Isovolumetric performance of isolated ground squirrel and rat hearts at low temperature

1984 ◽  
Vol 247 (4) ◽  
pp. R722-R727 ◽  
Author(s):  
D. R. Caprette ◽  
J. B. Senturia
Keyword(s):  
Low Temperature ◽  
Ground Squirrel ◽  
Mechanical Performance ◽  
Cell Communication ◽  
Ventricular Myocardium ◽  
Ground Squirrels ◽  
Rat Hearts ◽  
Pulsus Alternans ◽  
Rate Of Increase ◽  
Developed Pressure

The effects of low temperature on mechanical performance of the isolated left ventricles of the 13-lined ground squirrel (a hibernator) and the rat (a nonhibernator) were studied. In addition, low-temperature performance of hearts from summer-active, winter-hibernating, and winter-active ground squirrels were compared. By measuring pressure (P) generated against a balloon inserted into the left ventricle, maximum developed pressure (DP) and maximum rate of increase of P (peak dP/dt) were determined over a temperature range of 5–20 degrees C. The DP and dP/dt of the rat ventricle exhibited significantly greater reduction in magnitude at reduced temperature, compared with those of ground squirrel ventricle. Rat, but not ground squirrel, hearts exhibited arrhythmias of various kinds, including extra-systoles, tachycardia, pulsus alternans, and periods of asystole. Hearts from winter-active ground squirrels developed greater pressures than those from winter-hibernating and summer-active animals. This evidence suggests that disruption of cell communication in the nonhibernator ventricular myocardium plays an important role in the failure of the nonhibernator heart at low body temperatures. Contractility of the seasonal hibernator's heart is influenced by both season and hibernation itself, possibly through shifts in myocardial metabolism. However, seasonal adaptations appear not to be required to confer the special resistance of the seasonal hibernator's heart to the deleterious effects of low temperature.

Pancreatic triacylglycerol lipase in a hibernating mammal. II. Cold-adapted function and differential expression

2003 ◽  
Vol 16 (1) ◽  
pp. 131-140 ◽  
Author(s):  
Teresa L. Squire ◽  
Mark E. Lowe ◽  
Vernon W. Bauer ◽  
Matthew T. Andrews
Keyword(s):  
Low Temperature ◽  
High Activity ◽  
Ground Squirrel ◽  
Mammalian Cells ◽  
Lipolytic Activity ◽  
Tissue Expression ◽  
Ground Squirrels ◽  
Mrna Levels ◽  
Western Blots ◽  
Triacylglycerol Lipase

Thirteen-lined ground squirrels ( Spermophilus tridecemlineatus) exploit the low-temperature activity of pancreatic triacylglycerol lipase (PTL) during hibernation. Lipolytic activity at body temperatures associated with hibernation was examined using recombinant ground squirrel and human PTLs expressed in yeast. Both the human and ground squirrel enzymes displayed high activity at temperatures as low as 0°C and showed Q10 values of 1.2–1.5 over a range of 37–7°C. These studies indicate that low-temperature lipolysis is a general property of PTL and does not require protein modifications unique to mammalian cells and/or the hibernating state. Western blots show elevated levels of PTL protein during hibernation in both heart and white adipose tissue (WAT). Significant increases in PTL gene expression are seen in heart, WAT, and testes; but not in pancreas, where PTL mRNA levels are highest. Upregulation of PTL in testes is also accompanied by expression of the PTL-specific cofactor, colipase. The multi-tissue expression of PTL during hibernation supports its role as a key enzyme that shows high activity at low temperatures.

Effect of perfusate Ca2+ on the relation between metabolism and mechanical performance in the rat heart

1980 ◽  
Vol 58 (5) ◽  
pp. 570-573 ◽  
Author(s):  
T. Russell Snow ◽  
Gabor Rubanyi ◽  
Tunde Dora ◽  
Eörs Dora ◽  
Arisztid G. B. Kovach
Keyword(s):  
Respiratory Chain ◽  
Mechanical Performance ◽  
Left Ventricular ◽  
Perfused Heart ◽  
Exogenous Substrate ◽  
Rat Hearts ◽  
Nadh Fluorescence ◽  
Perfused Rat Hearts ◽  
Developed Pressure ◽  
Contractile Performance

Langendorf perfused rat hearts (n = 25) were used to study the effects of changes in perfusate Ca2+ concentration ([Ca2+p]) on the relation between metabolism and mechanical performance with either glucose or pyruvate as the exogenous substrate. Increased [Ca2+p] (from 1.3 to 3.9 mM) produced an increase (243 ± 38%) in left ventricular developed pressure regardless of the substrate. With glucose as the substrate, the NADH fluorescence intensity increased by 11.8 ± 1.2% (n = 17) relative to control indicating a more reduced state of the respiratory chain. Increasing [Ca2+p] in the pyruvate perfused heart produced the expected NADH oxidation (−6.2 ± 1.1%; n = 8). Hence the change in NADH fluorescence associated with increased [Ca2+p] is substrate dependent. The data show that, with glucose as the substrate but not with pyruvate, increases in [Ca2+p] increase the availability of reducing equivalents to the respiratory chain above the level necessary to compensate for the increased demand resulting from the greater contractile performance.

Genes controlling the metabolic switch in hibernating mammals

2004 ◽  
Vol 32 (6) ◽  
pp. 1021-1024 ◽  
Author(s):  
M.T. Andrews
Keyword(s):  
Low Temperature ◽  
Pyruvate Dehydrogenase ◽  
Ground Squirrel ◽  
Mammalian Cells ◽  
Lipolytic Activity ◽  
Tricarboxylic Acid Cycle ◽  
Ground Squirrels ◽  
Pyruvate Dehydrogenase Kinase ◽  
Body Temperatures ◽  
Triacylglycerol Lipase

Hibernating mammals have the ability to decrease their metabolic rate and survive up to 6 months without food in an inactive state where body temperatures approach 0°C. In hibernating 13-lined ground squirrels (Spermophilus tridecemlineatus), oxygen consumption holds at 1/30 to 1/50 of the aroused condition and heart rates are as low as 3–10 beats/min, compared with 200–300 beats/min when the animal is active. This seasonal adaptation requires a metabolic shift away from the oxidation of carbohydrates and towards the combustion of stored fatty acids as the primary source of energy. A key element in this fuel switch is the differential expression of the gene encoding pyruvate dehydrogenase kinase isoenzyme 4. Pyruvate dehydrogenase kinase isoenzyme 4 inhibits pyruvate dehydrogenase and thus minimizes carbohydrate oxidation by preventing the flow of glycolytic products into the tricarboxylic acid cycle. Hibernators also exploit the low-temperature activity of PTL (pancreatic triacylglycerol lipase) in both heart and white adipose tissue. Lipolytic activity at body temperatures associated with hibernation was examined using recombinant ground squirrel and human PTL expressed in yeast. Enzymes from both humans and ground squirrel displayed high activity at temperatures as low as 0°C and showed Q10=1.2–1.5 over the temperature range 37–7°C. These studies indicate that low-temperature lipolysis is a general property of PTL and does not require protein modifications unique to mammalian cells and/or the hibernating state.

scholarly journals How apparent competition and predator responses led to the decline of Arctic ground squirrels in the boreal forests of the southwest Yukon

2016 ◽  
Author(s):  
Jeffery R Werner ◽  
Elizabeth A Gillis ◽  
Rudy Boonstra ◽  
Charles J Krebs
Keyword(s):  
Ground Squirrel ◽  
Boreal Forests ◽  
Apparent Competition ◽  
Ground Squirrels ◽  
Critical Threshold ◽  
Snowshoe Hare ◽  
Sympatric Populations ◽  
Population Growth Rates ◽  
Rate Of Increase ◽  
Arctic Ground Squirrels

Throughout much of North America’s boreal forest, the cyclical fluctuations of snowshoe hare populations (Lepus americanus) may cause other herbivores to become entrained in similar cycles. Alternating apparent competition and indirect mutualism via prey switching are the mechanisms behind this interaction. Our purpose is to document a change in the role of indirect interactions between sympatric populations of hares and arctic ground squirrels (Urocitellus parryii plesius), and to emphasize the influence of predation for controlling ground squirrel numbers. We used mark-recapture to estimate the population densities of both species over a 25-year period that covered two snowshoe hare cycles. We analysed the strength of association between snowshoe hare and ground squirrel numbers and changes in the seasonal and annual population growth rates of ground squirrels over time. A hyperbolic curve best describes the per capita rate of increase of ground squirrels relative to their population size, with a single stable equilibrium and a lower critical threshold below which populations drift to extinction. The crossing of this unstable boundary resulted in the subsequent uncoupling of ground squirrel and hare populations following the decline phase of their cycles in 1998. The implications are that this sustained Type II predator response led to the local extinction of ground squirrels. Arctic ground squirrels may also have exhibited an Allee effect caused by the disruption of social signalling of approaching predators when few individuals are left in a colony.

scholarly journals Effects of hypothermia on energy metabolism in rat and Richardson’s ground squirrel hearts

1997 ◽  
Vol 82 (4) ◽  
pp. 1210-1218 ◽  
Author(s):  
Darrell D. Belke ◽  
Lawrence C. H. Wang ◽  
Gary D. Lopaschuk
Keyword(s):  
Energy Metabolism ◽  
Functional Recovery ◽  
Ground Squirrel ◽  
Ground Squirrels ◽  
General Effect ◽  
Energy Substrate ◽  
Substrate Metabolism ◽  
Hypothermic Perfusion ◽  
Rat Hearts ◽  
The Difference

Belke, Darrell D., Lawrence C. H. Wang, and Gary D. Lopaschuk. Effects of hypothermia on energy metabolism in rat and Richardson’s ground squirrel hearts. J. Appl. Physiol. 82(4): 1210–1218, 1997.—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°C, followed by 2 h of hypothermic perfusion at 15°C, after which hearts were rewarmed to 37°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.

scholarly journals You can hide but you can’t run: apparent competition, predator responses and the decline of Arctic ground squirrels in boreal forests of the southwest Yukon

PeerJ ◽  
2016 ◽  
Vol 4 ◽  
pp. e2303 ◽  
Author(s):  
Jeffery R. Werner ◽  
Elizabeth A. Gillis ◽  
Rudy Boonstra ◽  
Charles J. Krebs
Keyword(s):  
Ground Squirrel ◽  
Boreal Forests ◽  
Apparent Competition ◽  
Ground Squirrels ◽  
Critical Threshold ◽  
Snowshoe Hare ◽  
Sympatric Populations ◽  
Population Growth Rates ◽  
Rate Of Increase ◽  
Arctic Ground Squirrels

Throughout much of North America’s boreal forest, the cyclical fluctuations of snowshoe hare populations (Lepus americanus) may cause other herbivores to become entrained in similar cycles. Alternating apparent competition via prey switching followed by positive indirect effects are the mechanisms behind this interaction. Our purpose is to document a change in the role of indirect interactions between sympatric populations of hares and arctic ground squirrels (Urocitellus parryii plesius), and to emphasize the influence of predation for controlling ground squirrel numbers. We used mark-recapture to estimate the population densities of both species over a 25-year period that covered two snowshoe hare cycles. We analysed the strength of association between snowshoe hare and ground squirrel numbers, and the changes to the seasonal and annual population growth rates of ground squirrels over time. A hyperbolic curve best describes the per capita rate of increase of ground squirrels relative to their population size, with a single stable equilibrium and a lower critical threshold below which populations drift to extinction. The crossing of this unstable boundary resulted in the subsequent uncoupling of ground squirrel and hare populations following the decline phase of their cycles in 1998. The implications are that this sustained Type II predator response led to the local extinction of ground squirrels. When few individuals are left in a colony, arctic ground squirrels may also have exhibited an Allee effect caused by the disruption of social signalling of approaching predators.

scholarly journals How apparent competition and predator responses led to the decline of Arctic ground squirrels in the boreal forests of the southwest Yukon

2016 ◽  
Author(s):  
Jeffery R Werner ◽  
Elizabeth A Gillis ◽  
Rudy Boonstra ◽  
Charles J Krebs
Keyword(s):  
Ground Squirrel ◽  
Boreal Forests ◽  
Apparent Competition ◽  
Ground Squirrels ◽  
Critical Threshold ◽  
Snowshoe Hare ◽  
Sympatric Populations ◽  
Population Growth Rates ◽  
Rate Of Increase ◽  
Arctic Ground Squirrels

Throughout much of North America’s boreal forest, the cyclical fluctuations of snowshoe hare populations (Lepus americanus) may cause other herbivores to become entrained in similar cycles. Alternating apparent competition and indirect mutualism via prey switching are the mechanisms behind this interaction. Our purpose is to document a change in the role of indirect interactions between sympatric populations of hares and arctic ground squirrels (Urocitellus parryii plesius), and to emphasize the influence of predation for controlling ground squirrel numbers. We used mark-recapture to estimate the population densities of both species over a 25-year period that covered two snowshoe hare cycles. We analysed the strength of association between snowshoe hare and ground squirrel numbers and changes in the seasonal and annual population growth rates of ground squirrels over time. A hyperbolic curve best describes the per capita rate of increase of ground squirrels relative to their population size, with a single stable equilibrium and a lower critical threshold below which populations drift to extinction. The crossing of this unstable boundary resulted in the subsequent uncoupling of ground squirrel and hare populations following the decline phase of their cycles in 1998. The implications are that this sustained Type II predator response led to the local extinction of ground squirrels. Arctic ground squirrels may also have exhibited an Allee effect caused by the disruption of social signalling of approaching predators when few individuals are left in a colony.

Temperature and the Regulation of Enzyme Activity in the Hibernator. Isoenzymes of Liver Pyruvate Kinase from the Hibernating and Non-hibernating Arctic Ground Squirrel

1974 ◽  
Vol 52 (10) ◽  
pp. 894-902 ◽  
Author(s):  
Hans W. Behrisch
Keyword(s):  
Molecular Weight ◽  
Pyruvate Kinase ◽  
Wide Temperature Range ◽  
Ground Squirrel ◽  
Energy Charge ◽  
High Energy ◽  
Ground Squirrels ◽  
The Arctic ◽  
Arctic Ground Squirrel ◽  
Temperature Range

Liver of the hibernating (H) Arctic ground squirrel (Citellus undulatus) contains a single species of pyruvate kinase (PyK) that is distinct from the single isoenzyme of pyK observed in the non-hibernating (NH) ground squirrel, which has been previously described (Behrisch &Johnson (1974) Can. J. Biochem. 52, 547–559). The H-PyK has a pI value of 5.7 and a molecular weight of 241 000 – 243 000. Affinity of the H-PyK for the substrates phosphoenolpyruvate (PEP) and ADP is not affected by changing temperature. It is argued that this stability of the apparent Km's for substrate over a wide temperature range permits the hibernator to take advantage of the Q10 effect in maintaining a low rate of the PyK reaction. Similarly, affinity of H-PyK for the allosteric activator fructose-1,6-phosphate (FDP) and the inhibitor ATP is also conspicuously independent of temperature, suggesting a fine stoichiometry in the relative concentrations of the regulatory ligands in control of H-PyK over a wide temperature range. Further, affinity of H-PyK for the inhibitor ATP is about three- to fourfold lower than that of the NH-PyK, a condition that would favor the maintenance of a high energy charge in the hibernating liver cell. ATP apparently inhibits PyK by causing a dissociation of the enzyme molecule into two "halves" of about 110 000 molecular weight each. This dissociation is offset and reversed by FDP. Removal of the ATP by dialysis does not of itself result in a reassociation of the PyK "halves"; FDP and/or the substrates are required for the two subunits of PyK to reassociate. As the apparent Ki of H-PyK for ATP is higher than that of NH-PyK, substantially higher concentrations of ATP are required to effect the dissociation of H-PyK. Similarly, elevated concentrations of FDP are required to offset the ATP-caused dissociation of the H-PyK.Hibernating Arctic ground squirrels that are preparing to emerge finally from the hibernating state already possess substantial activities of the NH-PyK isoenzyme. This suggests that the animal "anticipates" its transition from one metabolic state from another. On the basis of these data a formal mechanism is proposed for the regulation of liver PyK in the Arctic ground squirrel in both the non-hibernating and hibernating states.

Abstract 1712: The P2Y 12 Antagonist Cangrelor and the GP IIb/IIIa Blocker Abciximab Reduce Platelet-Mediated Myocardial Injury After Ischemia and Reperfusion

Circulation ◽  
2008 ◽  
Vol 118 (suppl_18) ◽  
Author(s):  
Jose A Barrabes ◽  
Javier Inserte ◽  
Maribel Mirabet ◽  
Adoracion Quiroga ◽  
Victor Hernando ◽  
...  
Keyword(s):  
Myocardial Injury ◽  
Myocardial Damage ◽  
Left Ventricular ◽  
Myocardial Salvage ◽  
Ischemia And Reperfusion ◽  
Activated Platelets ◽  
Rat Hearts ◽  
Developed Pressure ◽  
Enddiastolic Pressure ◽  
Isolated Rat

Objective: Platelets activated during experimental acute myocardial infarction (AMI) contribute to myocardial injury. We aimed to investigate whether platelets from patients with AMI increase myocardial damage after transient ischemia in isolated rat hearts and the modification of this effect by the P2Y 12 receptor antagonist cangrelor and the GPIIb/IIIa receptor blocker abciximab. Methods: Platelets were obtained from 9 AMI patients (7 thrombolyzed, all on aspirin) within 24 h after symptom onset. Incubation with 100 μM cangrelor or 50 μg/ml abciximab resulted, respectively, in 78 ± 4 and 90 ± 2% inhibition of aggregation (optical aggregometry). Isolated rat hearts (four simultaneous experiments per patient) were subjected to 40 min of global ischemia and 60 min of reperfusion. Hearts received no additional intervention (Control) or were infused during the 5 min prior to ischemia with platelets (22.5x10 6 /min), either untreated or treated with cangrelor or abciximab. Results: P-selectin expression (flow cytometry) in isolated platelets before infusion was 31 ± 3% (P = NS between groups). Platelets augmented myocardial injury, as demonstrated by worse left ventricular developed pressure (LVDevP), higher left ventricular enddiastolic pressure (LVEDP) and coronary resistance, and greater LDH release and infarct size (TTC staining), and both cangrelor and abciximab greatly attenuated these effects (Table ). Conclusions: Activated platelets from patients with AMI increase myocardial injury after ischemia and reperfusion, and cangrelor and abciximab attenuate this effect. The results support the notion that very early antiplatelet treatment may increase myocardial salvage by direct effects on the microcirculation in these patients.

Correlation between myocardial contractile force and cytosolic inorganic phosphate during early ischemia

1997 ◽  
Vol 272 (3) ◽  
pp. H1333-H1341 ◽  
Author(s):  
M. X. He ◽  
S. Wang ◽  
H. F. Downey
Keyword(s):  
Inorganic Phosphate ◽  
Contractile Force ◽  
Left Ventricular ◽  
Resonance Spectroscopy ◽  
Rat Hearts ◽  
Initial Control ◽  
Myocardial Contractile Force ◽  
Myocardial Contractile ◽  
Developed Pressure

To test the role of inorganic phosphate (Pi) in downregulation of myocardial contractile force at the onset of ischemia, Pi of rat hearts was determined with 31P nuclear magnetic resonance spectroscopy. Forty cycles of brief hypoperfusion (30% of baseline flow for 33 s) were used to achieve a time resolution of 0.512 s for comparing dynamic changes in Pi and contractile force. Initial control values of left ventricular developed pressure (LVP), heart rate, and oxygen consumption were 136 +/- 11 mmHg, 236 +/- 4 beats/min, and 95 +/- 3 microl O2 x min(-1) x g(-1); these values were unchanged at the end of the experiment. During the first 10 s of hypoperfusion, Pi increased at a rate (percentage of the total observed change) faster than the decrease in LVP; Pi and LVP then changed at the same rate during the remainder of the hypoperfusion. ADP did not change in advance of LVP. Intracellular pH did not change. The results indicate that Pi plays an important role in initiating the downregulation of myocardial contractile force at the onset of ischemia. Perfusion pressure also declined faster than LVP at the onset of ischemia, indicating potential importance of vascular collapse in contractile downregulation during early ischemia.

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