The heart extrasystole: an energetic approach

1999 ◽  
Vol 276 (1) ◽  
pp. H309-H316 ◽  
Author(s):  
Fernando D. Marengo ◽  
María T. Márquez ◽  
Patricia Bonazzola ◽  
Jorge E. Ponce-Hornos
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Heat Release ◽  
Energetic Approach ◽  
Dependent Component ◽  
Pressure Development ◽  
Time Courses ◽  
Pressure Independent ◽  
Rat Ventricle ◽  
Heat Released ◽  
Text Component

The consequences of an extrasystole (ES) on cardiac muscle’s energetics and Ca2+ homeostasis were investigated in the beating heart. The fraction of heat release related to pressure development (pressure dependent) and pressure-independent heat release were measured during isovolumic contractions in arterially perfused rat ventricle. The heat release by a contraction showed two pressure-independent components (H1 and H2) of short evolution and a pressure-dependent component (H3). The additional heat released by ES was decomposed into one pressure-independent ([Formula: see text]) and one pressure-dependent ([Formula: see text]) component with time courses similar to those of control components H2 and H3. ES also induced the potentiation of pressure development (P) and heat release during the postextrasystolic (PES) beat. The slope of the linear relationship between pressure-dependent heat and pressure maintenance was similar in control, ES, and PES contractions (0.08 ± 0.01, 0.10 ± 0.02, and 0.08 ± 0.01 mJ ⋅ g−1 ⋅ mmHg−1 ⋅ s−1, respectively). The potentiation of H2 (heat component related with Ca2+ removal processes) in PES was equal to [Formula: see text] at 0.3, 0.5, 1, and 2 mM Ca2+, suggesting that the extra amount of Ca2+ mobilized during ES was recycled in PES. Pretreatment with 1 mM caffeine to deplete sarcoplasmic reticulum Ca2+ content inhibited both the mechanical and energetic potentiation of PES. However, the heat released and the pressure developed during ES were not changed by sarcoplasmic reticulum depletion. The results suggest that 1) the source of Ca2+ for ES would be entirely extracellular, 2) the Ca2+ entered during ES is accumulated in the sarcoplasmic reticulum, and 3) the Ca2+ stored by the sarcoplasmic reticulum during ES induces an increased contribution of this organelle during PES compared with the normal contraction.

Effects of caffeine, verapamil, lithium, and KB-R7943 on mechanics and energetics of rat myocardial bigeminies

2006 ◽  
Vol 290 (2) ◽  
pp. H613-H623 ◽  
Author(s):  
E. Savio-Galimberti ◽  
J. E. Ponce-Hornos
Keyword(s):  
Heat Release ◽  
Energetic Cost ◽  
Postextrasystolic Potentiation ◽  
Mechanical Responses ◽  
Time Integral ◽  
Pressure Time ◽  
Dependent Component ◽  
Pressure Development ◽  
Pressure Independent ◽  
Stimulation Pattern

We examined the effects of pharmacological alteration of Ca2+ sources on mechanical and energetic properties of paired-pulse (“bigeminic”) contractions. The fraction of heat release that is related to pressure development and pressure-independent heat release were measured during isovolumic contractions in arterially perfused rat ventricles. The heat released by regular and bigeminic contractions showed two brief pressure-independent components (H1 and H2) and a pressure-dependent component (H3). We used the ratio of active heat (H′a) to pressure-time integral (PtI) and the ratio of H3 to PtI to estimate the energetic cost of muscle contraction (overall economy) and pressure maintenance (contractile economy), respectively. Neither of these ratios was affected by stimulation pattern. Caffeine (an inhibitor of sarcoplasmic reticulum function) significantly decreased mechanical responses and increased the energetic cost of contraction (Δ = 101 ± 12.6%). Verapamil (an L-type Ca2+ channel blocker) decreased pressure maintenance of extrasystolic (Δ = 43.4 ± 3.7%) and postextrasystolic (Δ = 37.5 ± 3.5%) contractions without affecting postextrasystolic potentiation, suggesting that a verapamil-insensitive fraction is responsible for potentiation. The verapamil-insensitive fraction was further studied in the presence of lithium (45 mM) and KB-R7943 (5 μM), inhibitors of the Na+/Ca2+ exchanger. Both agents decreased all mechanical responses, including postextrasystolic potentiation (Δ = 67.3 ± 3.3%), without altering overall or contractile economies, suggesting an association of the verapamil-insensitive Ca2+ fraction to the sarcolemmal Na+/Ca2+ exchanger. The effect of the inhibitors of the Na+/Ca2+ exchanger on potentiation suggests an increased participation of extracellular Ca2+ (and, thus, a redistribution of the relative participation of the Ca2+ pools) during bigeminic contractions in rat myocardium.

scholarly journals Mathematical Analysis and Simulation of Ahrens Model in Pulse Combustor

2020 ◽  
Vol 9 (3S2) ◽  
pp. 10-13
Keyword(s):  
Mathematical Model ◽  
Heat Release ◽  
Mathematical Analysis ◽  
Large Data ◽  
System Stability ◽  
Cool Zone ◽  
Pulse Combustor ◽  
Specific Object ◽  
Pressure Independent ◽  
Heat Released

Ahrens model accepted large data of Kilicarslan but with some real differences. In Kilicarslan model, released heat in combustion having more I2R that is released under Ahrens. As per Ahrens if any specific object divides reaction and cool zone then heat release / cycle is very less compare with Kilicarslan. But with one condition of one object that is, it should be pressure independent otherwise density of reactants remains constant (or not enough increased); as a result, more heat released with less satisfied output. Mathematical model of Ahrens brief about object zones and its separation. This paper also brief about dynamic work function of tailpipe with adjustment of frequency which will proceed for system stability and its accuracy.

scholarly journals The Synergy of Two Biofuel Additives on Combustion Process to Simultaneously Reduce NOx and PM Emissions

Energies ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2784
Author(s):  
Jerzy Cisek ◽  
Szymon Lesniak ◽  
Winicjusz Stanik ◽  
Włodzimierz Przybylski
Keyword(s):  
Heat Release ◽  
Combustion Rate ◽  
Combustion Process ◽  
The Other ◽  
Fuel Additive ◽  
Exhaust Gas ◽  
Synergy Effect ◽  
Engine Exhaust ◽  
Other Hand ◽  
Heat Released

The article presents the results of research on the influence of two fuel additives that selectively affect the combustion process in a diesel engine cylinder. The addition of NitrON® reduces the concentration of nitrogen oxides (NOx), due to a reduction in the kinetic combustion rate, at the cost of a slight increase in the concentration of particulate matter (PM) in the engine exhaust gas. The Reduxco® additive reduces PM emissions by increasing the diffusion combustion rate, while slightly increasing the NOx concentration in the engine exhaust gas. Research conducted by the authors confirmed that the simultaneous use of both of these additives in the fuel not only reduced both NOx and PM emissions in the exhaust gas but additionally the reduction of NOx and PM emissions was greater than the sum of the effects of these additives—the synergy effect. Findings indicated that the waveforms of the heat release rate (dQ/dα) responsible for the emission of NOx and PM in the exhaust gas differed for the four tested fuels in relation to the maximum value (selectively and independently in the kinetic and diffusion stage), and they were also phase shifted. Due to this, the heat release process Q(α) was characterized by a lower amount of heat released in the kinetic phase compared to fuel with NitrON® only and a greater amount of heat released in the diffusion phase compared to fuel with Reduxco® alone, which explained the lowest NOx and PM emissions in the exhaust gas at that time. For example for the NOx concentration in the engine exhaust: the Nitrocet® fuel additive (in the used amount of 1500 ppm) reduces the NOx concentration in the exhaust gas by 18% compared to the base fuel. The addition of a Reduxco® catalyst to the fuel (1500 ppm) unfortunately increases the NOx concentration by up to 20%. On the other hand, the combustion of the complete tested fuel, containing both additives simultaneously, is characterized, thanks to the synergy effect, by the lowest NOx concentration (reduction by 22% in relation to the base). For example for PM emissions: the Nitrocet® fuel additive does not significantly affect the PM emissions in the engine exhaust (up to a few per cent compared to the base fuel). The addition of a Reduxco® catalyst to the fuel greatly reduces PM emissions in the engine exhaust, up to 35% compared to the base fuel. On the other hand, the combustion of the complete tested fuel containing both additives simultaneously is characterized by the synergy effect with the lowest PM emission (reduction of 39% compared to the base fuel).

Role of intracellular calcium and metabolites in low-frequency fatigue of mouse skeletal muscle

1997 ◽  
Vol 272 (2) ◽  
pp. C550-C559 ◽  
Author(s):  
E. R. Chin ◽  
C. D. Balnave ◽  
D. G. Allen
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Low Frequency ◽  
Single Muscle ◽  
Low Frequencies ◽  
Time Integral ◽  
Metabolic Component ◽  
Dependent Component ◽  
Low Frequency Fatigue

We have examined the extent to which prolonged reductions in low-frequency force (i.e., low-frequency fatigue) result from increases in intracellular free Ca2+ concentration ([Ca2+]i) and alterations in muscle metabolites. Force and [Ca2+]i were measured in mammalian single muscle fibers in response to short, intermediate, and long series of tetani that elevated the [Ca2+]i-time integral to 5, 17, and 29 microM x s, respectively. Only the intermediate and long series resulted in prolonged (>60 x min) reductions in Ca2+ release and low-frequency fatigue. When fibers recovered from the long series of tetani without glucose, Ca2+ release was reduced to a greater extent and force was reduced at high and low frequencies. These findings indicate that the decrease in sarcoplasmic reticulum Ca2+ release associated with fatigue has at least two components: 1) a metabolic component, which, in the presence of glucose, recovers within 1 h, and 2) a component dependent on the elevation of the [Ca2+]i-time integral, which recovers more slowly. It is this Ca2+-dependent component that is primarily responsible for low-frequency fatigue.

Role of the Sarcoplasmic Reticulum Ca2+-ATPase on Heat Production and Thermogenesis

2001 ◽  
Vol 21 (2) ◽  
pp. 113-137 ◽  
Author(s):  
Leopoldo de Meis
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Atp Hydrolysis ◽  
Surrounding Medium ◽  
Chemical Energy ◽  
The Past ◽  
Sarcoplasmic Reticulum Membrane ◽  
Membrane Bound ◽  
Hydrolysis Of ◽  
Heat Released

The sarcoplasmic reticulum of skeletal muscle retains a membrane bound Ca2+-ATPase which is able to interconvert different forms of energy. A part of the chemical energy released during ATP hydrolysis is converted into heat and in the bibliography it is assumed that the amount of heat produced during the hydrolysis of an ATP molecule is always the same, as if the energy released during ATP cleavage were divided in two non-interchangeable parts: one would be converted into heat, and the other used for Ca2+ transport. Data obtained in our laboratory during the past three years indicate that the amount of heat released during the hydrolysis of ATP may vary between 7 and 32 kcal/mol depending on whether or not a transmembrane Ca2+ gradient is formed across the sarcoplasmic reticulum membrane. Drugs such as heparin and dimethyl sulfoxide are able to modify the fraction of the chemical energy released during ATP hydrolysis which is used for Ca2+ transport and the fraction which is dissipated in the surrounding medium as heat.

scholarly journals Cytosolic free Ca2+ in single rat heart cells during anoxia and reoxygenation

1987 ◽  
Vol 244 (2) ◽  
pp. 381-385 ◽  
Author(s):  
A Allshire ◽  
H M Piper ◽  
K S Cuthbertson ◽  
P H Cobbold
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Rat Heart ◽  
Heart Cells ◽  
Free Medium ◽  
Rat Heart Cells ◽  
Rat Ventricle

Free Ca2+ in the cytosol ([Ca2+]i) of individual rat ventricle cells injected with aequorin was measured under anoxia. In glucose-free medium myocytes spontaneously shortened after about 60 min, although [Ca2+]i was still at or near resting levels. However, within minutes a net inward movement of Ca2+ across the sarcolemma developed and [Ca2+]i began to rise. Provided oxygen was readmitted before [Ca2+]i exceeded 2-3 microM, cells were able to restore [Ca2+]i to resting levels through caffeine-sensitive sequestration of Ca2+ in the sarcoplasmic reticulum. We suggest that Ca2+-independent shortening of anoxic cardiomyocytes reflects onset of rigor which triggers loss of [Ca2+]i homoeostasis.

scholarly journals Effect of MgO Content on Heat Capacity of Synthetic BF Slag and Heat Release Behavior during Cooling Process

Metals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1294
Author(s):  
Yanhua Yang ◽  
Ting Lei ◽  
Yuelin Qin
Keyword(s):  
Heat Capacity ◽  
Specific Heat ◽  
Heat Release ◽  
Specific Heat Capacity ◽  
Slag System ◽  
Cooling Process ◽  
Scanning Calorimetry ◽  
Bf Slag ◽  
Slag Cooling ◽  
Heat Released

The differential scanning calorimetry (DSC) sapphire analysis was used to measure the specific heat capacity of the BF (BF) slag and observe the CaO-SiO2-MgO-Al2O3-TiO2 5-element slag system with the binary basicity fixed at 1.17. The specific heat capacity of the BF slag and the cooling heat distribution were obtained during the cooling process when the MgO content changing from 7% to 11%. The results showed that the heat released of BF slag was more than 1.2 GJ/ton during the cooling process from 1400 °C to 35 °C, of which the sensible heat was dominant. At MgO content of 9%, the latent heat of crystallization is maximum. The cooling and heat release law of BF slag is directly associated with the phase precipitated in slag cooling and micromorphology.

Cardiac contractility and sarcolemmal calcium binding in several cardiac muscle preparations

1981 ◽  
Vol 240 (4) ◽  
pp. H576-H583 ◽  
Author(s):  
D. M. Bers ◽  
K. D. Philipson ◽  
G. A. Langer
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Calcium Binding ◽  
Cardiac Contractility ◽  
Neonatal Rat ◽  
Cardiac Sarcolemma ◽  
Tension Development ◽  
Adult Rat ◽  
Ventricular Tissue ◽  
Rat Ventricle ◽  
Rabbit Atrium

Striking correlations are found between cardiac contractility and Ca2+ binding to isolated cardiac sarcolemma in rabbit, neonatal rat, and frog ventricular tissue. Deviations from this correlation are seen in the adult rat ventricle and rabbit atrium. The observation of this correlation in the three former tissues and under various ionic conditions suggests that this correlation is not coincidental and that Ca2+ bound to the cardiac sarcolemma is of major importance in the control of myocardial contractility. The data are consistent with a functional Ca2+-induced Ca2+ release system in the sarcoplasmic reticulum (SR) of all the tissues (which is controlled by Ca2+ entry from sarcolemmal sites), with the adult rat ventricular and rabbit atrial SR Ca2+ release being much more sensitive to CA2+. It is suggested that the frog, neonatal rat, and rabbit ventricles depend more directly on the entry of Ca2+ from sarcolemmal sites for the control of tension development, whereas the adult rat ventricle and rabbit atrium depend to a greater extent on CA2+ released from the SR.

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