Tension-dependent and tension-independent energy components of heart contraction

Abstract

Heat production and isovolumetric pressure development (P) were measured simultaneously in the arterially perfused rat ventricle. The time course of the calorimetric signal that follows a contraction could be decomposed into four components of energy released. Three of these components (H1, H2, and H4) were pressure independent, only H3 correlated with either P or the pressure-time integral (PtI) (r > 0.78, n = 36, P < 0.01). The dimensionless slope of the regression of H3 on P was 0.24 (an index of muscle economy) and the absence of O2 (N2 replacement) decreased it to 0.178 suggesting that 26% of H3 is related to oxidative metabolism. H4 was the most affected by the lack of O2 in the perfusate. It decreased to 16% in the first beat under N2 without change in P or in H1, H2 or H3, and disappeared (1.6 +/- 1.0 mJ.g-1) in the fourth contraction under N2 (while P, H1, H2 and H3 remained over 64% of their control values). H4 was activated during the first 1-3 beats after a quiescent period and remained active for several seconds (even in the absence of subsequent stimulation) as if the basal metabolism had been increased to a new steady level. H1 and H2 were dependent on the extracellular Ca. The magnitudes of both H1 (1.8 +/- 0.2 mJ.g-1) and H2 (2.7 +/- 0.2 mJ.g-1) were similar to those reported for the fast and slow components of activation heat in skeletal muscle. If twin stimuli are applied (200 ms apart), additional energy is released (+3.0 +/- 0.3 mJ.g-1) that can be decomposed in two components similar to those identified as H2 and H3. The magnitude of H1, its absence in the twin contraction and its Ca dependency suggest an association with Ca-binding processes (mainly Troponin C). The presence of an H2 component during the twin contraction, its magnitude and Ca dependence gives support to a relationship between H2 and Ca removal processes.

CARDIAC Role of the Mitochondrial Ca2+ Transporters in the High-[K+]o Cardioprotection of Rat Hearts Under Ischemia and Reperfusion: A Mechano-Energetic Study

“…It was retrogradely perfused with Krebs solution by Langendorff technique, at a constant flow of 6 mL/min per gram kept by a peristaltic pump (Gilson Minipuls, France). 16,17,19,20 Both atria were removed and a little cut was done on the interventricular septum to eliminate the spontaneous beating. A latex balloon was introduced in the left ventricle and connected by a flexible cannula to a Bentley DEL900 pressure transducer.…”

“…It was similar to that used in previous works. 16,17,19 Sodium 5-hydroxidecanoate (5HD, ICN Biochemicals and Reagents, CA) was prepared as a 100 mmol/L solution in DMSO and diluted to 100 mmol/L in CPG. Clonazepam (Clzp, Saporiti, Argentina) was prepared as an aqueous solution at 10 mM and diluted to either 10 or 30 mmol/L in CPG for perfusion.…”

“…When it is beating, the total heat release includes the active heat rate (Ht-Hr), which contains the tension-dependent and tension-independent fractions, associated respectively with the myofilaments and Ca 2+ -removal ATP hydrolysis and resynthesis. [17][18][19][20][21] The aim of this work was to mechano-energetically evaluate the effect of drugs acting on the mitochondrial transporters (mK ATP channels, Ca 2+ -U, mNCX, and mPTP) during the high-K + -low Ca 2+ -CPG pretreatment on isolated rat hearts exposed to no-flow I/R to understand the role of mitochondria in cardioprotection.…”

Effects of pyruvate on the energetics of rat ventricles stunned by ischemia–reperfusion

“…The aim of this work was to evaluate whether Pyr and CPG are additive as cardioprotectives in the stunned heart, and the energetic consequences on post-ischemic hearts. Online calorimetry was employed, since it was extensively used for studying the energetics of Ca 2+ movements in resting and beating hearts (Ponce-Hornos et al 1982, 1995Bonazzola and Takara 2010), as well as under ischemia and hypoperfusion (Consolini et al 2001(Consolini et al , 2007Ragone et al 2013). The myothermic analysis in ventricles was complemented with measurements of mitochondrial and cytosolic [Ca 2+ ] in ventricular cardiomyocytes to suggest the underlying mechanisms of Pyr, either added to a cold cardioplegia or as a unique pretreatment in a model of cardiac stunning.…”

Predictability of O2 Consumption from Contractility and Mechanical Energy of Absolute Arrhythmic Beats in Canine Heart

“…1 in individual arrhythmic beats, since the time resolution of VO 2 measurement as coronary flow times coronary arteriovenous O 2 content difference is not short enough to detect its beat-by-beat changes. In contrast, the heat measurement seems to have a reasonably high time resolution, which is enough to measure the beat-bybeat changes in myocardial or cardiac energetics [20,21]. Therefore, the present proposed formula remains to be validated on a per-beat basis by the myothermal method.…”