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Ekström A, Hendriks B, Van Wert JC, Gilbert MJH, Farrell AP, Cooke SJ, Patterson DA, Hinch SG, Eliason EJ. Impairing cardiac oxygen supply in swimming coho salmon compromises their heart function and tolerance to acute warming. Sci Rep 2023; 13:21204. [PMID: 38040741 PMCID: PMC10692232 DOI: 10.1038/s41598-023-47713-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2023] [Accepted: 11/17/2023] [Indexed: 12/03/2023] Open
Abstract
Climatic warming elevates mortality for many salmonid populations during their physically challenging up-river spawning migrations, yet, the mechanisms underlying the increased mortality remain elusive. One hypothesis posits that a cardiac oxygen insufficiency impairs the heart's capacity to pump sufficient oxygen to body tissues to sustain up-river swimming, especially in warm water when oxygen availability declines and cardiac and whole-animal oxygen demand increases. We tested this hypothesis by measuring cardiac and metabolic (cardiorespiratory) performance, and assessing the upper thermal tolerance of coho salmon (Oncorhynchus kisutch) during sustained swimming and acute warming. By surgically ligating the coronary artery, which naturally accumulates arteriosclerotic lesions in migrating salmon, we partially impaired oxygen supply to the heart. Coronary ligation caused drastic cardiac impairment during swimming, even at benign temperatures, and substantially constrained cardiorespiratory performance during swimming and progressive warming compared to sham-operated control fish. Furthermore, upper thermal tolerance during swimming was markedly reduced (by 4.4 °C) following ligation. While the cardiorespiratory capacity of female salmon was generally lower at higher temperatures compared to males, upper thermal tolerance during swimming was similar between sexes within treatment groups. Cardiac oxygen supply is a crucial determinant for the migratory capacity of salmon facing climatic environmental warming.
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Affiliation(s)
- Andreas Ekström
- Department of Biological and Environmental Sciences, University of Gothenburg, PO Box 463, 40530, Gothenburg, Sweden.
| | - Brian Hendriks
- Pacific Salmon Ecology and Conservation Laboratory, Department of Forest and Conservation Sciences, The University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
| | - Jacey C Van Wert
- Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA, 93106-9620, USA
| | - Matthew J H Gilbert
- Department of Zoology, The University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
| | - Anthony P Farrell
- Department of Zoology, The University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
| | - Steven J Cooke
- Fish Ecology and Conservation Physiology Laboratory, Department of Biology, Carleton University, Ottawa, ON, K1S 5B6, Canada
| | - David A Patterson
- Fisheries and Oceans Canada, Cooperative Resource Management Institute, School of Resource and Environmental Management, Simon Fraser University, Burnaby, BC, V5A 1S6, Canada
| | - Scott G Hinch
- Pacific Salmon Ecology and Conservation Laboratory, Department of Forest and Conservation Sciences, The University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
| | - Erika J Eliason
- Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA, 93106-9620, USA
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Gamperl AK, Syme DA. Temperature effects on the contractile performance and efficiency of oxidative muscle from a eurythermal versus a stenothermal salmonid. J Exp Biol 2021; 224:jeb242487. [PMID: 34350949 PMCID: PMC8353165 DOI: 10.1242/jeb.242487] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2021] [Accepted: 05/24/2021] [Indexed: 01/18/2023]
Abstract
We compared the thermal sensitivity of oxidative muscle function between the eurythermal Atlantic salmon (Salmo salar) and the more stenothermal Arctic char (Salvelinus alpinus; which prefers cooler waters). Power output was measured in red skeletal muscle strips and myocardial trabeculae, and efficiency (net work/energy consumed) was measured for trabeculae, from cold (6°C) and warm (15°C) acclimated fish at temperatures from 2 to 26°C. The mass-specific net power produced by char red muscle was greater than in salmon, by 2-to 5-fold depending on test temperature. Net power first increased, then decreased, when the red muscle of 6°C-acclimated char was exposed to increasing temperature. Acclimation to 15°C significantly impaired mass-specific power in char (by ∼40-50%) from 2 to 15°C, but lessened its relative decrease between 15 and 26°C. In contrast, maximal net power increased, and then plateaued, with increasing temperature in salmon from both acclimation groups. Increasing test temperature resulted in a ∼3- to 5-fold increase in maximal net power produced by ventricular trabeculae in all groups, and this effect was not influenced by acclimation temperature. Nonetheless, lengthening power was higher in trabeculae from warm-acclimated char, and char trabeculae could not contract as fast as those from salmon. Finally, the efficiency of myocardial net work was approximately 2-fold greater in 15°C-acclimated salmon than char (∼15 versus 7%), and highest at 20°C in salmon. This study provides several mechanistic explanations as to their inter-specific difference in upper thermal tolerance, and potentially why southern char populations are being negatively impacted by climate change.
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Affiliation(s)
- A. Kurt Gamperl
- Department of Ocean Sciences, Memorial University of Newfoundland, St John's, NL, CanadaA1C 5S7
| | - Douglas A. Syme
- Department of Biological Sciences, University of Calgary, Calgary, AB, CanadaT2N 1N4
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3
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Driedzic WR. Low plasma glucose limits glucose metabolism by RBCs and heart in some species of teleosts. Comp Biochem Physiol B Biochem Mol Biol 2017; 224:204-209. [PMID: 28803129 DOI: 10.1016/j.cbpb.2017.08.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2017] [Revised: 08/02/2017] [Accepted: 08/03/2017] [Indexed: 12/28/2022]
Abstract
Within teleosts there is a species range in plasma glucose levels from undetectable to 20mM. At low plasma glucose levels the gradient from the extracellular to the intracellular space is decreased. The impact of this on glucose metabolism by RBCs and heart from species with different steady state levels of plasma glucose (Atlantic cod ~5mM; Atlantic salmon ~5mM, cunner ~1mM, lumpfish <1mM; short-horned sculpin <1mM) is the subject of this review. Under normoxia, at physiological levels of extracellular glucose, RBCs and heart produce lactate although the contribution of anaerobic metabolism to ATP production is small. Sustained lactate production from extracellular glucose appears to be the primary fate of extracellular glucose. In many cases, glycogen is not mobilized and the rate of glucose metabolism=two times the rate of lactate production. As such, alternative metabolic sources are required to fuel oxidative metabolism. Under hypoxia, hearts from Atlantic cod and rainbow trout increase rates of both glucose metabolism and lactate production, partially supported by glycogen reserves. But in lumpfish and short-horned sculpin hearts there is no change in rates of glucose metabolism. The most likely explanation is that glucose uptake is compromised in lumpfish and short-horned sculpin hearts due to a low diffusion gradient. Under these conditions rates of lactate production are well below that of Atlantic cod or rainbow trout. Energy demand must be reduced under hypoxia in lumpfish and short-horned sculpin hearts in order to maintain ATP balance.
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Affiliation(s)
- William R Driedzic
- Department of Ocean Sciences, Memorial University, St. John's, N.L. A1C 1S7, Canada.
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Clow KA, Short CE, Driedzic WR. Low levels of extracellular glucose limit cardiac anaerobic metabolism in some species of fish. ACTA ACUST UNITED AC 2017; 220:2970-2979. [PMID: 28596211 DOI: 10.1242/jeb.159582] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2017] [Accepted: 06/02/2017] [Indexed: 11/20/2022]
Abstract
There is a wide interspecific range in plasma glucose levels in teleosts from less than 0.5 to greater than 10 mmol l-1 Here we assessed how glucose availability influences glucose metabolism in hearts of Atlantic cod (Gadus morhua), rainbow trout (Oncorhynchus mykiss), lumpfish (Cyclopterus lumpus) and short-horned sculpin (Myoxocephalus scorpius) under normoxic and hypoxic conditions. These species had plasma glucose levels of 5.1, 4.8, 0.9 and 0.5 mmol l-1, respectively. Rates of glucose metabolism and lactate production were determined in isolated hearts perfused with medium containing physiological levels of glucose. Under normoxic conditions there was no significant difference in rates of either glucose metabolism (average 15 nmol g-1 min-1) or lactate production (average 30 nmol g-1 min-1) across species. Under hypoxia (12% of air saturation) there were significant increases in rates of glucose metabolism and lactate production in hearts from Atlantic cod (glucose-130; lactate-663 nmol g-1 min-1) and rainbow trout (glucose-103; lactate-774 nmol g-1 min-1); however, there was no change in rate of glucose metabolism in hearts from either lumpfish or short-horned sculpin and only increases in lactate production to rates much lower than the other species. Furthermore, Atlantic cod hearts perfused with medium containing low non-physiological levels of glucose (0.5 mmol l-1) had the same rates of glucose metabolism under normoxic and hypoxic treatments. Anaerobic metabolism supported by extracellular glucose is compromised in fish with low levels of plasma glucose, which in turn may decrease performance under oxygen-limiting conditions at the whole-animal level.
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Affiliation(s)
- Kathy A Clow
- Department of Ocean Sciences, Ocean Sciences Centre, Memorial University of Newfoundland, St. John's, NL A1C 5S7, Canada
| | - Connie E Short
- Department of Ocean Sciences, Ocean Sciences Centre, Memorial University of Newfoundland, St. John's, NL A1C 5S7, Canada
| | - William R Driedzic
- Department of Ocean Sciences, Ocean Sciences Centre, Memorial University of Newfoundland, St. John's, NL A1C 5S7, Canada
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Ekström A, Axelsson M, Gräns A, Brijs J, Sandblom E. Influence of the coronary circulation on thermal tolerance and cardiac performance during warming in rainbow trout. Am J Physiol Regul Integr Comp Physiol 2017; 312:R549-R558. [DOI: 10.1152/ajpregu.00536.2016] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2016] [Revised: 02/16/2017] [Accepted: 02/17/2017] [Indexed: 11/22/2022]
Abstract
Thermal tolerance in fish may be related to an oxygen limitation of cardiac function. While the hearts of some fish species receive oxygenated blood via a coronary circulation, the influence of this oxygen supply on thermal tolerance and cardiac performance during warming remain unexplored. Here, we analyzed the effect in vivo of acute warming on coronary blood flow in adult sexually mature rainbow trout ( Onchorhynchus mykiss) and the consequences of chronic coronary ligation on cardiac function and thermal tolerance in juvenile trout. Coronary blood flow at 10°C was higher in females than males (0.56 ± 0.08 vs. 0.30 ± 0.08 ml·min−1·g ventricle−1), and averaged 0.47 ± 0.07 ml·min−1·g ventricle−1 across sexes. Warming increased coronary flow in both sexes until 14°C, at which it peaked and plateaued at 0.78 ± 0.1 and 0.61 ± 0.1 ml·min−1·g ventricle−1 in females and males, respectively. Thus, the scope for increasing coronary flow was 101% in males, but only 39% in females. Coronary-ligated juvenile trout exhibited elevated heart rate across temperatures, reduced Arrhenius breakpoint temperature for heart rate (23.0 vs. 24.6°C), and reduced upper critical thermal maximum (25.3 vs. 26.3°C). To further analyze the effects of coronary flow restriction on cardiac rhythmicity, electrocardiogram characteristics were determined before and after coronary occlusion in anesthetized trout. Occlusion resulted in reduced R-wave amplitude and an elevated S-T segment, indicating myocardial ischemia, while heart rate was unaffected. This suggests that the tachycardia in ligated trout across temperatures in vivo was mainly to compensate for reduced cardiac contractility to maintain cardiac output. Moreover, our findings show that coronary flow increases with warming in a sex-specific manner. This may improve whole animal thermal tolerance, presumably by sustaining cardiac oxygenation and contractility at high temperatures.
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Affiliation(s)
- Andreas Ekström
- Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden; and
| | - Michael Axelsson
- Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden; and
| | - Albin Gräns
- Department of Animal Environment and Health, Swedish University of Agricultural Sciences, Skara, Sweden
| | - Jeroen Brijs
- Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden; and
| | - Erik Sandblom
- Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden; and
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Cox GK, Brill RW, Bonaro KA, Farrell AP. Determinants of coronary blood flow in sandbar sharks, Carcharhinus plumbeus. J Comp Physiol B 2016; 187:315-327. [PMID: 27678513 DOI: 10.1007/s00360-016-1033-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2016] [Revised: 09/05/2016] [Accepted: 09/13/2016] [Indexed: 11/28/2022]
Abstract
The coronary circulation first appeared in the chordate lineage in cartilaginous fishes where, as in birds and mammals but unlike most teleost fishes, it supplies arterial blood to the entire myocardium. Despite the pivotal position of elasmobranch fishes in the evolution of the coronary circulation, the determinants of coronary blood flow have never been investigated in this group. Elasmobranch fishes are of special interest because of the morphological arrangement of their cardiomyocytes. Unlike teleosts, the majority of the ventricular myocardium in elasmobranch fishes is distant to the venous blood returning to the heart (i.e., the luminal blood). Also, the majority of the myocardium is in close association with the coronary circulation. To determine the relative contribution of the coronary and luminal blood supplies to cardiovascular function in sandbar sharks, Carcharhinus plumbeus, we measured coronary blood flow while manipulating cardiovascular status using acetylcholine and adrenaline. By exploring inter- and intra-individual variation in cardiovascular variables, we show that coronary blood flow is directly related to heart rate (R 2 = 0.6; P < 0.001), as it is in mammalian hearts. Since coronary blood flow is inversely related to coronary resistance both in vivo and in vitro, we suggest that in elasmobranch fishes, changes in heart rate mediate changes in coronary vascular resistance, which adjust coronary blood flow appropriately.
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Affiliation(s)
- Georgina K Cox
- Department of Zoology, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada.
| | - Richard W Brill
- National Marine Fisheries Service, Northeast Fisheries Science Center, James J. Howard Marine Sciences Laboratory, Highlands, NJ, USA
| | | | - Anthony P Farrell
- Department of Zoology, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada.,Faculty of Land and Food Systems, University of British Columbia, Vancouver, BC, Canada
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Clow KA, Short CE, Driedzic WR. Extracellular glucose supports lactate production but not aerobic metabolism in cardiomyocytes from both normoglycemic Atlantic cod and low glycemic short-horned sculpin. ACTA ACUST UNITED AC 2016; 219:1384-93. [PMID: 26944490 DOI: 10.1242/jeb.132720] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Accepted: 02/23/2016] [Indexed: 01/26/2023]
Abstract
Fish exhibit a wide range of species-specific blood glucose levels. How this relates to glucose utilization is yet to be fully realized. Here, we assessed glucose transport and metabolism in myocytes isolated from Atlantic cod (Gadus morhua) and short-horned sculpin (Myoxocephalus scorpius), species with blood glucose levels of 3.7 and 0.57 mmol l(-1), respectively. Glucose metabolism was assessed by the production of (3)H2O from [2-(3)H]glucose. Glucose metabolism was 3.5- to 6-fold higher by myocytes from Atlantic cod than by those from short-horned sculpin at the same level of extracellular glucose. In Atlantic cod myocytes, glucose metabolism displayed what appears to be a saturable component with respect to extracellular glucose, and cytochalasin B inhibited glucose metabolism. These features revealed a facilitated glucose diffusion mechanism that accounts for between 30% and 55% of glucose entry at physiological levels of extracellular glucose. Facilitated glucose diffusion appears to be minimal in myocytes for short-horned sculpin. Glucose entry by simple diffusion occurs in both cell types with the same linear relationship between glucose metabolism and extracellular glucose concentration, presumably due to similarities in membrane composition. Oxygen consumption by myocytes incubated in medium containing physiological levels of extracellular glucose (Atlantic cod 5 mmol l(-1), short-horned sculpin 0.5 mmol l(-1)) was similar in the two species and was not decreased by cytochalasin B, suggesting that these cells have the capability of oxidizing alternative on-board metabolic fuels. Cells produced lactate at low rates but glycogen levels did not change during the incubation period. In cells from both species, glucose utilization assessed by both simple chemical analysis of glucose disappearance from the medium and (3)H2O production was half the rate of lactate production and as such extracellular glucose was not available for oxidative metabolism. Overall, extracellular glucose makes only a minor contribution to ATP production but a sustained glycolysis may be necessary to support Ca(2+) transport mechanisms at either the sarcoplasmic reticulum or the sarcolemmal membrane.
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Affiliation(s)
- Kathy A Clow
- Department of Ocean Sciences, Ocean Sciences Centre, Memorial University of Newfoundland, St John's, NL, Canada A1C 5S7
| | - Connie E Short
- Department of Ocean Sciences, Ocean Sciences Centre, Memorial University of Newfoundland, St John's, NL, Canada A1C 5S7
| | - William R Driedzic
- Department of Ocean Sciences, Ocean Sciences Centre, Memorial University of Newfoundland, St John's, NL, Canada A1C 5S7
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Becker TA, DellaValle B, Gesser H, Rodnick KJ. Limited effects of exogenous glucose during severe hypoxia and a lack of hypoxia-stimulated glucose uptake in isolated rainbow trout cardiac muscle. ACTA ACUST UNITED AC 2013; 216:3422-32. [PMID: 23685969 DOI: 10.1242/jeb.085688] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We examined whether exogenous glucose affects contractile performance of electrically paced ventricle strips from rainbow trout under conditions known to alter cardiomyocyte performance, ion regulation and energy demands. Physiological levels of d-glucose did not influence twitch force development for aerobic preparations (1) paced at 0.5 or 1.1 Hz, (2) at 15 or 23°C, (3) receiving adrenergic stimulation or (4) during reoxygenation with or without adrenaline after severe hypoxia. Contractile responses to ryanodine, an inhibitor of Ca(2+) release from the sarcoplasmic reticulum, were also not affected by exogenous glucose. However, glucose did attenuate the fall in twitch force during severe hypoxia. Glucose uptake was assayed in non-contracting ventricle strips using 2-[(3)H] deoxy-d-glucose (2-DG) under aerobic and hypoxic conditions, at different incubation temperatures and with different inhibitors. Based upon a lack of saturation of 2-DG uptake and incomplete inhibition of uptake by cytochalasin B and d-glucose, 2-DG uptake was mediated by a combination of facilitated transport and simple diffusion. Hypoxia stimulated lactate efflux sixfold to sevenfold with glucose present, but did not increase 2-DG uptake or reduce lactate efflux in the presence of cytochalasin B. Increasing temperature (14 to 24°C) also did not increase 2-DG uptake, but decreasing temperature (14 to 4°C) reduced 2-DG uptake by 45%. In conclusion, exogenous glucose improves mechanical performance under hypoxia but not under any of the aerobic conditions applied. The extracellular concentration of glucose and cold temperature appear to determine and limit cardiomyocyte glucose uptake, respectively, and together may help define a metabolic strategy that relies predominantly on intracellular energy stores.
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Affiliation(s)
- Tracy A Becker
- Department of Biological Sciences, Idaho State University, Pocatello, ID 83209-8007, USA
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Harwood CL, Young IS, Altringham JD. How the efficiency of rainbow trout (Oncorhynchus mykiss) ventricular muscle changes with cycle frequency. J Exp Biol 2002; 205:697-706. [PMID: 11907059 DOI: 10.1242/jeb.205.5.697] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARYDifferent species of animals require different cardiac performance and, in turn, their cardiac muscle exhibits different properties. A comparative approach can reveal a great deal about the mechanisms underlying myocardial contraction. Differences in myocardial Ca2+ handling between fish and mammals suggest a greater energy cost of activation in fish. Further, while there is considerable evidence that heart rate (or cycle frequency) should have a profound effect on the efficiency of teleost cardiac muscle, this effect has been largely overlooked. We set out to determine how cycle frequency affects the power output and efficiency of rainbow trout (Oncorhynchus mykiss) ventricular muscle and to relate this to the heart’s function in life. We measured power output and the rate of oxygen consumption (V̇O2) and then calculated efficiency over a physiologically realistic range of cycle frequencies.In contrast to mammalian cardiac muscle, in which V̇O2 increases with increasing heart rate, we found no significant change in V̇O2 in the teleost. However, power output increased by 25 % as cycle frequency was increased from 0.6 to 1.0 Hz, so net and total efficiency increased. A maximum total efficiency of 20 % was achieved at 0.8 Hz, whereas maximum power output occurred at 1.0 Hz. We propose that, since the heart operates continuously, high mechanical efficiency is a major adaptive advantage, particularly at lower heart rates corresponding to the more commonly used slower, sustainable swimming speeds. Efficiency was lower at the higher heart rates required during very fast swimming, which are used during escape or prey capture.If a fixed amount of Ca2+ is released and then resequestered each time the muscle is activated, the activation cost should increase with frequency. We had anticipated that this would have a large effect on the total energy cost of contraction. However, since V̇O2 remains constant, less oxygen is consumed per cycle at high frequencies. We suggest that a constant V̇O2 would be observed if the amount of activator Ca2+ were to decrease with frequency. This decrease in activation energy is consistent with the decrease in the systolic intracellular Ca2+ ([Ca2+]i) transient with increasing stimulation frequency seen in earlier studies.
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Davidson GW, Davie PS. Mechanical efficiency of isolated in situ perfused hearts of the eel Anguilla australis. Comp Biochem Physiol A Mol Integr Physiol 2001; 128:167-75. [PMID: 11137449 DOI: 10.1016/s1095-6433(00)00288-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Administration of exogenous Ach to isolated in situ saline-perfused hearts of Anguilla australis via the perfusate, resulted in reduction in cardiac frequency (F). This reduction in F became significant at Ach concentrations of 10(-11) M or greater. A weak inotropic effect of Ach at the lowest concentration tested (10(-13) M) was also observed. Maximum power output of preparations was 2.94+/-0.26 mW gVM(-1). The mechanical efficiency of A. australis hearts working at 25 and 50% of maximum power under different conditions of stroke volume (SV) and F was investigated. Cardiac frequency was manipulated using a combination of temperature and Ach administration. Stroke volume was manipulated by regulating input pressure of the perfusate supplying the preparations (pre-load). Values of MEF from preparations generating flow under conditions of low F/ high SV (treated with Ach 10(-7) M) were significantly greater than under conditions of high F/ low SV (untreated). The MEF of preparations appears to be related to inotropic state. The negative inotropy and increased mechanical efficiency produced by Ach appears to be the opposite of the so-called 'oxygen-wasting' effect produced by the positive inotropic agents, the catecholamines. This effect of Ach may be related to the dependence of teleost myocardium on extracellular Ca(2+) for excitation-contraction coupling during the cardiac cycle.
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Affiliation(s)
- G W Davidson
- Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Private Bag 11222, Palmerston North, New Zealand.
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Abstract
Vertebrate lungs have long been thought to have evolved in fishes largely as an adaptation for life in hypoxic water. This view overlooks the possibility that lungs may have functioned to supply the heart with oxygen and may continue to serve this function in extant fishes. The myocardium of most vertebrates is avascular and obtains oxygen from luminal blood. Because oxygen-rich pulmonary blood mixes with oxygen-poor systemic blood before entering the heart of air-breathing fishes, lung ventilation may supply the myocardium with oxygen and expand aerobic exercise capabilities. Although sustained exercise in tetrapods is facilitated by septation of the heart and the formation of a dual pressure system, a divided cardio-pulmonary system may conflict with myocardial oxygenation because the right side of the heart is isolated from pulmonary oxygen. This may have contributed to the evolution of the coronary circulation.
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Affiliation(s)
- C G Farmer
- Department of Ecology and Evolutionary Biology, University of California at Irvine 92697, USA.
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Isolated perfused fish hearts. ACTA ACUST UNITED AC 1994. [DOI: 10.1016/b978-0-444-82033-4.50017-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Davie PS, Franklin CE. Myocardial oxygen consumption and mechanical efficiency of a perfused dogfish heart preparation. J Comp Physiol B 1992; 162:256-62. [PMID: 1613164 DOI: 10.1007/bf00357532] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Oxygen consumption of an in-pericardium heart preparation from the spiny dogfish (Squalus acanthias) was linearly related to cardiac power output. Basal oxygen consumption, predicted from the regression, was 0.127 microliters.s-1.g ventricle mass-1 and increased by 0.189 microliters.s-1.g ventricle mass-1 per milliwatt of power generated. From the relationship between cardiac power output and mechanical efficiency, mechanical efficiency was predicted to increase with cardiac power output to a maximum of 21%. Mechanical efficiency was measured during volume loading and pressure loading at two power outputs (50% and 72% of maximum power output). At 50% of maximum power output, mechanical efficiency increased significantly by 2.87%, from 11.9 +/- 0.3% to 14.8 +/- 0.5% (n = 7), when flow was halved and output pressure doubled to achieve the same power output. Similarly, at 72% of maximum power output, mechanical efficiency increased from 14.74 +/- 0.92% to 17.61 +/- 0.84% (n = 6) when flow was halved and output pressure doubled to generate the same higher level of power output. The increased mechanical efficiency at higher output pressures is believed to result from cardiac myocytes working within a length range where they are able to generate the most tension during contraction and are most efficient. We speculate that the loss of mechanical efficiency associated with large changes in sarcomere length, when stroke volume is large, is a driving force behind the use of frequency as the principal means of increasing cardiac output as observed in more active fishes, birds and mammals.
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Affiliation(s)
- P S Davie
- Department of Physiology and Anatomy, Massey University, Palmerston North, New Zealand
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Cardiac Energy Metabolism. ACTA ACUST UNITED AC 1992. [DOI: 10.1016/s1546-5098(08)60335-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/26/2023]
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Farrell AP, Steffensen JF. Coronary ligation reduces maximum sustained swimming speed in Chinook salmon, Oncorhynchus tshawytscha. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. A, COMPARATIVE PHYSIOLOGY 1987; 87:35-7. [PMID: 2886259 DOI: 10.1016/0300-9629(87)90421-x] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The maximum aerobic swimming speed of Chinook salmon (Oncorhynchus tshawytscha) was measured before and after ligation of the coronary artery. Coronary artery ligation prevented blood flow to the compact layer of the ventricular myocardium, which represents 30% of the ventricular mass, and produced a statistically significant 35.5% reduction in maximum swimming speed. We conclude that the coronary circulation is important for maximum aerobic swimming and implicit in this conclusion is that maximum cardiac performance is probably necessary for maximum aerobic swimming performance.
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17
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Driedzic WR, Gesser H. Ca2+ protection from the negative inotropic effect of contraction frequency on teleost hearts. J Comp Physiol B 1985. [DOI: 10.1007/bf00692936] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Relationship between exogenous fuel availability and performance by teleost and elasmobranch hearts. J Comp Physiol B 1984. [DOI: 10.1007/bf00684413] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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