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In the present work, the effect of isoproterenol on the electrical properties of the rat heart and on the cytoarchitecture of the surviving cardiomyocytes was studied. Myocardial remodelling was induced by the daily administration of 5 mg/kg isoproterenol (Iso) for 7 days. Administration resulted in a significant increase (52%) in the ratio of left ventricular weight to body weight. ECG voltage criteria confirmed the presence of left ventricular hypertrophy. QT interval prolongation by 23% and 58% was found in Iso rats and in the corresponding isolated hearts, respectively. Spontaneously beating Iso hearts had a higher incidence of dysrhythmias. The surviving cardiomyocytes showed an irregular shape with cytoplasmic processes rich in ribosomes and rough endoplasmic reticulum. In these regions, myofibril disorganization and mitochondrial fission were observed. A greatly increased incidence of caveolae was seen in the plasma membrane and in the mouth of t-tubules. The membranes of t-tubules showed vesiculation, especially near the dyads. Repeated administration of isoproterenol led to hypertrophy, characterized by the existence of myocytes with simultaneous signs of both mature and postnatally developing cardiomyocytes. Structural microheterogeneities at the level of individual cells may represent one of the factors leading to electrical imbalance in the myocardial tissue remodelled by isoproterenol. Key words: heart, isoproterenol, hypertrophy, ECG, contractile dysfunction, ultrastructure, plasma membrane, mitochondria, t-tubules. Dans le present travail, on a examine l'effet de l'isoproterenol sur les proprieteeselectriques du coeur de rat et sur la cytoarchitecture des cardiomyocytes survivants. Le remodelage myocardique a ete induit par l'administration quotidienne de 5 mg/kg d'isoproterenol (Iso) durant 7 jours. L'administration de l'Iso a cause; une augmentation significative (de 52 %) du rapport poids ventriculaire gauche a poids corporel. Les criteres de voltage ECG ont confirme la presence de l'hypertrophie ventriculaire gauche. De plus, une prolongation de l'intervalle QT de 23 et 58 % s'est produite chez les rats ayant recju l'Iso et dans les coeurs isoles correspondants, respectivement. Les Iso-coeurs a battements spontanees ont eu une plus forte incidence de dysrythmies. Les cardiomyocytes survivants avaient une forme irreguliere ainsi qu'un cytoplasme riche en ribosomes et en reticulum endoplasmique granulaire. Dans ces regions, une desorganisation myofibrillaire et une fission mitochondriale ont ete observeees. De tres grandes quantitees de caveeoles ont ete releveees dans la membrane plasmatique et a l'entree des tubules T. Les membranes des tubules T ont montre une vesiculation, en particulier pres des dyades. L'administration repetee d'isoproterenol a entraine une hypertrophie caracteerisee par la presence de myocytes montrant des signes de cardiomyocytes tant developpesa la naissance que matures. Les microheeterogeneeites structurales au niveau des cellules individuelles pourraient representer l'un des facteurs menant a un deseequilibre electrique dans le tissu myocardique remodele par l'isoproterenol. Mots-cles: coeur, isoproterenol, hypertrophie, ECG, dysfonction contractile, ultrastructure, membrane plasmatique, mitochondries, tubules T. [Traduit par la Redaction], Introduction Left ventricular hypertrophy is an independent adaptive response to hemodynamic overload (Wang et al. 2003; Diwan and Dorn 2007) and a risk factor for sudden cardiac death. Experimental myocardial [...]

Understanding muscle adaptation to various stimuli is difficult because of the complex nature of stimuli and responses. In particular, responses to perturbations in energy metabolism require careful examination, because they may involve both structural and functional elements. To estimate the structural component of the myocyte adaptation to energetic deficiency, we used transgenic mice with blocked expression of mitochondrial and cytosolic creatine kinases (CK). The ultrastructure was analyzed using the stereological method of vertical sections applied to electron microscopic images of ultrathin longitudinal sections of fast muscle fibers of gastrocnemius, known to adapt to CK deficiency by increasing oxidative metabolism. The lack of CK induced a profound structural adaptation response that included changes in the volume and surface densities of major organelles. In addition, using a new stereological parameter, the environment of an organelle, substantial changes in the mitochondrial neighborhood were identified pointing to their relocation closer to the major sites of energy consumption, supposedly to compensate for invalidated energy transfer. Using quantitative arguments, we have shown for the first time that spatial relations among organelles of muscle cells undergo adaptation in response to nonstructural stimuli like metabolic deficiency. skeletal muscle cells; structure; adaptation; energy deficiency

Aims Endoplasmic reticulum (ER) stress has recently emerged as an important mechanism involved in the pathogenesis of cardiovascular diseases. However, the molecular mechanisms by which ER stress leads to cardiac dysfunction remain poorly understood. Methods and results In this study, we evaluated the early cardiac effects of ER stress induced by tunicamycin (TN) in mice. Echocardiographic analysis indicated that TN-induced ER stress led to a significant impairment of the cardiac function. Electron microscopic observations revealed that ultrastructural changes of cardiomyocytes in response to ER stress manifested extensively at the level of the reticular membrane system. Smooth tubules of sarcoplasmic reticulum in connection with short sections of rough ER were observed. The presence of rough instead of smooth reticulum was increased at the interfibrillar space, at the level of dyads, and in the vicinity of mitochondria. At the transcriptional level, ER stress resulted in a substantial decrease in the expression of the major regulator of mitochondrial biogenesis PGC-1α and of its targets NRF1, Tfam, CS, and COXIV. At the functional level, ER stress also induced an impairment of mitochondrial Ca2+ uptake, an alteration of mitochondrial oxidative phosphorylation, and a metabolic remodelling characterized by a shift from fatty acid to glycolytic substrate consumption. Conclusions Our findings show that ER stress induces cytoarchitectural and metabolic alterations in cardiomyocytes and provide evidences that ER stress could represent a primary mechanism that contributes to the impairment of energy metabolism reported in most cardiac diseases. [ABSTRACT FROM AUTHOR]

Stress is one of the major contributors to the development of cardiovascular disorders and psychiatric illnesses. Immobilization stress belongs to severe stressors and is known to activate several calcium transport systems. The aim of this work was to determine whether repeated immobilization stress changes mRNA and protein levels of the type 1 and 2 inositol-1,4,5-trisphosphate (IP3 ) receptors in cardiac tissue. Rats were immobilized for 7 days, 2 h daily. After repeated immobilization, increased numbers of collagen fibers were accumulated in the heart atria compared to hearts of the control group of rats. Gene expression was determined after reverse transcription and subsequent real-time polymerase chain reaction, using SYBR Green fluorescent dye. Protein levels were determined by Western blot and hybridization with the primary antibody against IP3 receptors. Contrary to single immobilization, repeated immobilization decreased a gene expression of the type 1 and 2 IP3 receptors, and also protein levels of the IP3 receptors. Although the physiologic relevance of our observations remains to be elucidated, we propose that the decrease in IP3 receptors may have an impact on the development of the pathophysiologic changes in the heart. [ABSTRACT FROM AUTHOR]

Phototoxicity is a side-effect of in vitro and in vivo oxygen partial pressure (pO2) detection by luminescence lifetime measurement methods. Dichlorotris(1,10-phenanthroline)-ruthenium(ii) hydrate ([Ru(Phen)3]2+) is a water soluble pO2 probe associated with low phototoxicity, which we investigated in vivo in the chick's chorioallantoic membrane (CAM) after intravenous or topical administration and in vitro in normal human coronary artery endothelial cells (HCAEC). In vivo, the level of intravenously injected [Ru(Phen)3]2+ decreases within several minutes, whereas the maximum of its biodistribution is observed during the first 2 h after topical application. Both routes are followed by convergence to almost identical "intra/extra-vascular" levels of [Ru(Phen)3]2+. In vitro, we observed that [Ru(Phen)3]2+ enters cells via endocytosis and is then redistributed. None of the studied conditions induced modification of lysosomal or mitochondrial membranes without illumination. No nuclear accumulation was observed. Without illumination [Ru(Phen)3]2+ induces changes in endoplasmic reticulum (ER)-to-Golgi transport. The phototoxic effect of [Ru(Phen)3]2+ leads to more marked ultrastructural changes than administration of [Ru(Phen)3]2+ only (in the dark). These could lead to disruption of Ca2+ homeostasis accompanied by mitochondrial changes or to changes in secretory pathways. In conclusion, we have demonstrated that the intravenous injection of [Ru(Phen)3]2+ into the CAM model mostly leads to extracellular localization of [Ru(Phen)3]2+, while its topical application induces intracellular localization. We have shown in vivo that [Ru(Phen)3]2+ induces minimal photo-damage after illumination with light doses larger by two orders of magnitude than those used for pO2 measurements. This low phototoxicity is due to the fact that [Ru(Phen)3]2+ enters endothelial cells via endocytosis and is then redistributed towards peroxisomes and other endosomal and secretory vesicles before it is eliminated via exocytosis. Cellular response to [Ru(Phen)3]2+, survival or death, depends on its intracellular concentration and oxidation-reduction properties.

AMP-activated protein kinase (AMPK) plays an important role in controlling energy homeostasis and is envisioned as a promising target to treat metabolic disorders. In the heart, AMPK is involved in short-term regulation and in transcriptional control of proteins involved in energy metabolism. Here, we investigated whether deletion of AMPKalpha2, the main cardiac catalytic isoform, alters mitochondrial function and biogenesis. Body weight, heart weight, and AMPKalpha1 expression were similar in control littermate and AMPKalpha2(-/-) mice. Despite normal oxygen consumption in perfused hearts, maximal oxidative capacity, measured using saponin permeabilized cardiac fibers, was approximately 30% lower in AMPKalpha2(-/-) mice with octanoate, pyruvate, or glutamate plus malate but not with succinate as substrates, showing an impairment at complex I of the respiratory chain. This effect was associated with a 25% decrease in mitochondrial cardiolipin content, the main mitochondrial membrane phospholipid that is crucial for complex I activity, and with a 13% decrease in mitochondrial content of linoleic acid, the main fatty acid of cardiolipins. The decrease in cardiolipin content could be explained by mRNA downregulation of rate-limiting enzymes of both cardiolipin synthesis (CTP:PA cytidylyltransferase) and remodeling (acyl-CoA:lysocardiolipin acyltransferase 1). These data reveal a new role for AMPKalpha2 subunit in the regulation of cardiac muscle oxidative capacity via cardiolipin homeostasis.

Objective: The aim of the present study was to characterise and compare alterations in the ultrastructure of the functionally identified isolated twitch skeletal muscle fibres of the frog after repeated tetanic stimulation and under experimental conditions which modified their fatigability., Methods: Single isolated twitch muscle fibres of m. iliofibularis of adult frogs Rana temporaria were subjected to intermittent tetanic stimulation. Fibres at specified degree of fatigue were processed for electron microscopic observation and ultrastructural examination., Results: The fatigue-resistant (FR) fibres that developed 90% of the control tetanic tension after 10 min stimulation in ordinary Ringer's solution showed regions with dilated intermyofibrillar spaces containing small vesicles and swollen mitochondria. In addition to the changes observed in FR fibres, the easily fatigued (EF) fibres that produced 50% of the original tension after 3 min stimulation showed small vacuoles in the sarcoplasm. In EF fibres that preserved 10% of the control tension after 10 min stimulation and showed swelling of the longitudinal sarcoplasmic reticulum, the central element of triads and mitochondria, large vacuoles were present. FR fibres exposed to low Ca2+ medium containing 0.02 mmol/l verapamil, lost their resistance to fatigue. Their contractile responses fell down to 20 % within 0.5 min of stimulation. Those fibres displayed large vacuoles and changes in mitochondria as observed in EF fibres after 10 min stimulation., Conclusion: These results suggest that morphological changes accompanying reduction of the contractile force (i) appear earlier than the reduction of the contractile ability, (ii) correlate with the degree of reduction of the contractile capacity but not with the duration of contractile activity, (iii) are not specific for the fatigue fibre type.