[Abstract unavailable

Environmental stresses converge on the mitochondria that can trigger or inhibit cell death. Excitable, postmitotic cells, in response to sublethal noxious stress, engage mechanisms that afford protection from subsequent insults. We show that reoxygenation after prolonged hypoxia reduces the reactive oxygen species (ROS) threshold for the mitochondrial permeability transition (MPT) in cardiomyocytes and that cell survival is steeply negatively correlated with the fraction of depolarized mitochondria. Cell protection that exhibits a memory (preconditioning) results from triggered mitochondrial swelling that causes enhanced substrate oxidation and ROS production, leading to redox activation of PKC, which inhibits glycogen synthase kinase-3β (GSK-3β). Alternatively, receptor tyrosine kinase or certain G protein-coupled receptor activation elicits cell protection (without mitochondrial swelling or durable memory) by inhibiting GSK-3β, via protein kinase B/Akt and mTOR/p70 s6k pathways, PKC pathways, or protein kinase A pathways. The convergence of these pathways via inhibition of GSK-3β on the end effector, the permeability transition pore complex, to limit MPT induction is the general mechanism of cardiomyocyte protection.

Environmental stresses converge on the mitochondria that can trigger or inhibit cell death. Excitable, postmitotic cells, in response to sublethal noxious stress, engage mechanisms that afford protection from subsequent insults. We show that reoxygenation after prolonged hypoxia reduces the reactive oxygen species (ROS) threshold for the mitochondrial permeability transition (MPT) in cardiomyocytes and that cell survival is steeply negatively correlated with the fraction of depolarized mitochondria. Cell protection that exhibits a memory (preconditioning) results from triggered mitochondrial swelling that causes enhanced substrate oxidation and ROS production, leading to redox activation of PKC, which inhibits glycogen synthase kinase-3β (GSK-3β). Alternatively, receptor tyrosine kinase or certain G protein-coupled receptor activation elicits cell protection (without mitochondrial swelling or durable memory) by inhibiting GSK-3β, via protein kinase B/Akt and mTOR/p70 s6k pathways, PKC pathways, or protein kinase A pathways. The convergence of these pathways via inhibition of GSK-3β on the end effector, the permeability transition pore complex, to limit MPT induction is the general mechanism of cardiomyocyte protection.

Stretching of cardiac muscle modulates contraction through the enhancement of the Ca2+ transient, but how this occurs is still not known. We found that stretching of myocytes modulates the elementary Ca2+ release process from ryanodine-receptor Ca2+-release channels (RyRCs), Ca2+ sparks and the electrically stimulated Ca2+ transient. Stretching induces PtdIns-3-OH kinase (PI(3)K)-dependent phosphorylation of both Akt and the endothelial isoform of nitric oxide synthase (NOS), nitric oxide (NO) production, and a proportionate increase in Ca2+-spark frequency that is abolished by inhibiting NOS and PI(3)K. Exogenously generated NO reversibly increases Ca2+-spark frequency without cell stretching. We propose that myocyte NO produced by activation of the PI(3)K-Akt-endothelial NOS axis acts as a second messenger of stretch by enhancing RyRC activity, contributing to myocardial contractile activation.

Background-Regular fish consumption is associated with low cardiovascular disease morbidity and mortality. Fish oils modify cardiac membrane phospholipid fatty acid composition with potent antiarrhythmic effects. We tested the effects of dietary fish oil on ventricular hemodynamics and myocardial oxygen consumption (MVO 2 ). Methods and Results-Male Wistar rats were fed for 16 weeks on a reference diet rich in n-6 polyunsaturated fatty acids (PUFA), a diet rich in saturated animal fat (SAT), or a diet rich in n-3 PUFA from fish oil. Isolated working hearts were perfused with porcine erythrocytes (40% hematocrit) at 75 mm Hg afterload with variable preload (5 to 20 mm Hg) or with low coronary flow ischemia with maintained afterload, preload, and heart rate, then reperfused. MVO 2 was low and coronary perfusion reserve high in n-3 PUFA hearts, and cardiac output increased with workload. The n-3 PUFA reduced ischemic markers-acidosis, K ϩ , lactate, and creatine kinase-and increased contractile recovery during reperfusion. SAT hearts had high MVO 2 , low coronary perfusion reserve, and poor contractile function and recovery. Dietary differences in MVO 2 were abolished by KCl arrest (basal metabolism) or ruthenium red (3.4 mol/L) but not by ryanodine (1 nmol/L). Fish oil or ryanodine, but not ruthenium red, prevented ventricular fibrillation in reperfusion. Conclusions-Dietary fish oil directly influenced heart function and improved cardiac responses to ischemia and reperfusion. The n-3 PUFA reduced oxygen consumption at any given work output and increased postischemic recovery. Thus, direct effects on myocardial function may contribute to the altered cardiovascular disease profile associated with fish consumption.

Aberrations in cell Ca2+ homeostasis have been known to parallel both changes in membrane lipid composition and aging. Previous work has shown that the lowered efficiency of work performance, which occurs in isolated hearts from rats fed a diet rich in n–6 polyunsaturated fatty acids (PUFA), relative to those fed n–3 PUFA, could be raised by mitochondrial (Mito) Ca2+ transport inhibition. We tested whether, after Ca2+-dependent stress, the Ca2+-dependent activation of pyruvate dehydrogenase (PDHA/PDHTotal) and Mito Ca2+ cycling could be manipulated by varying the ratio of n–3 to n–6 PUFA in Mito membranes in young (6 mo) and aged (24 mo) isolated rat hearts treated to n–3 or n–6 PUFA-rich diet. Inotropic stimulation by 1 μM norepinephrine (NE) of 24-mo n–6 PUFA-rich hearts elevated total Mito Ca2+ content 38% more than in 6-mo hearts ( P < 0.05). However, both the NE-induced rise in Mito Ca2+ and the difference in response between 6- and 24-mo hearts were partially abolished by n–3 PUFA treatment. NE increased the fractional activation of PDH by 44% above control levels in the 6-mo group compared with 49% in the 24-mo group after n–6 PUFA diet. However, NE stimulation of PDHA was attenuated by n–3 PUFA diet, attaining values only 29 and 23% above control levels in 6- and 24-mo mitochondria, respectively ( P < 0.05). Global ischemia and reperfusion (I/R) in n–6 PUFA hearts gave rise to higher levels of total Mito Ca2+concentration ( P < 0.0001) and PDHA( P < 0.0001) compared with n–3 PUFA. Ruthenium red (3.4 μM) abolished the effects of I/R in all groups. With aging, heart Mito membrane phosphatidylcholine was increased after n–6 PUFA-rich diet (by ∼15%, P < 0.05), whereas cardiolipin and n–3 PUFA content were diminished by 31% ( P < 0.05) and 73% ( P < 0.05), respectively. These effects were prevented by n–3 PUFA-rich diet. The present study, by directly manipulating the cardiac Mito membrane n–3-to-n–6 PUFA ratio, shows that the activation of Ca2+-dependent PDH can be augmented when the n–3-to-n–6 PUFA ratio is low (n–6 PUFA-rich diet; 24-mo hearts) or attenuated when this ratio is relatively high (n–3 PUFA-rich diet). We propose that one of the consequences of dietary-induced manipulation of membrane phospholipids and PUFAs may be the altered flux of Ca2+ across the Mito membrane and thus altered intramitochondrial Ca2+-dependent processes.

This study demonstrated that oxidative/nitrosylative changes of actin and tropomyosin are largely increased in human failing hearts. Because these changes are inversely correlated to LVEF, actin and tropomyosin oxidation are likely to contribute to the contractile impairment evident in end-stage HF.

We report the development of a novel closed-loop system for cardiac gene therapy. Using this approach delivery of AdS16E reversed HF progression in a large animal HF model.