS 2143) and positive (R 568) allosteric modulators of CaSR recapitulate effects of low and high agmatine doses on Ca2+ handling and NO synthesis. These facts and the alteration of agmatine influence in response to an increase of extracellular Ca2+, which is the direct agonist of CaSR, may confirm the participation of CaSR in regulation of Ca2+ handling and excitability of cardiomyocytes by agmatine.
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Role of superoxide ion formation in hypothermia/rewarming induced contractile dysfunction in cardiomyocytes. Cryobiology 2018; 81:57-64. [PMID: 29458041 DOI: 10.1016/j.cryobiol.2018.02.010] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2017] [Revised: 02/12/2018] [Accepted: 02/13/2018] [Indexed: 01/24/2023]
Abstract
Rewarming following accidental hypothermia is associated with circulatory collapse due primarily to impaired cardiac contractile (systolic) function. Previously, we found that reduced myofilament Ca2+ sensitivity underlies hypothermia/rewarming (H/R)-induced cardiac contractile dysfunction. This reduced Ca2+ sensitivity is associated with troponin I (cTnI) phosphorylation. We hypothesize that H/R induces reactive oxygen species (ROS) formation in cardiomyocytes, which leads to cTnI phosphorylation and reduced myofilament Ca2+ sensitivity. To test this hypothesis, we exposed isolated rat cardiomyocytes to a 2-h period of severe hypothermia (15 °C) followed by rewarming (35 °C) with and without antioxidant (TEMPOL) treatment. Simultaneous measurements of cytosolic Ca2+ ([Ca2+]cyto) and contractile (sarcomere shortening) responses indicated that H/R-induced contractile dysfunction and reduced Ca2+ sensitivity was prevented in cardiomyocytes treated with TEMPOL. In addition, TEMPOL treatment blunted H/R-induced cTnI phosphorylation. These results support our overall hypothesis and suggest that H/R disrupts excitation-contraction coupling of the myocardium through a cascade of event triggered by excessive ROS formation during hypothermia. Antioxidant treatment may improve successful rescue of accidental hypothermia victims.
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Horii Y, Shiina T, Shimizu Y. The Mechanism Enabling Hibernation in Mammals. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2018; 1081:45-60. [PMID: 30288703 DOI: 10.1007/978-981-13-1244-1_3] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Some rodents including squirrels and hamsters undergo hibernation. During hibernation, body temperature drops to only a few degrees above ambient temperature. The suppression of whole-body energy expenditure is associated with regulated, but not passive, reduction of cellular metabolism. The heart retains the ability to beat constantly, although body temperature drops to less than 10 °C during hibernation. Cardiac myocytes of hibernating mammals are characterized by reduced Ca2+ entry into the cell membrane and a concomitant enhancement of Ca2+ release from and reuptake by the sarcoplasmic reticulum. These adaptive changes would help in preventing excessive Ca2+ entry and its overload and in maintaining the resting levels of intracellular Ca2+. Adaptive changes in gene expression in the heart prior to hibernation may be indispensable for acquiring cold resistance. In addition, protective effects of cold-shock proteins are thought to have an important role. We recently reported the unique expression pattern of cold-inducible RNA-binding protein (CIRP) in the hearts of hibernating hamsters. The CIRP mRNA is constitutively expressed in the heart of a nonhibernating euthermic hamster with several different forms probably due to alternative splicing. The short product contained the complete open reading frame for full-length CIRP, while the long product had inserted sequences containing a stop codon, suggesting production of a C-terminal deletion isoform of CIRP. In contrast to nonhibernating hamsters, only the short product was found in hibernating animals. Thus, these results indicate that CIRP expression in the hamster heart is regulated at the level of alternative splicing, which would permit a rapid increment of functional CIRP when entering hibernation. We will summarize the current understanding of the cold-resistant property of the heart in hibernating animals.
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Affiliation(s)
- Yuuki Horii
- Department of Basic Veterinary Science, Laboratory of Physiology, The United Graduate School of Veterinary Sciences, Gifu University, Gifu, Japan
| | - Takahiko Shiina
- Department of Basic Veterinary Science, Laboratory of Physiology, The United Graduate School of Veterinary Sciences, Gifu University, Gifu, Japan
| | - Yasutake Shimizu
- Department of Basic Veterinary Science, Laboratory of Physiology, The United Graduate School of Veterinary Sciences, Gifu University, Gifu, Japan.
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9
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Zhang Y, Storey KB. Regulation of gene expression by NFAT transcription factors in hibernating ground squirrels is dependent on the cellular environment. Cell Stress Chaperones 2016; 21:883-94. [PMID: 27344571 PMCID: PMC5003805 DOI: 10.1007/s12192-016-0713-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2016] [Revised: 05/30/2016] [Accepted: 06/13/2016] [Indexed: 12/22/2022] Open
Abstract
Calcineurin is a calmodulin-stimulated phosphatase that regulates the nuclear translocation of nuclear factor of activated T cell (NFAT) c1-4 through dephosphorylation. We believe that this mechanism plays various roles in the remodeling and maintenance of Ictidomys tridecemlineatus skeletal muscle. During hibernation, bouts of torpor and arousal take place, and squirrels do not lose muscle mass despite being inactive. Protein expression of Ca(2+) signaling proteins were studied using immunoblotting. A DNA-protein interaction ELISA technique was created to test the binding of NFATs in the nucleus to DNA probes containing the NFAT response element under environmental conditions reflective of those during hibernation. Calcineurin protein levels increased by 3.08-fold during torpor (compared to euthermic control), whereas calpain1 levels also rose by 3.66-fold during torpor. Calmodulin levels were elevated upon entering torpor. NFATc4 binding to DNA showed a 1.4-fold increase during torpor, and we found that this binding was further enhanced when 600 nM of Ca(2+) was supplemented. We also found that decreasing the temperature of ELISAs resulted in progressive decreases in the binding of NFATs c1, c3, and c4 to DNA. In summary, calmodulin and calpain1 appear to activate calcineurin and NFATc4 during torpor. NFAT binding to target promoters is affected by intranuclear [Ca(2+)] and environmental temperatures. Therefore, Ca(2+) signaling and temperature changes play key roles in regulation of the NFAT-calcineurin pathway in skeletal muscle of hibernating 13-lined ground squirrels over the torpor-arousal cycle, and they may contribute to the avoidance of disuse-induced muscle atrophy that occurs naturally in these animals.
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Affiliation(s)
- Yichi Zhang
- Institute of Biochemistry and Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON, K1S 5B6, Canada
| | - Kenneth B Storey
- Institute of Biochemistry and Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON, K1S 5B6, Canada.
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Schaible N, Han YS, Hoang T, Arteaga G, Tveita T, Sieck G. Hypothermia/rewarming disrupts excitation-contraction coupling in cardiomyocytes. Am J Physiol Heart Circ Physiol 2016; 310:H1533-40. [PMID: 26993227 DOI: 10.1152/ajpheart.00840.2015] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/03/2015] [Accepted: 03/16/2016] [Indexed: 12/25/2022]
Abstract
Hypothermia/rewarming (H/R) is poorly tolerated by the myocardium; however, the underlying intracellular basis of H/R-induced cardiac dysfunction remains elusive. We hypothesized that in cardiomyocytes, H/R disrupts excitation-contraction coupling by reducing myofilament Ca(2+) sensitivity due to an increase in cardiac troponin I (cTnI) phosphorylation. To test this hypothesis, isolated rat cardiomyocytes (13-15 cells from 6 rats per group) were electrically stimulated to evoke both cytosolic Ca(2+) ([Ca(2+)]cyto) and contractile (sarcomere shortening) responses that were simultaneously measured using an IonOptix system. Cardiomyocytes were divided into two groups: 1) those exposed to hypothermia (15°C for 2 h) followed by rewarming (35°C; H/R); or 2) time-matched normothermic (35°C) controls (CTL). Contractile dysfunction after H/R was indicated by reduced velocity and extent of sarcomere length (SL) shortening compared with time-matched controls. Throughout hypothermia, basal [Ca(2+)]cyto increased and the duration of evoked [Ca(2+)]cyto transients was prolonged. Phase-loop plots of [Ca(2+)]cyto vs. contraction were shifted rightward in cardiomyocytes during hypothermia compared with CTL, indicating a decrease in Ca(2+) sensitivity. Using Western blot, we found that H/R increases cTnI phosphorylation. These results support our overall hypothesis and suggest that H/R disrupts excitation-contraction coupling of cardiomyocytes due to increased cTnI phosphorylation and reduced Ca(2+) sensitivity.
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Affiliation(s)
- Niccole Schaible
- Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, Minnesota; and
| | - Young Soo Han
- Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, Minnesota; and
| | - Thuy Hoang
- Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, Minnesota; and
| | - Grace Arteaga
- Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, Minnesota; and
| | - Torkjel Tveita
- Departments of Anesthesiology and Physiology, University of Tromsø-The Arctic University of Norway, Tromsø, Norway
| | - Gary Sieck
- Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, Minnesota; and
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Electromagnetic fields instantaneously modulate nitric oxide signaling in challenged biological systems. Biochem Biophys Res Commun 2012; 426:330-3. [DOI: 10.1016/j.bbrc.2012.08.078] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2012] [Accepted: 08/15/2012] [Indexed: 11/20/2022]
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12
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Egorov YV, Glukhov AV, Efimov IR, Rosenshtraukh LV. Hypothermia-induced spatially discordant action potential duration alternans and arrhythmogenesis in nonhibernating versus hibernating mammals. Am J Physiol Heart Circ Physiol 2012; 303:H1035-46. [PMID: 22886418 DOI: 10.1152/ajpheart.00786.2011] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The heart of hibernating species is resistant to lethal ventricular fibrillation (VF) induced by hypothermia. Spatially discordant (SDA) cardiac alternans is a promising predictor of VF, yet its role in the mechanism of hypothermic arrhythmogenesis in both nonhibernating and hibernating mammals remains unclear. We optically mapped the posterior epicardial surface of Langendorff-perfused hearts of winter hibernating (WH, n = 13), interbout arousal (IBA; n = 4), and summer active (SA, n = 6) ground squirrels (GSs; Spermophilus undulatus) and rabbits (n = 10). Action potential duration (APD) and conduction velocity (CV) dynamic restitution and alternans were determined at 37 to 17°C. In all animals, hypothermia induced heterogeneous APD prolongation, enhanced APD dispersion, and slowed CV. In all groups, hypothermia promoted the formation of APD alternans, which was predominantly spatially concordant in GSs and SDA in rabbits (SD of APD dispersion: 4.2 ± 0.4% vs. 2.0 ± 0.3% at 37°C and 7.5 ± 1.1% vs. 3.4 ± 0.5% at 17°C, P < 0.001 for rabbits vs. the WH group, respectively). In rabbits, hypothermia significantly increased the magnitude of SDA, which enhanced the ventricular repolarization gradient, caused conduction delays (CV: 3.2 vs. 8.2 cm/s at 17°C in rabbits vs. the WH group), conduction block, and the onset of VF (0% at 37°C vs. 60% at 17°C, P < 0.01). In contrast, no arrhythmia was observed in GS hearts at any temperature. The amplitude of CV alternans was greater in rabbits (5.2 ± 0.4% versus 4.5 ± 0.3% at 37°C and 35.3 ± 4.2% vs. 14.9 ± 1.5% at 17°C in rabbits vs. the WH group, P < 0.001 at 17°C) and correlated with the amplitude of SDA. In conclusion, the mechanism underlying SDA formation during hypothermia is likely associated with CV alternans conditioned by an enhanced dispersion of repolarization. The factors of hibernating species resistance to SDA and VF seem to be the safe and dynamically stable conduction and the low dispersion of repolarization.
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Affiliation(s)
- Yuriy V Egorov
- Laboratory of Heart Electrophysiology, Cardiology Research Center, Moscow 121552, Russia
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13
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Hughey CC, Alfaro MP, Belke DD, Rottman JN, Young PP, Wasserman DH, Shearer J. Increased oxygen consumption and OXPHOS potential in superhealer mesenchymal stem cells. CELL REGENERATION 2012; 1:3. [PMID: 25408866 DOI: 10.1186/2045-9769-1-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2011] [Accepted: 06/28/2012] [Indexed: 01/16/2023]
Abstract
BACKGROUND Cell-based therapies show promise in repairing cardiac tissue and improving contractile performance following a myocardial infarction. Despite this, ischemia-induced death of transplanted cells remains a major hurdle to the efficacy of treatment. 'Superhealer' MRL/MpJ mesenchymal stem cells (MRL-MSCs) have been reported to exhibit increased engraftment resulting in reduced infarct size and enhanced contractile function. This study determines whether intrinsic differences in mitochondrial oxidative phosphorylation (OXPHOS) assist in explaining the enhanced cellular survival and engraftment of MRL-MSCs. FINDINGS Compared to wild type MSCs (WT-MSCs), mitochondria from intact MRL-MSCs exhibited an increase in routine respiration and maximal electron transport capacity by 2.0- and 3.5-fold, respectively. When routine oxygen utilization is expressed as a portion of maximal cellular oxygen flux, the MRL-MSCs have a greater spare respiratory capcity. Additionally, glutamate/malate succinate-supported oxygen consumption in permeabilized cells was elevated approximately 1.25- and 1.4-fold in the MRL-MSCs, respectively. CONCLUSION The results from intact and permeabilized MSCs indicate MRL-MSCs exhibit a greater reliance on and capacity for aerobic metabolism. The greater capacity for oxidative metabolism may provide a protective effect by increasing ATP synthesis per unit substrate and prevent glycolysis-mediated acidosis and subsequent cell death upon transplantation into the glucose-and oxygen-deprived environment of the infarcted heart.
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Affiliation(s)
- Curtis C Hughey
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Calgary, Calgary, AB T2N 1N4 Canada ; University of Calgary, KNB Rm 3318. 2500 University Dr. NW, Calgary, Alberta Canada T2N 1N4
| | - Maria P Alfaro
- Department of Pathology, School of Medicine, Vanderbilt University, Nashville, 37232 TN USA
| | - Darrell D Belke
- Faculty of Kinesiology, University of Calgary, Calgary, AB T2N 1N4 Canada
| | - Jeffery N Rottman
- Department of Medicine, Division of Cardiovascular Medicine, School of Medicine, Vanderbilt University, Nashville, 37240 TN USA
| | - Pampee P Young
- Department of Pathology, School of Medicine, Vanderbilt University, Nashville, 37232 TN USA ; Department of Veterans Affairs Medical Center, Nashville, 37232 TN USA
| | - David H Wasserman
- Department of Molecular Physiology and Biophysics, School of Medicine, Vanderbilt University, Nashville, 37240 TN USA
| | - Jane Shearer
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Calgary, Calgary, AB T2N 1N4 Canada ; Faculty of Kinesiology, University of Calgary, Calgary, AB T2N 1N4 Canada
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Pilla A, Fitzsimmons R, Muehsam D, Wu J, Rohde C, Casper D. Electromagnetic fields as first messenger in biological signaling: Application to calmodulin-dependent signaling in tissue repair. Biochim Biophys Acta Gen Subj 2011; 1810:1236-45. [PMID: 22005645 DOI: 10.1016/j.bbagen.2011.10.001] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2011] [Revised: 09/21/2011] [Accepted: 10/01/2011] [Indexed: 01/01/2023]
Abstract
BACKGROUND The transduction mechanism for non-thermal electromagnetic field (EMF) bioeffects has not been fully elucidated. This study proposes that an EMF can act as a first messenger in the calmodulin-dependent signaling pathways that orchestrate the release of cytokines and growth factors in normal cellular responses to physical and/or chemical insults. METHODS Given knowledge of Ca(2+) binding kinetics to calmodulin (CaM), an EMF signal having pulse duration or carrier period shorter than bound Ca(2+) lifetime may be configured to accelerate binding, and be detectable above thermal noise. New EMF signals were configured to modulate calmodulin-dependent signaling and assessed for efficacy in cellular studies. RESULTS Configured EMF signals modulated CaM-dependent enzyme kinetics, produced several-fold increases in key second messengers to include nitric oxide and cyclic guanosine monophosphate in chondrocyte and endothelial cultures and cyclic adenosine monophosphate in neuronal cultures. Calmodulin antagonists and downstream blockers annihilated these effects, providing strong support for the proposed mechanism. CONCLUSIONS Knowledge of the kinetics of Ca(2+) binding to CaM, or for any ion binding specific to any signaling cascade, allows the use of an electrochemical model by which the ability of any EMF signal to modulate CaM-dependent signaling can be assessed a priori or a posteriori. Results are consistent with the proposed mechanism, and strongly support the Ca/CaM/NO pathway as a primary EMF transduction pathway. GENERAL SIGNIFICANCE The predictions of the proposed model open a host of significant possibilities for configuration of non-thermal EMF signals for clinical and wellness applications that can reach far beyond fracture repair and wound healing.
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Affiliation(s)
- Arthur Pilla
- Departments of Biomedical Engineering, Columbia University and Orthopedics, Mount Sinai School of Medicine, New York, NY, United States.
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15
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Tveita T, Sieck GC. The physiologic responses to epinephrine during cooling and after rewarming in vivo. CRITICAL CARE : THE OFFICIAL JOURNAL OF THE CRITICAL CARE FORUM 2011; 15:R225. [PMID: 21943089 PMCID: PMC3334771 DOI: 10.1186/cc10465] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/08/2011] [Revised: 08/12/2011] [Accepted: 09/23/2011] [Indexed: 11/12/2022]
Abstract
Introduction The purpose of our study was to determine whether hypothermia has any effects on physiological hemodynamic responses to epinephrine (Epi), and whether rewarming reverses these effects. Methods Sprague-Dawley rats were instrumented to measure mean arterial pressure (MAP), and left ventricular (LV) pressure-volume changes were recorded by using a Millar pressure-volume conductance catheter. Core temperature was reduced from 37°C to 28°C and returned to 37°C by using both internal and external heat exchangers. Two groups of rats were infused with either saline (n = 7), or Epi 0.125 μg/min continuously (n = 7). At 33°C, 30°C, and 28°C, the Epi infusion was temporarily increased from 0.125 to 1.25 μg/min. Results Before cooling, Epi infusion in both groups resulted in a significant, dose-dependent increase in heart rate (HR), stroke volume (SV), cardiac output (CO), LV dP/dtmax (maximum derivative of systolic pressure over time), but only Epi infusion at 1.25 μg/min caused elevation of MAP. During cooling to 30°C, Epi infusion at 0.125 μg/min caused a significant elevation of central hemodynamic variables, whereas MAP remained unchanged. In contrast, Epi infusions at 1.25 μg/min caused a significant elevation of MAP during cooling to 28°C but no increases in central hemodynamics. After rewarming, all hemodynamic variables returned to baseline in both groups, but only the saline-treated animals displayed the prehypothermic hemodynamic dose responses to Epi infusions. Conclusions This study shows that hypothermia causes a change in the physiological hemodynamic response to Epi, which is not reversed by rewarming.
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Affiliation(s)
- Torkjel Tveita
- Department of Physiology & Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA
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16
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Khaliulin I, Halestrap AP, Suleiman MS. Temperature preconditioning is optimal at 26° C and confers additional protection to hypothermic cardioplegic ischemic arrest. Exp Biol Med (Maywood) 2011; 236:736-45. [PMID: 21606118 PMCID: PMC3125701 DOI: 10.1258/ebm.2011.010357] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We have recently shown that brief episodes of hypothermic perfusion interspersed with periods of normothermic perfusion, referred to as temperature preconditioning (TP), are cardioprotective and can be mimicked by consecutive isoproterenol/adenosine treatment. Here we investigate the optimal temperature for TP and whether TP further enhances protection provided by hypothermic ischemia with or without polarized cardioplegic arrest. Three experimental groups of Langendorff-perfused rat hearts were used. In the first group, hearts were subjected to three episodes of hypothermic perfusion at 7, 17, 26 and 32°C during the TP protocol, followed by 30 min normothermic index ischemia and 60 min reperfusion (37°C). Protein kinase A (PKA) activity and cyclic AMP (cAMP) concentrations were measured prior to index ischemia. In the second group, TP (26°C) hearts were subjected to two hours hypothermic index ischemia at 26°C and two hours normothermic reperfusion. In the third group, TP (26°C) hearts or hearts treated with isoproterenol/adenosine (pharmacological simulation of TP) were subjected to four hours hypothermic index ischemia with procaine-induced polarized cardioplegia at 26°C followed by two hours normothermic reperfusion. Hemodynamic function recovery, lactate dehydrogenase release and infarct size were used to assess cardioprotection. TP at 26°C resulted in highest cardioprotection, increased cAMP concentration and PKA activity, while TP at 7°C exacerbated ischemia/reperfusion damage, and had no effect on cAMP concentration or PKA activity. TP at 26°C also protected hearts during hypothermic ischemia with or without polarized cardioplegia. Isoproterenol/adenosine treatment conferred additional protection similar to TP. In conclusion, the study shows that TP-induced cardioprotection is temperature dependent and is optimal at 26°C; TP confers additional protection to hypothermia and polarized cardioplegia; and that the pharmacological treatment based on the mechanism of TP (consecutive isoproterenol/adenosine treatment) is a potential cardioprotective strategy that can be used during heart surgery and transplantation.
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Affiliation(s)
- Igor Khaliulin
- School of Biochemistry and the Bristol Heart Institute, Medical Sciences Building, University of Bristol, University Walk, Bristol, UK.
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17
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Han YS, Tveita T, Prakash YS, Sieck GC. Mechanisms underlying hypothermia-induced cardiac contractile dysfunction. Am J Physiol Heart Circ Physiol 2010; 298:H890-7. [PMID: 20023122 PMCID: PMC7938765 DOI: 10.1152/ajpheart.00805.2009] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/25/2009] [Accepted: 12/14/2009] [Indexed: 11/22/2022]
Abstract
Rewarming patients after profound hypothermia may result in acute heart failure and high mortality (50-80%). However, the underlying pathophysiological mechanisms are largely unknown. We characterized cardiac contractile function in the temperature range of 15-30 degrees C by measuring the intracellular Ca(2+) concentration ([Ca(2+)](i)) and twitch force in intact left ventricular rat papillary muscles. Muscle preparations were loaded with fura-2 AM and electrically stimulated during cooling at 15 degrees C for 1.5 h before being rewarmed to the baseline temperature of 30 degrees C. After hypothermia/rewarming, peak twitch force decreased by 30-40%, but [Ca(2+)](i) was not significantly altered. In addition, we assessed the maximal Ca(2+)-activated force (F(max)) and Ca(2+) sensitivity of force in skinned papillary muscle fibers. F(max) was decreased by approximately 30%, whereas the pCa required for 50% of F(max) was reduced by approximately 0.14. In rewarmed papillary muscle, both total cardiac troponin I (cTnI) phosphorylation and PKA-mediated cTnI phosphorylation at Ser23/24 were significantly increased compared with controls. We conclude that after hypothermia/rewarming, myocardial contractility is significantly reduced, as evidenced by reduced twitch force and F(max). The reduced myocardial contractility is attributed to decreased Ca(2+) sensitivity of force rather than [Ca(2+)](i) itself, resulting from increased cTnI phosphorylation.
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Affiliation(s)
- Young-Soo Han
- Dept. of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
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18
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Kondratiev TV, Wold RM, Aasum E, Tveita T. Myocardial mechanical dysfunction and calcium overload following rewarming from experimental hypothermia in vivo. Cryobiology 2008; 56:15-21. [DOI: 10.1016/j.cryobiol.2007.09.005] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2007] [Revised: 09/12/2007] [Accepted: 09/19/2007] [Indexed: 11/27/2022]
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19
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Camara AKS, Aldakkak M, Heisner JS, Rhodes SS, Riess ML, An J, Heinen A, Stowe DF. ROS scavenging before 27 degrees C ischemia protects hearts and reduces mitochondrial ROS, Ca2+ overload, and changes in redox state. Am J Physiol Cell Physiol 2007; 292:C2021-31. [PMID: 17287367 DOI: 10.1152/ajpcell.00231.2006] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have shown that cold perfusion of hearts generates reactive oxygen and nitrogen species (ROS/RNS). In this study, we determined 1) whether ROS scavenging only during cold perfusion before global ischemia improves mitochondrial and myocardial function, and 2) which ROS leads to compromised cardiac function during ischemia and reperfusion (I/R) injury. Using fluorescence spectrophotometry, we monitored redox balance (NADH and FAD), O(2)(*-) levels and mitochondrial Ca(2+) (m[Ca(2+)]) at the left ventricular wall in 120 guinea pig isolated hearts divided into control (Con), MnTBAP (a superoxide dismutase 2 mimetic), MnTBAP (M) + catalase (C) + glutathione (G) (MCG), C+G (CG), and N(G)-nitro-L-arginine methyl ester (L-NAME; a nitric oxide synthase inhibitor) groups. After an initial period of warm perfusion, hearts were treated with drugs before and after at 27 degrees C. Drugs were washed out before 2 h at 27 degrees C ischemia and 2 h at 37 degrees C reperfusion. We found that on reperfusion the MnTBAP group had the worst functional recovery and largest infarction with the highest m[Ca(2+)], most oxidized redox state and increased ROS levels. The MCG group had the best recovery, the smallest infarction, the lowest ROS level, the lowest m[Ca(2+)], and the most reduced redox state. CG and L-NAME groups gave results intermediate to those of the MnTBAP and MCG groups. Our results indicate that the scavenging of cold-induced O(2)(*-) species to less toxic downstream products additionally protects during and after cold I/R by preserving mitochondrial function. Because MnTBAP treatment showed the worst functional return along with poor preservation of mitochondrial bioenergetics, accumulation of H(2)O(2) and/or hydroxyl radicals during cold perfusion may be involved in compromised function during subsequent cold I/R injury.
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Affiliation(s)
- Amadou K S Camara
- Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, WI 53226, USA
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20
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Belke DD, Swanson E, Suarez J, Scott BT, Stenbit AE, Dillmann WH. Increased expression of SERCA in the hearts of transgenic mice results in increased oxidation of glucose. Am J Physiol Heart Circ Physiol 2006; 292:H1755-63. [PMID: 17142343 DOI: 10.1152/ajpheart.00884.2006] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
While several transgenic mouse models exhibit improved contractile characteristics in the heart, less is known about how these changes influence energy metabolism, specifically the balance between carbohydrate and fatty acid oxidation. In the present study we examine glucose and fatty acid oxidation in transgenic mice, generated to overexpress sarco(endo)plasmic reticulum calcium-ATPase (SERCA), which have an enhanced contractile phenotype. Energy substrate metabolism was measured in isolated working hearts using radiolabeled glucose and palmitate. We also examined oxygen consumption to see whether SERCA overexpression is associated with increased oxygen utilization. Since SERCA is important in calcium handling within the cardiac myocyte, we examined cytosolic calcium transients in isolated myocytes using indo-1, and mitochondrial calcium levels using pericam, an adenovirally expressed, mitochondrially targeted ratiometric calcium indicator. Oxygen consumption did not differ between wild-type and SERCA groups; however, we were able to show an increased utilization of glucose for oxidative metabolism and a corresponding decreased utilization of fatty acids in the SERCA group. Cytosolic calcium transients were increased in myocytes isolated from SERCA mice, and they show a faster rate of decay of the calcium transient. With these observations we noted increased levels of mitochondrial calcium in the SERCA group, which was associated with an increase in the active form of the pyruvate dehydrogenase complex. Since an increase in mitochondrial calcium levels leads to activation of the pyruvate dehydrogenase complex (the rate-limiting step for carbohydrate oxidation), the increased glucose utilization observed in isolated perfused hearts in the SERCA group may reflect a higher level of mitochondrial calcium.
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Affiliation(s)
- Darrell D Belke
- Department of Medicine, University of California, San Diego, La Jolla, California 92093-0618, USA
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21
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Fu Y, Zhang GQ, Hao XM, Wu CH, Chai Z, Wang SQ. Temperature dependence and thermodynamic properties of Ca2+ sparks in rat cardiomyocytes. Biophys J 2005; 89:2533-41. [PMID: 16113119 PMCID: PMC1366752 DOI: 10.1529/biophysj.105.067074] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
To elucidate the temperature dependence and underlying thermodynamic determinants of the elementary Ca2+ release from the sarcoplasmic reticulum, we characterized Ca2+ sparks originating from ryanodine receptors (RyRs) in rat cardiomyocytes over a wide range of temperature. From 35 degrees C to 10 degrees C, the normalized fluo-3 fluorescence of Ca2+ sparks decreased monotonically, but the Delta[Ca2+]i were relatively unchanged due to increased resting [Ca2+]i. The time-to-peak of Ca2+ sparks, which represents the RyR Ca2+ release duration, was prolonged by 37% from 35 degrees C to 10 degrees C. An Arrhenius plot of the data identified a jump of apparent activation energy from 5.2 to 14.6 kJ/mol at 24.8 degrees C, which presumably reflects a transition of sarcoplasmic reticulum lipids. Thermodynamic analysis of the decay kinetics showed that active transport plays little role in early recovery but a significant role in late recovery of local Ca2+ concentration. These results provided a basis for quantitative interpretation of intracellular Ca2+ signaling under various thermal conditions. The relative temperature insensitivity above the transitional 25 degrees C led to the notion that Ca2+ sparks measured at a "warm room" temperature are basically acceptable in elucidating mammalian heart function.
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Affiliation(s)
- Yu Fu
- National Key Laboratory of Biomembrane and Membrane Biotechnology, College of Life Sciences, Peking University, Beijing 100871, China
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22
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Moopanar TR, Allen DG. Reactive oxygen species reduce myofibrillar Ca2+ sensitivity in fatiguing mouse skeletal muscle at 37 degrees C. J Physiol 2005; 564:189-99. [PMID: 15718257 PMCID: PMC1456045 DOI: 10.1113/jphysiol.2005.083519] [Citation(s) in RCA: 117] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The mechanisms of muscle fatigue were studied in small muscle bundles and single fibres isolated from the flexor digitorum brevis of the mouse. Fatigue caused by repeated isometric tetani was accelerated at body temperature (37 degrees C) when compared to room temperature (22 degrees C). The membrane-permeant reactive oxygen species (ROS) scavenger, Tiron (5 mM), had no effect on the rate of fatigue at 22 degrees C but slowed the rate of fatigue at 37 degrees C to that observed at 22 degrees C. Single fibres were microinjected with indo-1 to measure intracellular calcium. In the accelerated fatigue at 37 degrees C the tetanic [Ca2+](i) did not change significantly and the decline of maximum Ca2+-activated force was similar to that observed at 22 degrees C. The cause of the greater rate of fatigue at 37 degrees C was a large fall in myofibrillar Ca2+ sensitivity. In the presence of Tiron, the large fall in Ca2+ sensitivity was abolished and the usual decline in tetanic [Ca2+](i) was observed. This study confirms the importance of ROS in fatigue at 37 degrees C and shows that the mechanism of action of ROS is a decline in myofibrillar Ca2+ sensitivity.
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Affiliation(s)
- Terence R Moopanar
- Institute for Biomedical Sciences, School of Medical Sciences, University of Sydney F13, NSW 2006, Australia
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23
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Rhodes SS, Ropella KM, Audi SH, Camara AKS, Kevin LG, Pagel PS, Stowe DF. Cross-bridge kinetics modeled from myoplasmic [Ca2+] and LV pressure at 17 degrees C and after 37 degrees C and 17 degrees C ischemia. Am J Physiol Heart Circ Physiol 2003; 284:H1217-29. [PMID: 12531735 DOI: 10.1152/ajpheart.00816.2002] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We modeled changes in contractile element kinetics derived from the cyclic relationship between myoplasmic [Ca(2+)], measured by indo 1 fluorescence, and left ventricular pressure (LVP). We estimated model rate constants of the Ca(2+) affinity for troponin C (TnC) on actin (A) filament (TnCA) and actin and myosin (M) cross-bridge (A x M) cycling in intact guinea pig hearts during baseline 37 degrees C perfusion and evaluated changes at 1) 20 min 17 degrees C pressure, 2) 30-min reperfusion (RP) after 30-min 37 degrees C global ischemia during 37 degrees C RP, and 3) 30-min RP after 240-min 17 degrees C global ischemia during 37 degrees C RP. At 17 degrees C perfusion versus 37 degrees C perfusion, the model predicted: A x M binding was less sensitive; A x M dissociation was slower; Ca(2+) was less likely to bind to TnCA with A x M present; and Ca(2+) and TnCA binding was less sensitive in the absence of A x M. Model results were consistent with a cold-induced fall in heart rate from 260 beats/min (37 degrees C) to 33 beats/min (17 degrees C), increased diastolic LVP, and increased phasic Ca(2+). On RP after 37 degrees C ischemia vs. 37 degrees C perfusion, the model predicted the following: A x M binding was less sensitive; A x M dissociation was slower; and Ca(2+) was less likely to bind to TnCA in the absence of A. M. Model results were consistent with reduced myofilament responsiveness to [Ca(2+)] and diastolic contracture on 37 degrees C RP. In contrast, after cold ischemia versus 37 degrees C perfusion, A x M association and dissociation rates, and Ca(2+) and TnCA association rates, returned to preischemic values, whereas the dissociation rate of Ca(2+) from A x M was ninefold faster. This cardiac muscle kinetic model predicted a better-restored relationship between Ca(2+) and cross-bridge function on RP after an eightfold longer period of 17 degrees C than 37 degrees C ischemia.
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Affiliation(s)
- Samhita S Rhodes
- Department of Biomedical Engineering, Marquette University, Milwaukee 53233, USA
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24
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Shiels HA, Vornanen M, Farrell AP. Effects of temperature on intracellular [Ca2+] in trout atrial myocytes. J Exp Biol 2002; 205:3641-50. [PMID: 12409490 DOI: 10.1242/jeb.205.23.3641] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARYAcute temperature change can be cardioplegic to mammals, yet certain ectotherms maintain their cardiac scope over a wide temperature range. To better understand the acute effects of temperature on the ectothermic heart,we investigated the stimulus-induced change in intracellular Ca2+concentration ([Ca2+]i; cytosolic Ca2+transient) in isolated rainbow trout myocytes at 7°C, 14°C and 21°C. Myocytes were voltage-clamped and loaded with Fura-2 to measure the L-type Ca2+ channel current (ICa) and[Ca2+]i during physiological action potential (AP)pulses at frequencies that correspond to trout heart rates in vivo at 7°C, 14°C and 21°C. Additionally, [Ca2+]iand ICa were examined with square (SQ) pulses at slow (0.2 Hz) and physiologically relevant contraction frequencies. The amplitude of[Ca2+]i decreased with increasing temperature for both SQ and AP pulses, which may contribute to the well-known negative inotropic effect of warm temperature on contractile strength in trout hearts. With SQ pulses, [Ca2+]i decreased from 474±53 nmol l-1 at 7°C to 198±21 nmol l-1 at 21°C,while the decrease in [Ca2+]i with AP pulses was from 234±49 nmol l-1 to 79±12 nmol l-1,respectively. Sarcolemmal Ca2+ influx was increased slightly at cold temperatures with AP pulses (charge transfer was 0.27±0.04 pC pF-1, 0.19±0.03 pC pF-1 and 0.13±0.03 pC pF-1 at 7°C, 14°C and 21°C, respectively). At all temperatures, cells were better able to maintain diastolic Ca2+levels at physiological frequencies with AP pulses compared with 500 ms SQ pulses. We suggest that temperature-dependent modulation of the AP is important for cellular Ca2+ regulation during temperature and frequency change in rainbow trout heart.
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Affiliation(s)
- Holly A Shiels
- Simon Fraser University, Biological Sciences, Burnaby, British Columbia, V5A 1S6, Canada.
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25
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Gilbert NF, Meyer PE, Tauriainen MP, Chao RY, Patel JB, Malloy CR, Jessen ME. Effects of hypothermia on myocardial substrate selection. Ann Thorac Surg 2002; 74:1208-12. [PMID: 12400770 DOI: 10.1016/s0003-4975(02)03873-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
BACKGROUND Hypothermia lowers the metabolic rate and increases ischemic tolerance but the effects of temperature on myocardial substrate selection are not well defined. METHODS Isolated rat hearts were perfused with physiologic concentrations of 13C labeled lactate, pyruvate, acetoacetate, mixed long-chain fatty acids, and glucose. Hearts were cooled over 5 to 10 minutes to one of four target temperatures (37 degrees, 32 degrees, 27 degrees, or 17 degrees C), then perfused for an additional 30 minutes, freeze-clamped, and extracted. 13C NMR spectra were obtained and substrate oxidation patterns were determined by isotopomer analysis. RESULTS Although hearts in all groups were supplied with identical substrates, the percentage of acetyl-CoA oxidized within the citric acid cycle that arose from fatty acids decreased significantly from 53.8% +/- 0.8% in the 37 degrees C group to 33.1% +/- 3.3% in the 17 degrees C group. Lactate or pyruvate utilization increased from 3.3% +/- 0.5% to 25.7% +/- 3.6%, respectively (p < 0.05 by one-way ANOVA). CONCLUSIONS These data suggest that moderate hypothermia suppresses fatty acid oxidation and deep hypothermia significantly increases utilization of lactate and pyruvate. These effects may result from relative inhibition of catabolism of complex molecules such as fatty acids, or stimulation of pyruvate dehydrogenase. These effects on substrate metabolism may play a role in myocardial protection afforded by hypothermia.
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Affiliation(s)
- Nathan F Gilbert
- Department of Cardiovascular and Thoracic Surgery, University of Texas Southwestern Medical Center at Dallas, 75390-8879, USA
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26
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Wang SQ, Lakatta EG, Cheng H, Zhou ZQ. Adaptive mechanisms of intracellular calcium homeostasis in mammalian hibernators. J Exp Biol 2002; 205:2957-62. [PMID: 12200399 DOI: 10.1242/jeb.205.19.2957] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
SUMMARYIntracellular Ca2+ homeostasis is a prerequisite for a healthy cell life. While cells from some mammals may suffer dysregulation of intracellular Ca2+ levels under certain deleterious and stressful conditions, including hypothermia and ischemia, cells from mammalian hibernators exhibit a remarkable ability to maintain a homeostatic intracellular Ca2+ environment. Compared with cells from non-hibernators, hibernator cells are characterized by downregulation of the activity of Ca2+ channels in the cell membrane, which helps to prevent excessive Ca2+ entry. Concomitantly, sequestration of Ca2+ by intracellular Ca2+ stores, especially the sarcoplasmic/endoplasmic reticulum, is enhanced to keep the resting levels of intracellular Ca2+ stable. An increase in stored Ca2+ in heart cells during hibernation ensures that the levels of Ca2+messenger are sufficient for forceful cell contraction under conditions of hypothermia. Maintenance of Na+ gradients, viaNa+—Ca2+ exchangers, is also important in the Ca2+ homeostasis of hibernator cells. Understanding the adaptive mechanisms of Ca2+ regulation in hibernating mammals may suggest new strategies to protect nonhibernator cells, including those of humans, from Ca2+-induced dysfunction.
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Affiliation(s)
- Shi Qiang Wang
- National Laboratory of Biomembrane and Membrane Biotechnology, College of Life Sciences, Peking University, Beijing 100871, China.
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Nakae Y, Fujita S, Namiki A. Isoproterenol enhances myofilament Ca(2+) sensitivity during hypothermia in isolated guinea pig beating hearts. Anesth Analg 2001; 93:846-52. [PMID: 11574344 DOI: 10.1097/00000539-200110000-00009] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
UNLABELLED Isoproterenol is often required to treat acute left ventricular dysfunction during separation from cardiopulmonary bypass for cardiac surgery. We hypothesized that heart rate and intracellular Ca(2+) concentration ([Ca(2+)]i) homeostasis may be important factors when isoproterenol improves the cardiac function during hypothermia. Accordingly, we investigated the effect of isoproterenol on the cardiac functional variables, [Ca(2+)]i, and myofilament Ca(2+) sensitivity under spontaneous beating during hypothermia. Intact guinea pig hearts were perfused with a modified Krebs-Ringer solution (baseline) and Krebs-Ringer solution containing isoproterenol (1 nM) at 37 degrees C, 32 degrees C, and 27 degrees C while all cardiac variables and [Ca(2+)]i were recorded. Isoproterenol increased developed left ventricular pressure (LVP), maximum rate of increase in LVP, and coronary inflow at 27 degrees C, and it also increased heart rate and maximum rate of decrease in LVP at each temperature (P < 0.05). Isoproterenol produced a leftward shift of the curve of developed LVP as a function of available [Ca(2+)]i at 32 degrees C and 27 degrees C (P < 0.05), without changing available [Ca(2+)]i. Isoproterenol improves the cardiac function, especially systolic ventricular function, by enhancement of myofilament Ca(2+) sensitivity under spontaneous beating during hypothermia in intact guinea pig hearts. IMPLICATIONS Enhancement of myofilament Ca(2+) sensitivity is involved in the improvement of cardiac function by isoproterenol under spontaneous beating during hypothermia.
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Affiliation(s)
- Y Nakae
- Department of Anesthesiology, Sapporo Medical University School of Medicine, Sapporo, Japan.
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Souza MM, Boyle RT. A moderate decrease in temperature inhibits the calcium signaling mechanism(s) of the regulatory volume decrease in chick embryo cardiomyocytes. Braz J Med Biol Res 2001; 34:137-41. [PMID: 11151040 DOI: 10.1590/s0100-879x2001000100018] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Chick cardiomyocytes, when submitted to hyposmotic swelling, exhibit a partial regulatory volume decrease (RVD). A Ca2+ influx by stretch-activated channels signals a taurine efflux and the RVD at 37 degrees C. We evaluated the cell's performance at room temperature. Cardiomyocytes isolated and cultured from 11-day-old chick embryos were submitted to a hyposmotic solution (180 mOsm/kg H2O) at 37 degrees C and at room temperature (26 degrees C). Under these conditions we measured the changes in cell volume as well as the intracellular free Ca2+ (using fura-2). During hyposmotic swelling, cells at 37 degrees C displayed a peak relative volume of 1.61 +/- 0.03 and recovery to 1.22 +/- 0.04 (N = 14), while cells at 26 degrees C presented a peak swell relative volume of 1.74 +/- 0.06 and did not recover (1.59 +/- 0.09, N = 9). Transient increases in intracellular Ca2+, which are characteristic of the normal RVD, were observed at both temperatures (29.1 +/- 4.5% (N = 8) and 115.2 +/- 42.8% (N = 5) increase at 37 degrees and 26 degrees C (P<0.05), respectively). A delay in the Ca2+ transient increase was also observed when the cells were at 26 degrees C (109 +/- 34 s compared to 38 +/- 9 s at 37 degrees C, P<0.05). At room temperature the RVD does not occur because the calcium transient increase, which is an early event in the signaling of the RVD, is delayed. Also, free calcium is not cleared as in the 37 degrees C RVD. In the normal RVD the free calcium returns to baseline levels. The very high and persistent free calcium levels seen at room temperature can lead to unregulated enzyme activities and may promote irreversible injury and cell death.
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Affiliation(s)
- M M Souza
- Department of Cell Biology, Duke University Medical Center, Durham, NC, USA.
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Stowe DF, Varadarajan SG, An J, Smart SC. Reduced cytosolic Ca(2+) loading and improved cardiac function after cardioplegic cold storage of guinea pig isolated hearts. Circulation 2000; 102:1172-7. [PMID: 10973848 DOI: 10.1161/01.cir.102.10.1172] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Hypothermia is cardioprotective, but it causes Ca(2+) loading and reduced function on rewarming. The aim was to associate changes in cytosolic Ca(2+) with function in intact hearts before, during, and after cold storage with or without cardioplegia (CP). METHODS AND RESULTS Guinea pig hearts were initially perfused at 37 degrees C with Krebs-Ringer's (KR) solution (in mmol/L: Ca(2+) 2.5, K(+) 5, Mg(2+) 2.4). One group was perfused with CP solution (Ca(2+) 2.5, K(+) 18, Mg(2+) 7.2) during cooling and storage at 3 degrees C for 4 hours; another was perfused with KR. LV pressure (LVP), dP/dt, O(2) consumption, and cardiac efficiency were monitored. Cytosolic phasic [Ca(2+)] was calculated from indo 1 fluorescence signals obtained at the LV free wall. Cooling with KR increased diastolic and phasic [Ca(2+)], whereas cooling with CP suppressed phasic [Ca(2+)] and reduced the rise in diastolic [Ca(2+)]. Reperfusion with warm KR increased phasic [Ca(2+)] 86% more after CP at 20 minutes and did not increase diastolic [Ca(2+)] at 60 minutes, compared with a 20% increase in phasic [Ca(2+)] after KR. During early and later reperfusion after CP, there was a 126% and 50% better return of LVP than after KR; during later reperfusion, O(2) consumption was 23% higher and cardiac efficiency was 38% higher after CP than after KR. CONCLUSIONS CP decreases the rise in cardiac diastolic [Ca(2+)] observed during cold storage in KR. Decreased diastolic [Ca(2+)] and increased systolic [Ca(2+)] after CP improves function on reperfusion because of reduced Ca(2+) loading during and immediately after cold CP storage.
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Affiliation(s)
- D F Stowe
- Anesthesiology Research Laboratory, Department of Anesthesiology, Medical College of Wisconsin, and Veterans Affairs Medical Center, Milwaukee, WI,
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Oliver AE, Baker GA, Fugate RD, Tablin F, Crowe JH. Effects of temperature on calcium-sensitive fluorescent probes. Biophys J 2000; 78:2116-26. [PMID: 10733989 PMCID: PMC1300803 DOI: 10.1016/s0006-3495(00)76758-0] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
The effect of temperature on the binding equilibria of calcium-sensing dyes has been extensively studied, but there are also important temperature-related changes in the photophysics of the dyes that have been largely ignored. We conducted a systematic study of thermal effects on five calcium-sensing dyes under calcium-saturated and calcium-free conditions. Quin-2, chlortetracycline, calcium green dextran, Indo-1, and Fura-2 all show temperature-dependent effects on fluorescence in all or part of the range tested (5-40 degrees C). Specifically, the intensity of the single-wavelength dyes increased at low temperature. The ratiometric dyes, because of variable effects at the two wavelengths, showed, in general, a reduction in the fluorescence ratio as temperature decreased. Changes in viscosity, pH, oxygen quenching, or fluorescence maxima could not fully explain the effects of temperature on fluorescence. The excited-state lifetimes of the dyes were determined, in both the presence and absence of calcium, using multifrequency phase-modulation fluorimetry. In most cases, low temperature led to prolonged fluorescence lifetimes. The increase in lifetimes at reduced temperature is probably largely responsible for the effects of temperature on the physical properties of the calcium-sensing dyes. Clearly, these temperature effects can influence reported calcium concentrations and must therefore be taken into consideration during any investigation involving variable temperatures.
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Affiliation(s)
- A E Oliver
- Section of Molecular and Cellular Biology, University of California, Davis, Davis, CA 95616, USA.
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31
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Stowe DF, Fujita S, An J, Paulsen RA, Varadarajan SG, Smart SC. Modulation of myocardial function and [Ca2+] sensitivity by moderate hypothermia in guinea pig isolated hearts. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 277:H2321-32. [PMID: 10600852 DOI: 10.1152/ajpheart.1999.277.6.h2321] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cardiac hypothermia alters contractility and intracellular Ca2+ concentration ([Ca2+]i) homeostasis. We examined how left ventricular pressure (LVP) is altered as a function of cytosolic [Ca2+]i over a range of extracellular CaCl2 concentration ([CaCl2]e) during perfusion of isolated, paced guinea pig hearts at 37 degrees C, 27 degrees C, and 17 degrees C. Transmural LV phasic [Ca2+] was measured using the Ca2+ indicator indo 1 and calibrated (in nM) after correction was made for autofluorescence, temperature, and noncytosolic Ca2+. Noncytosolic [Ca2+]i, cytosolic diastolic and systolic [Ca2+]i, phasic [Ca2+]i, and systolic Ca2+ released per beat (area Ca2+) were plotted as a function of 0.3-4.5 mM [CaCl2]e, and indexes of contractility [LVP, maximal rates of LVP development (+dLVP/dt) and relaxation (-dLVP/dt), and the integral of the LVP curve per beat (LVParea)] were plotted as a function of [Ca2+]i. Hypothermia increased systolic [Ca2+]i and slightly changed systolic LVP but increased diastolic LVP and [Ca2+]i. The relationship of diastolic and noncytosolic [Ca2+] to [CaCl2]e was shifted upward at 17 degrees C and 27 degrees C, whereas that of phasic [Ca2+]) to [CaCl2]e was shifted upward at 17 degrees C but not at 27 degrees C. The relationships of phasic [Ca2+]i to developed LVP, +dLVP/dt, and LVP(area) were progressively reduced by hypothermia so that maximal Ca2+-activated LVP decreased and hearts were desensitized to Ca2+. Thus mild hypothermia modestly increases diastolic and noncytosolic Ca2+ with little effect on systolic Ca2+ or released (area) Ca2+, whereas moderate hypothermia markedly increases diastolic, noncytosolic, peak systolic, and released Ca2+ and results in reduced maximal Ca2+-activated LVP and myocardial sensitivity to systolic Ca2+.
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Affiliation(s)
- D F Stowe
- Department of Anesthesiology, Medical College of Wisconsin, Milwaukee 53226, USA.
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32
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Wang SQ, Zhou ZQ. Alpha-stat calibration of indo-1 fluorescence and measurement of intracellular free calcium in rat ventricular cells at different temperatures. Life Sci 1999; 65:871-7. [PMID: 10465347 DOI: 10.1016/s0024-3205(99)00317-3] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
To explore how to manage pH when calibrating Ca2+ probes at different temperatures, the dissociation constant (Kd) of indo-1 was determined both in pH-stat (pH is fixed despite the temperature) and in alpha-stat (pH changes with temperature as in cells). The results showed that the Kd was much more sensitive to temperature in pH-stat than in alpha-stat, demonstrating that alpha-stat calibration should be preferred when using a Ca2+ probe to measure intracellular free calcium ([Ca2+]i) at different temperatures. Based on the calibration in situ and in alpha-stat, we showed a striking increase of [Ca2+]i from 141+/-8 nM at 30 degrees C to 218+/-22 nM at 10 degrees C in indo-1 loaded rat ventricular cells, which supports that intracellular calcium overload takes place in cardiac myocytes of non-hibernating mammals during hypothermia.
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Affiliation(s)
- S Q Wang
- College of Life Sciences, Peking University, Beijing, China.
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33
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Wang S, Zhou Z, Qian H. Temperature dependence of intracellular free calcium in cardiac myocytes from rat and ground squirrel measured by confocal microscopy. ACTA ACUST UNITED AC 1999; 42:293-9. [DOI: 10.1007/bf03183606] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/1998] [Indexed: 10/19/2022]
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Chan EY, Stang SL, Bottorff DA, Stone JC. Hypothermic stress leads to activation of Ras-Erk signaling. J Clin Invest 1999; 103:1337-44. [PMID: 10225977 PMCID: PMC408355 DOI: 10.1172/jci5474] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
The small GTPase Ras is converted to the active, GTP-bound state during exposure of vertebrate cells to hypothermic stress. This activation occurs more rapidly than can be accounted for by spontaneous nucleotide exchange. Ras-guanyl nucleotide exchange factors and Ras GTPase-activating proteins have significant activity at 0 degrees C in vitro, leading to the hypothesis that normal Ras regulators influence the relative amounts of Ras-GTP and Ras-GDP at low temperatures in vivo. When hypothermic cells are warmed to 37 degrees C, the Raf-Mek-Erk protein kinase cascade is activated. After prolonged hypothermic stress, followed by warming to physiologic temperature, cultured fibroblasts assume a rounded morphology, detach from the substratum, and die. All of these biologic responses are attenuated by pharmacologic inhibition of Mek. Previously, it had been found that low temperature blocks acute growth factor signaling to Erk. In the present study, we found that this block occurs at the level of Raf activation. Temperature regulation of Ras signaling could help animal cells respond appropriately to hypothermic stress, and Ras-Erk signaling can be manipulated to improve the survival of cells in cold storage.
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Affiliation(s)
- E Y Chan
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada, T6G 2H7
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Murphy JT, Giroir B, Horton JW. Thermal injury alters myocardial sarcoplasmic reticulum calcium channel function. J Surg Res 1999; 82:244-52. [PMID: 10090836 DOI: 10.1006/jsre.1998.5537] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
BACKGROUND We have previously shown that a major cutaneous thermal injury produces profound cardiac contractile dysfunction despite adequate resuscitation. While the molecular basis of this dysfunction is unknown, recent work has suggested that alterations in calcium flux between the myocyte sarcoplasmic reticulum (SR) to the cytoplasm may play a role. MATERIALS AND METHODS To determine if thermal injury-induced contractile dysfunction is related to intracellular calcium transport across the SR membrane, we accessed myocardial microsomal preparations from scalded (43% TBSA) guinea pigs for the ability of the cardiac calcium efflux channel to bind radiolabeled ryanodine. Intracellular calcium flux was assessed by fluorescence spectrophotometry. RESULTS Thermal injury resulted in severe cardiac contractile deficit characterized by loss of LVP and +/-dP/dt despite resuscitation. Analysis of isolated myocyte cultures showed a twofold increase in cytoplasmic [Ca2+]l by 24 h postburn. Competitive binding and Scatchard analysis demonstrated a single, high-affinity binding site present in both sham and burn animal hearts. Myocardial membrane vesicles revealed a significantly enhanced number of calcium efflux channels in the open configuration at both 8 and 24 h following thermal injury compared to time-matched shams (1.07 +/- 0.01 and 0.95 +/- 0.06 vs 0.85 +/- 0.01 pmol bound/mg protein, P < 0.05). The data indicate that altered function of the myocardial transmembrane SR calcium efflux channel following thermal injury was associated with elevated [Ca2+]l and contractile dysfunction. CONCLUSIONS We conclude that postburn cardiac dysfunction may partly be a result of elevated cytoplasmic calcium concentrations and diminished regulation of SR calcium efflux channel activity.
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Affiliation(s)
- J T Murphy
- Department of Surgery, University of Texas Southwestern Medical Center, Dallas, Texas, 75235, USA
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36
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Lathrop DA, Contney SJ, Bosnjak ZJ, Stowe DF. Reversal of hypothermia-induced action potential lengthening by the KATP channel agonist bimakalim in isolated guinea pig ventricular muscle. GENERAL PHARMACOLOGY 1998; 31:125-31. [PMID: 9595290 DOI: 10.1016/s0306-3623(97)00395-9] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
1. ATP-sensitive potassium (KATP) channel openers shorten cardiac ventricular muscle action potential duration (APD), reduce resting and developed contractile force, and have been shown to provide cardioprotection when given before, during, and after either short-term ischemia or long-term hypothermia. The authors' aim was to determine the concentration-dependent effect of the potent KATP channel opener bimakalim on transmembrane action potential changes induced by mild (27 degrees C) and moderate (20 degrees C) hypothermia in isolated guinea pig ventricular muscle. 2. Conventional microelectrode techniques were used to record action potentials (APs) in single myocytes during normothermia (37 degrees C) and hypothermia in the presence and absence of 0.1 to 30 mumol.l-1 bimakalim. 3. Hypothermia alone increased APD and depolarized the diastolic membrane potential (DMP): APD90 = 141.7 +/- 7.0 msec and DMP -86.2 +/- 1.4 mV (n = 6) at 37 degrees C versus 235.7 +/- 7.8 msec and -75.6 +/- 1.0 mV at 20 degrees C (n = 7). At 37 degrees C, bimakalim (0.1-10 mumol.l-1) shortened APD in a concentration-dependent fashion. 4. APD90 was markedly reduced from 141.7 +/- 7.0 msec without bimakalim to 9.5 +/- 2.6 msec with 10 mumol.l-1 bimakalim (n = 6); this effect was blocked by glibenclamide. DMP was hyperpolarized by bimakalim. More bimakalim was required to shorten APs during mild and moderate hypothermia. The 50% effective concentration (EC50) of bimakalim required to maximally shorten APD90 was 0.96 +/- 0.10 mumol.l-1 at 37 degrees C; this increased to 3.96 +/- 0.24 mumol.l-1 at 27 degrees C, and to 12.34 +/- 0.72 mumol.l-1 at 20 degrees C. Relative to hypothermia-induced depolarization, bimakalim hyperpolarized DMP toward drug-free values obtained at 37 degrees C. 5. These results indicate that hypothermia shifts the bimakalim concentration APD90 response curve to the right such that 13 times more bimakalim is required at 20 degrees C shorten APD by the same amount as at 37 degrees C. Bimakalim also reverses hypothermia-induced AP lengthening and tends to reverse the hypothermia-induced decrease in DMP. 6. These findings aid in our understanding of the cardioprotective effects of KATP channel openers during hypothermia.
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Affiliation(s)
- D A Lathrop
- Department of Anesthesiology, Medical College of Wisconsin, Milwaukee 53226, USA
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37
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Wang SQ, Huang YH, Liu KS, Zhou ZQ. Dependence of myocardial hypothermia tolerance on sources of activator calcium. Cryobiology 1997; 35:193-200. [PMID: 9367607 DOI: 10.1006/cryo.1997.2040] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
To determine the relationship between cardiac hypothermia tolerance and the sources of activator calcium, we selectively modified either the sarcolemmal calcium permeability by nifedipine or the sarcoplasmic reticulum function by caffeine in papillary muscles from both the rat, as a cold sensitive model, and the ground squirrel, Citellus dauricus, a deep hibernator. Both force-interval relationship and cooling performance were investigated. At 25 degrees C, the slope of the force-interval curve of the ground squirrel was nearly double that of the rat. At shorter test intervals 0.5 muM nifedipine moved the curve down with little effect at longer intervals, and the curve slope increased. Caffeine (1 mM) decreased the peak force and eliminated its dependence upon test interval. When the temperature was lowered, rat preparations showed a marked increase of resting tension and aftercontraction between 7 and 12 degrees C and became inexcitable. In contrast, they maintained contractility down to a few degrees above 0 degrees C without aftercontraction and increased resting tension in the ground squirrel. In the rat nifedipine shortened the contractions, prevented the increase of resting tension, and minimized aftercontractions, with little improvement of contractility. Caffeine prolonged the contractions, caused a striking increase of resting tension and aftercontractions, and finally disabled the contractility at about 5-10 degrees C, even in the ground squirrel. We conclude that depressed calcium influx helps to prevent hypothermic calcium overload of the cardiac cells. Good function of the sarcoplasmic reticulum is essential for tolerance of hypothermia by cardiac cells. A suggestion that may improve the hypothermic tolerance of the myocardium from nonhibernators is postulated.
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Affiliation(s)
- S Q Wang
- College of Life Sciences, Peking University, Beijing, 100871, People's Republic of China
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38
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Lahorra JA, Torchiana DF, Tolis G, Bashour CA, Hahn C, Titus JS, Geffin GA, Daggett WM. Rapid cooling contracture with cold cardioplegia. Ann Thorac Surg 1997; 63:1353-60. [PMID: 9146327 DOI: 10.1016/s0003-4975(97)00087-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
BACKGROUND Cold cardioplegia can induce rapid cooling contracture. The relations of cardioplegia-induced cooling contracture to myocardial temperature or myocyte calcium are unknown. METHODS Twelve crystalloid-perfused isovolumic rat hearts received three 2-minute cardioplegic infusions (1 mmol/L calcium) at 4 degrees, 20 degrees, and 37 degrees C in random order, each followed by 10 minutes of beating at 37 degrees C. Finally, warm induction of arrest by a 1-minute cardioplegic infusion at 37 degrees C was followed by a 1-minute infusion at 4 degrees C. Indo-1 was used to measure the intracellular Ca2+ concentration in 6 of these hearts. Additional hearts received hypoxic, glucose-free cardioplegia at 4 degrees or 37 degrees C. RESULTS After 1 minute of cardioplegia at 4 degrees, 20 degrees, and 37 degrees C, left ventricular developed pressure rose rapidly to 54% +/- 3%, 43% +/- 3%, and 18% +/- 1% of its prearrest value, whereas the intracellular Ca2+ concentration reached 166% +/- 23%, 94% +/- 4%, and 37% +/- 10% of its prearrest transient. Coronary flow was 5.7 +/- 0.2, 8.7 +/- 0.3, and 12.6 +/- 0.6 mL/min, respectively. Warm cardioplegia induction at 37 degrees C reduced left ventricular developed pressure and [Ca2+]i during subsequent 4 degrees C cardioplegia by 16% (p = 0.001) and 34% (p = 0.03), respectively. Adenosine triphosphate and phosphocreatine contents were lower after 4 degrees C than after 37 degrees C hypoxic, glucose-free cardioplegia. CONCLUSIONS Rapid cooling during cardioplegia increases left ventricular pressure, [Ca2+]i and coronary resistance, and is energy consuming. The absence of rapid cooling contracture may be a benefit of warm heart operations and warm induction of cardioplegic arrest.
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Affiliation(s)
- J A Lahorra
- Cardiac Surgical Unit, Massachusetts General Hospital, Harvard Medical School, Boston, USA
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39
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Belke DD, Wang LC, Lopaschuk GD. Effects of hypothermia on energy metabolism in rat and Richardson's ground squirrel hearts. J Appl Physiol (1985) 1997; 82:1210-8. [PMID: 9104858 DOI: 10.1152/jappl.1997.82.4.1210] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Glycolysis, glucose oxidation, palmitate oxidation, and cardiac function were measured in isolated working hearts from ground squirrels and rats subjected to a hypothermia-rewarming protocol. Hearts were perfused initially for 30 min at 37 degrees C, followed by 2 h of hypothermic perfusion at 15 degrees C, after which hearts were rewarmed to 37 degrees C and further perfused for 30 min. Functional recovery in ground squirrel hearts was greater than in rat hearts after rewarming. Hypothermia-rewarming had a similar general effect on the various metabolic pathways in both species. Despite these similarities, total energy substrate metabolic rates were greater in rat than ground squirrel hearts during hypothermia despite a lower level of work being performed by the rat hearts, indicating that rat hearts are less efficient than ground squirrel hearts during hypothermia. After rewarming, energy substrate metabolism recovered completely in both species, although cardiac work remained depressed in rat hearts. The difference in functional recovery between rat and ground squirrel hearts after rewarming cannot be explained by general differences in energy substrate metabolism during hypothermia or after rewarming.
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Affiliation(s)
- D D Belke
- Department of Pharmacology, University of Alberta, Edmonton, Canada
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40
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Morii I, Kihara Y, Konishi T, Inubushi T, Sasayama S. Mechanism of the negative force-frequency relationship in physiologically intact rat ventricular myocardium--studies by intracellular Ca2+ monitor with indo-1 and by 31P-nuclear magnetic resonance spectroscopy. JAPANESE CIRCULATION JOURNAL 1996; 60:593-603. [PMID: 8889662 DOI: 10.1253/jcj.60.593] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
We studied the subcellular mechanisms of the negative force-frequency relationship in rat myocardium by measuring 1) intracellular Ca2+ transients by indo-1 fluorometry and 2) intracellular pH (pHi) and phosphate compounds with 31P-nuclear magnetic resonance (NMR). The data were compared with those from guinea pig hearts, which show a positive force-frequency relationship. By increasing the pacing rate from 3 Hz to 5 Hz, the peak positive first derivative of left ventricular pressure (LVdP/dt) in rat heart decreased by 10 +/- 1% (n = 6). In contrast to this negative inotropic response, simultaneously measured peak Ca2+ transients increased by 6 +/- 1%. Guinea pig heart (n = 6) showed an increase in peak positive LVdP/dt (33 +/- 1%) which was associated with an increase in peak Ca2+ transients (8 +/- 1%). Under equivalent experimental conditions in an NMR spectrometer, this increase in the pacing rate did not affect intracellular levels of phosphate compounds in either rat (n = 6) or guinea pig heart (n = 6). In contrast, pHi showed a decrease of 0.031 +/- 0.006 pH units in rat heart, while no changes were observed in guinea pig heart. These results suggest that in physiological rat myocardium, pHi is susceptible to changes in the stimulus frequency and may affect the Ca(2+)-responsiveness of contractile proteins, which results in the negative force-frequency relationship.
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Affiliation(s)
- I Morii
- Department of Internal Medicine, Kyoto University Faculty of Medicine, Japan
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41
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Alekseev AE, Markevich NI, Korystova AF, Terzic A, Kokoz YM. Comparative analysis of the kinetic characteristics of L-type calcium channels in cardiac cells of hibernators. Biophys J 1996; 70:786-97. [PMID: 8789095 PMCID: PMC1224978 DOI: 10.1016/s0006-3495(96)79618-2] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
An undefined property of L-type Ca2+ channels is believed to underlie the unique phenotype of hibernating hearts. Therefore, L-type Ca2+ channels in single cardiomyocytes isolated from hibernating versus awake ground-squirrels (Citellus undulatus) were compared using the perforated mode of the patch-clamp technique, and interpreted by way of a kinetic model of Ca2+ channel behavior based upon the concept of independence of the activation and inactivation processes. We find that, in hibernating ground-squirrels, the cardiac L-type Ca2+ current is lower in magnitude when compared to awake animals. Both in the awake or hibernating states, kinetics of L-type Ca2+ channels could be described by a d2f1(2)f2 model with an activation and two inactivation processes. The activation (or d) process relates to the movement of the gating charge. The slow (or f1) inactivation is associated with movement of gating charge and is current-dependent. The rapid (or f2) inactivation is a complex process which cannot be represented as a single-step conformational transition induced by the gating charge movement, and is regulated by beta-adrenoceptor stimulation. When compared to awake animals, the kinetic properties of Ca2+ channels from hibernating ground-squirrels differed in the following parameters: (1) pronounced shift (15-20 mV) toward depolarization in the normalized conductance of both inactivation components, and moderate shift in the activation component; (2) 1.5-2-fold greater time constants; and (3) two-fold greater activation gating charge. Thus, L-type Ca2+ channels apparently switch their phenotype during the hibernating transition. Stimulation of beta-adrenoceptors by isoproterenol, reversed the hibernating kinetic- (but not amplitude-) phenotype toward the awake type. Therefore, an aberrance in the beta-adrenergic system can not fully explain the observed changes in the L-type Ca2+ current. This suggests that during hibernation additional mechanisms may reduce the single Ca2+ channel-conductance and/or keep a fraction of the cardiac L-type Ca2+ channel population in a non-active state.
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Affiliation(s)
- A E Alekseev
- Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, Pushchino, Russia.
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Tsutsui H, Urabe Y, Mann DL, Tagawa H, Carabello BA, Cooper G, Zile MR. Effects of chronic mitral regurgitation on diastolic function in isolated cardiocytes. Circ Res 1993; 72:1110-23. [PMID: 8477523 DOI: 10.1161/01.res.72.5.1110] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
We have previously shown that chronic mitral regurgitation (MR) increases the rate of left ventricular early diastolic filling. These changes in chamber diastolic function were felt to be secondary to alterations in left ventricular loading conditions. Therefore, cellular diastolic function measured in cardiac muscle cells (cardiocytes) isolated from animals with chronic MR (absent alterations in loading conditions) was expected to be normal. However, chronic MR caused a decrease in sarcomere lengthening rate. The purpose of the current study was to define the mechanisms causing this decreased sarcomere lengthening rate in chronic MR cardiocytes and to explain the apparent dichotomy between chamber and cellular diastolic properties. Accordingly, sarcomere motion was measured using laser diffraction techniques in enzymatically isolated cardiocytes from seven control dogs and 11 dogs with chronic MR (produced by closed-chest transection of the mitral chordae). In the MR cardiocytes, there were abnormalities in cellular systolic function (decreased extent and velocity of shortening) and in cellular diastolic function (decreased velocity of sarcomere lengthening). Because studies in papillary muscles have shown that there is a direct relation between abnormal diastolic function (decreased velocity of muscle lengthening) and abnormal systolic function (decreased extent of muscle shortening), it was unclear whether the changes in cellular relaxation rate observed in chronic MR merely reflected a concomitant decrease in the extent of shortening or instead reflected an impairment in intrinsic relaxation properties. To make this distinction, the relation between relaxation velocity (measured as peak sarcomere lengthening rate) and sarcomere shortening extent was examined in MR cardiocytes and compared with that in control cardiocytes. There was a direct relation between sarcomere relaxation velocity and sarcomere shortening extent in both control and MR cardiocytes. Over a wide range of shortening extent, the slopes and y intercepts of this relation were similar in control and MR cardiocytes (slope, 27.7 sec-1 in control cells versus 28.1 sec-1 in MR cells; y intercept, -1.1 microns/sec in control cells versus -1.7 microns/sec in MR cells; p = NS). At any common shortening extent, relaxation velocity was the same in control and MR cardiocytes. To prove that this relation could detect abnormalities in the intrinsic myocardial relaxation process, interventions known to produce primary alterations in the intrinsic myocardial relaxation process were examined: the effects of hypothermia (30 degrees C) and isoproterenol (10(-6) M) on the relaxation velocity-shortening extent relation were studied in normal and MR cardiocytes.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- H Tsutsui
- Gazes Cardiac Research Institute, Cardiology Division of the Department of Medicine, Medical University of South Carolina, Charleston 29425-5799
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Figueredo VM, Brandes R, Weiner MW, Massie BM, Camacho SA. Endocardial versus epicardial differences of intracellular free calcium under normal and ischemic conditions in perfused rat hearts. Circ Res 1993; 72:1082-90. [PMID: 8477520 DOI: 10.1161/01.res.72.5.1082] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Transmural heterogeneity of myocardial metabolism and function are present in the left ventricle under normal and ischemic conditions. To determine if endocardial versus epicardial differences of [Ca2+]i are also present, perfused rat heart studies using indo-1 fluorescence as an index of [Ca2+]i were performed in the left ventricular epicardium and endocardium. Hearts were studied during control conditions and low-flow ischemia. Results demonstrated the following: 1) At a pacing rate of 1.5 Hz, endocardial levels of diastolic and systolic [Ca2+]i (470 +/- 40 and 1,240 +/- 170 nM) were higher than epicardial levels (290 +/- 30 and 920 +/- 150 nM). 2) At a more physiological pacing rate of 5 Hz, endocardial levels of diastolic and systolic [Ca2+]i (680 +/- 50 and 1,230 +/- 70 nM) were also higher than epicardial levels (390 +/- 20 and 950 +/- 60 nM. 3) During low-flow ischemia, endocardial levels of diastolic [Ca2+]i rose to a greater degree (from 680 +/- 50 to 1,050 +/- 70 nM at 10% of control coronary flow) compared with epicardial levels (from 390 +/- 20 to 580 +/- 40 nM at 10% of control flow), suggesting that the endocardium is more susceptible to low-flow ischemia. 4) The amplitude of the [Ca2+]i transient was the same at the endocardium (540 +/- 50 nM) and epicardium (560 +/- 50 nM) and did not change during low-flow ischemia, despite marked contractile dysfunction.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- V M Figueredo
- Department of Medicine (Cardiology), University of California, San Francisco
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Dynlacht JR, Hyun WC, Dewey WC. Changes in intracellular free calcium during hyperthermia: effects of local anesthetics and induction of thermotolerance. CYTOMETRY 1993; 14:223-9. [PMID: 8440156 DOI: 10.1002/cyto.990140216] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We wished to determine if local anesthetics (LAs) induced changes in intracellular free calcium ([fCa2+i]) that could have an effect on cell killing by hyperthermia. Flow cytometry was used to measure [fCa2+i] of mouse NIH 3T3 cells during heating at 45.5 degrees C. In both non-tolerant and thermotolerant cells, heating caused a rapid increase (within 1 min) in [fCa2+i] of approximately 100 nM, which remained relatively constant during 25 min of continued heating; however, survival was higher in thermotolerant cells. Procaine, lidocaine, and tetracaine had no effect on survival or [fCa2+i] of cells kept at 37 degrees C up to 25 min. Cells heated with procaine and lidocaine showed no difference in [fCa2+i] compared to cells heated without LAs but were greatly sensitized to killing. Cells heated with tetracaine became permeable to trypan blue within 10-15 min of heating. We conclude that heat sensitization by LAs does not involve changes in [fCa2+i]. Furthermore, these studies reject the hypothesis that changes in [fCa2+i] are involved in heat-induced cell killing.
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Affiliation(s)
- J R Dynlacht
- Department of Radiation Oncology, University of California, San Francisco 94143-0806
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Fedida D, Bouchard RA. Mechanisms for the positive inotropic effect of alpha 1-adrenoceptor stimulation in rat cardiac myocytes. Circ Res 1992; 71:673-88. [PMID: 1323437 DOI: 10.1161/01.res.71.3.673] [Citation(s) in RCA: 60] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
alpha 1-Adrenoceptor activation can enhance myocardial contractility, and two possible inotropic mechanisms are an increase in myofilament Ca2+ sensitivity and action potential prolongation, which can increase net Ca2+ entry into cells. In adult rat ventricular myocytes (bath Ca2+, 1 mM; stimulated at 0.2-0.5 Hz), the drug 4-aminopyridine and the whole-cell voltage clamp have been used to control Ca2+ entry and differentiate between the two mechanisms. At 22-23 degrees C the specific alpha 1-adrenoceptor agonist methoxamine (100 microM) prolonged action potential duration at 50% repolarization from 55 +/- 2 to 81 +/- 5 msec, delayed time to peak contraction, and increased shortening amplitude from 5.3 +/- 0.6 to 7.8 +/- 1 microns (n = 18). Reduction of the transient outward current and other K+ currents by methoxamine was the major cause of action potential prolongation in rat myocytes with little change in the L-type calcium current. Block of the transient outward current with 2 mM 4-aminopyridine prolonged action potential duration from 52 +/- 6 to 98 +/- 12 msec and increased unloaded cell shortening from 2.9 +/- 0.4 to 6.6 +/- 0.6 microns (n = 4). Subsequently, methoxamine no longer increased cell shortening, although significant potentiation of twitch amplitude was still seen after a brief rest interval. In voltage-clamp experiments, with 70-500-msec pulses, although membrane currents were reduced, methoxamine had no positive inotropic effect and reduced cell shortening from 5.3 +/- 0.7 to 4.97 +/- 0.8 microns at pulse potentials positive to -40 mV. Similar alpha 1-adrenoceptor responses were observed at 35 degrees C during action potential and voltage-clamp experiments, which could be blocked by 10 microM prazosin. In myocytes loaded with the Ca2+ indicator indo-1, alpha 1-adrenoceptor stimulation or 4-aminopyridine both increased cell contraction and intracellular Ca2+ transients by similar amounts. As in unloaded cells, prior exposure to 4-aminopyridine prevented any inotropic effect of methoxamine without changing the systolic intracellular Ca2+ transient. The results indicated that under our experimental conditions positive inotropy in rat cardiomyocytes on exposure to alpha 1-adrenoceptor agonists was strongly correlated with the action potential prolongation that accompanied K+ current reduction. In addition, modulation of K+ channels could occur independent of changes in contractility and/or [Ca2+]i.
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Affiliation(s)
- D Fedida
- Department of Physiology, Queen's University, Kingston, Canada
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Vostal J, Jackson W, Shulman N. Cytosolic and stored calcium antagonistically control tyrosine phosphorylation of specific platelet proteins. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)55389-8] [Citation(s) in RCA: 87] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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