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Abramochkin DV, Filatova TS, Pustovit KB, Voronina YA, Kuzmin VS, Vornanen M. Ionic currents underlying different patterns of electrical activity in working cardiac myocytes of mammals and non-mammalian vertebrates. Comp Biochem Physiol A Mol Integr Physiol 2022; 268:111204. [PMID: 35346823 DOI: 10.1016/j.cbpa.2022.111204] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2022] [Revised: 03/21/2022] [Accepted: 03/22/2022] [Indexed: 12/19/2022]
Abstract
The orderly contraction of the vertebrate heart is determined by generation and propagation of cardiac action potentials (APs). APs are generated by the integrated activity of time- and voltage-dependent ionic channels which carry inward Na+ and Ca2+ currents, and outward K+ currents. This review compares atrial and ventricular APs and underlying ion currents between different taxa of vertebrates. We have collected literature data and attempted to find common electrophysiological features for two or more vertebrate groups, show differences between taxa and cardiac chambers, and indicate gaps in the existing data. Although electrical excitability of the heart in all vertebrates is based on the same superfamily of channels, there is a vast variability of AP waveforms between atrial and ventricular myocytes, between different species of the same vertebrate class and between endothermic and ectothermic animals. The wide variability of AP shapes is related to species-specific differences in animal size, heart rate, stage of ontogenetic development, excitation-contraction coupling, temperature and oxygen availability. Some of the differences between taxa are related to evolutionary development of genomes, which appear e.g. in the expression of different Na+ and K+ channel orthologues in cardiomyocytes of vertebrates. There is a wonderful variability of AP shapes and underlying ion currents with which electrical excitability of vertebrate heart can be generated depending on the intrinsic and extrinsic conditions of animal body. This multitude of ionic mechanisms provides excellent material for studying how the function of the vertebrate heart can adapt or acclimate to prevailing physiological and environmental conditions.
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Affiliation(s)
- Denis V Abramochkin
- Department of Human and Animal Physiology, Lomonosov Moscow State University, Leninskiye gory, 1, 12, Moscow 119234, Russia.
| | - Tatiana S Filatova
- Department of Human and Animal Physiology, Lomonosov Moscow State University, Leninskiye gory, 1, 12, Moscow 119234, Russia
| | - Ksenia B Pustovit
- Department of Human and Animal Physiology, Lomonosov Moscow State University, Leninskiye gory, 1, 12, Moscow 119234, Russia
| | - Yana A Voronina
- Department of Human and Animal Physiology, Lomonosov Moscow State University, Leninskiye gory, 1, 12, Moscow 119234, Russia; Laboratory of Cardiac Electrophysiology, National Medical Research Center for Cardiology, 3(rd) Cherepkovskaya str., 15A, Moscow, Russia
| | - Vladislav S Kuzmin
- Department of Human and Animal Physiology, Lomonosov Moscow State University, Leninskiye gory, 1, 12, Moscow 119234, Russia; Department of Physiology, Pirogov Russian National Research Medical University, Ostrovityanova str., 1, Moscow, Russia
| | - Matti Vornanen
- Department of Environmental and Biological Sciences, University of Eastern Finland, Joensuu, Finland
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Sparks K, Couturier CS, Buskirk J, Flores A, Hoeferle A, Hoffman J, Stecyk JAW. Gene expression of hypoxia-inducible factor (HIF), HIF regulators, and putative HIF targets in ventricle and telencephalon of Trachemys scripta acclimated to 21 °C or 5 °C and exposed to normoxia, anoxia or reoxygenation. Comp Biochem Physiol A Mol Integr Physiol 2022; 267:111167. [PMID: 35182763 PMCID: PMC8977064 DOI: 10.1016/j.cbpa.2022.111167] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2022] [Revised: 02/10/2022] [Accepted: 02/10/2022] [Indexed: 12/20/2022]
Abstract
In anoxia-sensitive mammals, hypoxia inducible factor (HIF) promotes cellular survival in hypoxia, but also tumorigenesis. By comparison, anoxia-tolerant vertebrates likely need to circumvent a prolonged upregulation of HIF to survive long-term anoxia, making them attractive biomedical models for investigating HIF regulation. To lend insight into the role of HIF in anoxic Trachemys scripta ventricle and telencephalon, 21 °C- and 5 °C-acclimated turtles were exposed to normoxia, anoxia (24 h at 21 °C; 24 h or 14 d at 5 °C) or anoxia + reoxygenation and the gene expression of HIF-1α (hif1a) and HIF-2α (hif2a), two regulators of HIF, and eleven putative downstream targets of HIF quantified by qPCR. Changes in gene expression with anoxia at 21 °C differentially aligned with a circumvention of HIF activity. Whereas hif1a and hif2a expression was unaffected in ventricle and telencephalon, and BCL2 interacting protein 3 gene expression reduced by 30% in telencephalon, gene expression of vascular endothelial growth factor-A increased in ventricle (4.5-fold) and telencephalon (1.5-fold), and hexokinase 1 (2-fold) and hexokinase 2 (3-fold) gene expression increased in ventricle. At 5 °C, the pattern of gene expression in ventricle or telencephalon was unaltered with oxygenation state. However, cold acclimation in normoxia induced downregulation of HIF-1α, HIF-2α, and HIF target gene expression in telencephalon. Overall, the findings lend support to the postulation that prolonged activation of HIF is counterproductive for long-term anoxia survival. Nevertheless, quantification of the effect of anoxia and acclimation temperature on HIF binding activity and regulation at the protein level are needed to provide a strong scientific framework whereby new strategies for oxygen related pathologies can be developed.
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Affiliation(s)
- Kenneth Sparks
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, United States
| | - Christine S Couturier
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, United States
| | - Jacob Buskirk
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, United States
| | - Alicia Flores
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, United States
| | - Aurora Hoeferle
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, United States
| | - Jessica Hoffman
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, United States
| | - Jonathan A W Stecyk
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, United States.
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Garner M, Barber RG, Cussins J, Hall D, Reisinger J, Stecyk JA. Does the ventricle limit cardiac contraction rate in the anoxic turtle (Trachemys scripta)? II. In vivo and in vitro assessment of the prevalence of cardiac arrhythmia and atrioventricular block. Curr Res Physiol 2022; 5:292-301. [PMID: 35856059 PMCID: PMC9287599 DOI: 10.1016/j.crphys.2022.07.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Revised: 06/27/2022] [Accepted: 07/04/2022] [Indexed: 11/15/2022] Open
Abstract
Previous studies have reported evidence of atrio-ventricular (AV) block in the oxygen-limited Trachemys scripta heart. However, if cardiac arrhythmia occurs in live turtles during prolonged anoxia exposure remains unknown. Here, we compare the effects of prolonged anoxic submergence and subsequent reoxygenation on cardiac electrical activity through in vivo electrocardiogram (ECG) recordings of 21 °C- and 5 °C-acclimated turtles to assess the prevalence of cardiac arrhythmia. Additionally, to elucidate the influence of extracellular conditions on the prominence of cardiac arrhythmia, we exposed spontaneously contracting T. scripta right atrium and electrically coupled ventricle strip preparations to extracellular conditions that sequentially and additively approximated the shift from the normoxic to anoxic extracellular condition of warm- and cold-acclimated turtles. Cardiac arrhythmia was prominent in 21 °C anoxic turtles. Arrhythmia was qualitatively evidenced by groupings of contractions in pairs and trios and quantified by an increased coefficient of variation of the RR interval. Similarly, exposure to combined anoxia, acidosis, and hyperkalemia induced arrhythmia in vitro that was not counteracted by hypercalcemia or combined hypercalcemia and heightened adrenergic stimulation. By comparison, cold acclimation primed the turtle heart to be resilient to cardiac arrhythmia. Although cardiac irregularities were present intermittently, no change in the variation of the RR interval occurred in vivo with prolonged anoxia exposure at 5 °C. Moreover, the in vitro studies at 5 °C highlighted the importance of adrenergic stimulation in counteracting AV block. Finally, at both acclimation temperatures, cardiac arrhythmia and irregularities ceased upon reoxygenation, indicating that the T. scripta heart recovers from anoxia-induced disruptions to cardiac excitation. Cardiac arrhythmia was prominent in 21 °C anoxic turtles. Cold acclimation primes the turtle heart to be resilient to the cardiac arrhythmia induced by prolonged anoxic submergence. Adrenergic stimulation counteracts atrioventricular block at 5 °C. The turtle heart recovers from anoxia-induced disruptions to cardiac electrical activity.
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Affiliation(s)
| | | | | | | | | | - Jonathan A.W. Stecyk
- Corresponding author. Stecyk Department of Biological Sciences, University of Alaska Anchorage, 3211 Providence Drive, Anchorage, AK, 99508, USA.
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Shiels HA, White E, Couturier CS, Hall D, Royal S, Galli GL, Stecyk JA. The air-breathing Alaska blackfish (Dallia pectoralis) remodels ventricular Ca2+ cycling with chronic hypoxic submergence to maintain ventricular contractility. Curr Res Physiol 2022; 5:25-35. [PMID: 35072107 PMCID: PMC8763628 DOI: 10.1016/j.crphys.2022.01.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Revised: 12/22/2021] [Accepted: 01/06/2022] [Indexed: 11/24/2022] Open
Abstract
The Alaska blackfish (Dallia pectoralis) is a facultative air-breather endemic to northern latitudes where it remains active in winter under ice cover in cold hypoxic waters. To understand the changes in cellular Ca2+ cycling that allow the heart to function in cold hypoxic water, we acclimated Alaska blackfish to cold (5 °C) normoxia or cold hypoxia (2.1–4.2 kPa; no air access) for 5–8 weeks. We then assessed the impact of the acclimation conditions on intracellular Ca2+ transients (Δ[Ca2+]i) of isolated ventricular myocytes and contractile performance of isometrically-contracting ventricular strips. Measurements were obtained at various contractile frequencies (0.2–0.6 Hz) in normoxia, during acute exposure to hypoxia, and reoxygenation at 5 °C. The results show that hypoxia-acclimated Alaska blackfish compensate against the depressive effects of hypoxia on excitation-contraction coupling by remodelling cellular Δ[Ca2+]i to maintain ventricular contractility. When measured at 0.2 Hz in normoxia, hypoxia-acclimated ventricular myocytes had a 3.8-fold larger Δ[Ca2+]i peak amplitude with a 4.1-fold faster rate of rise, compared to normoxia-acclimated ventricular myocytes. At the tissue level, maximal developed force was 2.1-fold greater in preparations from hypoxia-acclimated animals. However, maximal attainable contraction frequencies in hypoxia were lower in hypoxia-acclimated myocytes and strips than preparations from normoxic animals. Moreover, the inability of hypoxia-acclimated ventricular myocytes and strips to contract at high frequency persisted upon reoxygenation. Overall, the findings indicate that hypoxia alters aspects of Alaska blackfish cardiac myocyte Ca2+ cycling, and that there may be consequences for heart rate elevation during hypoxia, which may impact cardiac output in vivo. The air-breathing Alaska blackfish remains active under ice cover in hypoxic waters. Maintained activity is supported by compensation of intracellular Ca2+ transients. The compensation permits greater ventricular maximal developed force. However, maximal attainable contraction frequencies are limited by hypoxia exposure.
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Garner M, Stecyk JA. Does the ventricle limit cardiac contraction rate in the anoxic turtle (Trachemys scripta)? I. Comparison of the intrinsic contractile responses of cardiac chambers to the extracellular changes that accompany prolonged anoxia exposure. Curr Res Physiol 2022; 5:312-326. [PMID: 35872835 PMCID: PMC9301509 DOI: 10.1016/j.crphys.2022.07.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Revised: 05/27/2022] [Accepted: 07/04/2022] [Indexed: 11/24/2022] Open
Abstract
Multiple lines of evidence suggest that an inability of the ventricle to contract in coordination with the pacemaker during anoxia exposure may suppress cardiac pumping rate in anoxia-tolerant turtles. To determine under what extracellular conditions the ventricle could be the weak link that limits cardiac pumping, we compared, under various extracellular conditions, the intrinsic contractile properties of isometrically-contracting ventricular and atrial strips obtained from 21 °C- to 5 °C- acclimated turtles (Trachemys scripta) that had been exposed to either normoxia or anoxia (16 h at 21 °C; 12 days at 5 °C). We found that combined extracellular anoxia, acidosis, and hyperkalemia (AAK), severely disrupted ventricular, but not right or left atrial, excitability and contractibility of 5 °C anoxic turtles. However, combined hypercalcemia and heightened adrenergic stimulation counteracted the negative effects of AAK. We also report that the turtle heart is resilient to prolonged diastolic intervals, which would ensure that contractile force is maintained if arrhythmia were to occur during anoxia exposure. Finally, our findings reinforce that prior temperature and anoxia experiences are central to the intrinsic contractile response of the turtle myocardium to altered extracellular conditions. At 21 °C, prior anoxia exposure preconditioned the ventricle for anoxic and acidosis exposure. At 5 °C, prior anoxia exposure evoked heightened sensitivity of the ventricle to hyperkalemia, as well as all chambers to combined hypercalcemia and increased adrenergic stimulation. Overall, our findings show that the ventricle could limit cardiac pumping rate during prolonged anoxic submergence in cold-acclimated turtles if hypercalcemia and heightened adrenergic stimulation are insufficient to counteract the negative effects of combined extracellular anoxia, acidosis, and hyperkalemia. Turtle atria are more resilient to extracellular factors that disrupt contraction than the ventricle. Combined anoxia, acidosis, and hyperkalemia disrupted ventricular excitability and contractibility of 5 °C anoxic turtles. Heightened adrenergic stimulation counteracted the negative effects. The ventricle could limit cardiac pumping during anoxia at 5 °C if adrenergic stimulation is low.
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