Cytosolic Ca2+ concentration during Ca2+ depletion of isolated rat hearts

Myosin heavy chain and cardiac troponin T damage is associated with impaired myofibrillar ATPase activity contributing to sarcomeric dysfunction in Ca2+-paradox rat hearts

This study aimed to explore the potential contribution of myofibrils to contractile dysfunction in Ca2+-paradox hearts. Isolated rat hearts were perfused with Krebs-Henseleit solution (Control), followed by Ca2+-depletion, and then Ca2+-repletion after Ca2+-depletion (Ca2+-paradox) by Langendorff method. During heart perfusion left ventricular developed pressure (LVDP), end-diastolic pressure (LVEDP), rate of pressure development (+ dP/dt), and pressure decay (-dP/dt) were registered. Control LVDP (127.4 ± 6.1 mmHg) was reduced during Ca2+-depletion (9.8 ± 1.3 mmHg) and Ca2+-paradox (12.9 ± 1.3 mmHg) with similar decline in +dP/dt and -dP/dt. LVEDP was increased in both Ca2+-depletion and Ca2+-paradox. Compared to Control, myofibrillar Ca2+-stimulated ATPase activity was decreased in the Ca2+-depletion group (12.08 ± 0.57 vs. 8.13 ± 0.19 µmol Pi/mg protein/h), besides unvarying Mg2+ ATPase activity, while upon Ca2+-paradox myofibrillar Ca2+-stimulated ATPase activity was decreased (12.08 ± 0.57 vs. 8.40 ± 0.22 µmol Pi/mg protein/h), but Mg2+ ATPase activity was increased (3.20 ± 0.25 vs. 7.21 ± 0.36 µmol Pi/mg protein/h). In force measurements of isolated cardiomyocytes at saturating [Ca2+], Ca2+-depleted cells had lower rate constant of force redevelopment (k tr,max, 3.85 ± 0.21) and unchanged active tension, while those in Ca2+-paradox produced lower active tension (12.12 ± 3.19 kN/m2) and k tr,max (3.21 ± 23) than cells of Control group (25.07 ± 3.51 and 4.61 ± 22 kN/m2, respectively). In biochemical assays, α-myosin heavy chain and cardiac troponin T presented progressive degradation during Ca2+-depletion and Ca2+-paradox. Our results suggest that contractile impairment in Ca2+-paradox partially resides in deranged sarcomeric function and compromised myofibrillar ATPase activity as a result of myofilament protein degradation, such as α-myosin heavy chain and cardiac troponin T. Impaired relaxation seen in Ca2+-paradoxical hearts is apparently not related to titin, rather explained by the altered myofibrillar ATPase activity.

Cardiac basal metabolism: energetic cost of calcium withdrawal in the adult rat heart

AIM

Cardiac basal metabolism upon extracellular calcium removal and its relationship with intracellular sodium and calcium homeostasis was evaluated.

METHODS

A mechano-calorimetric technique was used that allowed the simultaneous and continuous measurement of both heat rate and resting pressure in arterially perfused quiescent adult rat hearts. Using pharmacological tools, the possible underlying mechanisms related to sodium and calcium movements were investigated.

RESULTS

Resting heat rate (expressed in mW g(-1)(dry wt)) increased upon calcium withdrawal (+4.4 +/- 0.2). This response was: (1) unaffected by the presence of tetrodotoxin (+4.3 +/- 0.6), (2) fully blocked by both, the decrease in extracellular sodium concentration and the increase in extracellular magnesium concentration, (3) partially blocked by the presence of either nifedipine (+2.8 +/- 0.4), KB-R7943 (KBR; +2.5 +/- 0.2), clonazepam (CLO; +3.1 +/- 0.3) or EGTA (+1.9 +/- 0.3). The steady heat rate under Ca(2+)-free conditions was partially reduced by the addition of Ru360 (-1.1 +/- 0.2) but not CLO in the presence of EGTA, KBR or Ru360.

CONCLUSION

Energy expenditure for resting state maintenance upon calcium withdrawal depends on the intracellular rise in both sodium and calcium. Our data are consistent with a mitochondrial Ca(2+) cycling, not detectable under normal calcium diastolic levels. The experimental condition here analysed, partially simulates findings reported under certain pathological situations including heart failure in which mildly increased levels of both diastolic sodium and calcium have also been found. Therefore, under such pathological conditions, hearts should distract chemical energy to fuel processes associated with sodium and calcium handling, making more expensive the maintenance of their functions.

Identification of a switching model of calcium cycling in isolated rat hearts

So far, the processes involved in regulation of intracellular calcium (Ca/sub i//sup 2+/) in cardiomyocytes have been mainly studied through biochemical and isolated cell analysis. Here, we present a novel technique to model and identify cardiac Ca/sub i//sup 2+/-cycling under physiologically relevant conditions in the intact beating heart. Ca/sub i//sup 2+/ was measured using fluorescence techniques in ex vivo perfused rat hearts. For analysis, we developed a parametric mathematical model, switching between active and inactive calcium release. The kinetic parameters of the two submodes of the model were computed using a recently developed technique from hybrid system identification. Application of the method to control and isoproterenol-stimulated hearts resulted in parameter values within a physiologically reliable range.

β-Adrenergic activation reveals impaired cardiac calcium handling at early stage of diabetes

Cardiac function is known to be impaired in diabetes. Alterations in intracellular calcium handling have been suggested to play a pivotal role. This study aimed to test the hypothesis that beta-adrenergic activation can reveal the functional derangements of intracellular calcium handling of the 4-week diabetic heart. Langendorff perfused hearts of 4-week streptozotocin-induced diabetic rats were subjected to the beta-adrenoceptor agonist isoproterenol. Cyclic changes in [Ca(2+)](i) levels were measured throughout the cardiac cycle using Indo-1 fluorescent dye. Based on the computational analysis of the [Ca(2+)](i) transient the kinetic parameters of the sarcoplasmic reticulum Ca(2+)-ATPase and the ryanodine receptor were determined by minimizing the squared error between the simulated and the experimentally obtained [Ca(2+)](i) transient. Under unchallenged conditions, hemodynamic parameters were comparable between control and diabetic hearts. Isoproterenol administration stimulated hemodynamic function to a greater extent in control than in diabetic hearts, which was exemplified by more pronounced increases in rate of pressure development and decline. Under unchallenged conditions, [Ca(2+)](i) amplitude and rate of rise and decline of [Ca(2+)](i) as measured throughout the cardiac cycle were comparable between diabetic and control hearts. Differences became apparent under beta-adrenoceptor stimulation. Upon beta-activation the rate-pressure product showed a blunted response, which was accompanied by a diminished rise in [Ca(2+)](i) amplitude in diabetic hearts. Computational analysis revealed a reduced function of the sarcoplasmic reticulum Ca(2+)-ATPase and Ca(2+)-release channel in response to beta-adrenoceptor challenge. Alterations in Ca(2+)(i) handling may play a causative role in depressed hemodynamic performance of the challenged heart at an early stage of diabetes.

Activation of polymorphonuclear neutrophils by immune complex: possible involvement in development of transfusion-related acute lung injury

Transfusion-related acute lung injury (TRALI) is a serious side-effect of transfusion. We presumed that immune complex (IC)-activated polymorphonuclear neutrophils (PMNs) are involved in the development of TRALI. The aim of this study is to examine the various effects of ICs on normal human PMNs. ICs used here were artificially formed by combining soluble human leucocyte antigen (HLA) class II-positive serum and anti-HLA class II antiserum. The abilities of ICs to trigger PMNs and induce the production of soluble mediators and the involvement of the Fc receptor (FcR) in the activation of PMNs by ICs were investigated. Moreover, the ability of the culture supernatant of PMNs incubated with ICs regarded to induce the apoptosis of lung microvascular endothelial (LME) cells was examined. The results proved that PMNs are triggered by ICs resulting in the acceleration of the production of tumour necrosis factor-alpha (TNF-alpha), perforin and Fas ligand, in which FcR on PMNs appears to be involved. Furthermore, the culture supernatants of PMNs cultured with ICs were revealed to induce the apoptosis of LME cells. In conclusion, the ICs used here were proved to induce PMNs to release cytotoxic factors upon activation. These results suggest that ICs are mediators of the development of TRALI.