Rationale In cardiomyocytes from failing hearts, insufficient mitochondrial Ca2+ ([Ca2+]m) accumulation secondary to cytoplasmic Na+ overload decreases NAD(P)H/NAD(P)+ redox potential and increases oxidative stress when workload increases. These effects are abolished by enhancing [Ca2+]m with acute treatment with CGP-37157 (CGP), an inhibitor of the mitochondrial Na+/Ca2+ exchanger. Objective To determine if chronic CGP treatment mitigates contractile dysfunction and arrhythmias in an animal model of heart failure (HF) and sudden cardiac death (SCD). Methods and Results Here, we describe a novel guinea-pig HF/SCD model employing aortic constriction combined with daily β-adrenergic receptor stimulation (ACi) and show that chronic CGP treatment (ACi+CGP) attenuates cardiac hypertrophic remodeling, pulmonary edema, and interstitial fibrosis and prevents cardiac dysfunction and SCD. In the ACi group 4 weeks after pressure-overload, fractional shortening and the rate of left ventricular pressure development decreased by 36% and 32%, respectively, compared to sham-operated controls; in contrast, cardiac function was completely preserved in the ACi+CGP group. CGP treatment also significantly reduced the incidence of premature ventricular beats and prevented fatal episodes of ventricular fibrillation, but did not prevent QT prolongation. Without CGP treatment, mortality was 61% in the ACi group within 4 weeks of aortic constriction, while the death rate in the ACi+CGP group was not different from sham-operated animals. Conclusions The findings demonstrate the critical role played by altered mitochondrial Ca2+ dynamics in the development of HF and HF-associated SCD; moreover, they reveal a novel strategy for treating SCD and cardiac decompensation in HF.

Transient Ca(2+)/polyP-mediated mPTP opening during ischaemia may serve to protect cells against cytosolic Ca(2+) overload, whereas ROS/pH-mediated sustained mPTP opening on reperfusion induces cell death.

Rationale Mitochondrial [Ca2+] ([Ca2+]mito) regulates mitochondrial energy production, provides transient Ca2+buffering under stress and can be involved in cell death. Mitochondria are near the sarcoplasmic reticulum (SR) in cardiac myocytes and evidence for crosstalk exists. However, quantitative measurements of [Ca2+]mito are limited and spatial [Ca2+]mito gradients have not been directly measured. Objective To directly measure local [Ca2+]mito during normal SR Ca release in intact myocytes, and evaluate potential subsarcomeric spatial [Ca2+]mito gradients. Methods and Results We used in-situ calibration of the mitochondrially targeted inverse pericam indicator Mitycam and directly measured [Ca2+]mito during SR Ca2+ release in intact rabbit ventricular myocytes by confocal microscopy. During steady state pacing Δ[Ca2+]mito amplitude was 29 ± 3 nM, rising rapidly (similar to cytosolic [Ca2+]i) but declining much more slowly. Taking advantage of the structural periodicity of cardiac sarcomeres, we found that [Ca2+]mito near SR Ca2+ release sites (Z-lines) vs. mid sarcomere (M-line) reached a higher peak amplitude (37 ± 4 vs. 26 ± 4 nM, respectively P < 0.05) which occurred earlier in time. This difference was attributed to ends of mitochondria being physically closer to SR Ca2+ release sites, because the mitochondrial Ca2+ uniporter was homogeneously distributed and elevated [Ca2+] applied laterally did not produce longitudinal [Ca2+]mito gradients. Conclusions We developed methods to measure spatiotemporal [Ca2+]mito gradients quantitatively during excitation-contraction coupling. The amplitude and kinetics of [Ca2+]mito transients differ significantly from those in the cytosol and are higher and faster near the Z- vs. M-line. This approach will help clarify SR-mitochondrial Ca2+ signaling.

Aims: Mitochondrial Ca 2+ homeostasis is crucial for balancing cell survival and death. The recent discovery of the molecular identity of the mitochondrial Ca 2+ uniporter pore (MCU) opens new possibilities for applying genetic approaches to study mitochondrial Ca 2+ regulation in various cell types, including cardiac myocytes. Basal tyrosine phosphorylation of MCU was reported from mass spectroscopy of human and mouse tissues, but the signaling pathways that regulate mitochondrial Ca 2+ entry through posttranslational modifications of MCU are completely unknown. Therefore, we investigated a 1 -adrenergic-mediated signal transduction of MCU posttranslational modification and function in cardiac cells. Results: a 1 -adrenoceptor (a 1 -AR) signaling translocated activated proline-rich tyrosine kinase 2 (Pyk2) from the cytosol to mitochondrial matrix and accelerates mitochondrial Ca 2+ uptake via Pyk2-dependent MCU phosphorylation and tetrametric MCU channel pore formation. Moreover, we found that a 1 -AR stimulation increases reactive oxygen species production at mitochondria, mitochondrial permeability transition pore activity, and initiates apoptotic signaling via Pyk2-dependent MCU activation and mitochondrial Ca 2+ overload. Innovation: Our data indicate that inhibition of a 1 -AR-Pyk2-MCU signaling represents a potential novel therapeutic target to limit or prevent mitochondrial Ca 2+ overload, oxidative stress, mitochondrial injury, and myocardial death during pathophysiological conditions, where chronic adrenergic stimulation is present. Conclusion: The a 1 -AR-Pyk2-dependent tyrosine phosphorylation of the MCU regulates mitochondrial Ca 2+ entry and apoptosis in cardiac cells. Antioxid. Redox Signal. 21, 863-879.

No abstract