Miroslav Ferko

Mitochondrial membrane fluidity, potential, and calcium transients in the myocardium from acute diabetic rats

In this study, we report for the first time concurrent measurements of membrane potential and dynamics and respiratory chain activities in rat heart mitochondria, as well as calcium transients in the hearts of rats in an early phase of streptozotocin diabetes, not yet accompanied with diabetes-induced complications. Quantitative relationships among these variables were assessed. The mitochondria from diabetic rats exhibited decreased fluorescence anisotropy values of diphenylhexatriene. This indicates that hydrophobic core of the membranes was more fluid compared with controls (p<0.05). We discuss the changes in fluidity as having been associated with augmented energy transduction through the diabetic membranes. Reduced ratio of JC-1 fluorescence (aggregates to monomers) in the mitochondria from diabetic hearts reflected descendent transmembrane potential. A significant negative association between membrane fluidity and potential in the diabetic group was found (p<0.05; r=0.67). Further, we observed an increase in calcium transient amplitude (CTA) in the diabetic cardiomyocytes (p=0.048). We conclude that some of the calcium-induced regulatory events that dictate fuel selection and capacity for ATP production in diabetic heart occur at the membrane level. Our findings offer new insight into acute diabetes-induced changes in cardiac mitochondria.

Calcium signaling-mediated endogenous protection of cell energetics in the acutely diabetic myocardium.

In acute diabetic myocardium, calcium signals propagated by intracellular calcium transients participate in the protection of cell energetics via upregulating the formation of mitochondrial energy transition pores (ETP). Mechanisms coupling ETP formation with an increase in membrane fluidity and a decrease in transmembrane potential of the mitochondria are discussed. Our results indicate that the amplification of calcium transients in the diabetic heart is associated with an increase in their amplitude. Moreover, the signals transferred by calcium transients also regulated ETP formation in nondiabetic myocardium. Evidence for the indispensable role of calcium in the regulation of transition pore formation is provided whereby an exchange of cadmium for calcium ions led to a rapid and dramatic decrease in the amount of ETP. Another possible regulatory factor of the mitochondrial function may be radical-induced damage to the diabetic heart. Nevertheless, our data indicate that radical-induced changes in mitochondria predominantly concern the respiratory chain and have no appreciable effect on the fluidity of the mitochondrial membranes. The residual mitochondrial production of ATP owing to its augmented transfer to the cytosol proved to be adequate to preserve sufficient levels of adenine nucleotides in the acute diabetic myocardium.

Impact of age and sex on response to ischemic preconditioning in the rat heart: differential role of the PI3K-AKT pathway.

Sex and aging represent important factors that determine morbidity and mortality due to cardiovascular diseases in the human population. This study aimed to investigate the impact of aging on the response to ischemia-reperfusion in male and female rat hearts, and to explore a potential role of the PI3K-Akt pathway in the cardioprotective effects of ischemic preconditioning (IPC) in the myocardium of younger and older adult males and females. Langendorff-perfused nonpreconditioned and preconditioned hearts of 12- and 18-week-old male and female Wistar rats were subjected to regional ischemia and reperfusion with or without prior perfusion with the PI3K inhibitor wortmannin for the evaluation of ischemia-induced arrhythmias and the size of myocardial infarction (infarct size; IS). Aging did not modify IS in both sexes; however, it markedly increased susceptibility to arrhythmias. Although IPC effectively reduced IS in males and females of both ages, only the hearts of males and 18-week-old females benefited from its antiarrhythmic effect. In the preconditioned 12-week-old females, but not the 18-week-old females, and in males of both ages, wortmannin blunted the anti-infarct effect of IPC. In conclusion, activation of the PI3K-Akt pathway plays an important role in protection against lethal injury conferred by IPC in males irrespective of age. The IS-limiting effect of IPC appears to be PI3K-Akt-dependent only in the 12-week-old females.

Pleiotropic preconditioning-like cardioprotective effects of hypolipidemic drugs in acute ischemia-reperfusion in normal and hypertensive rats.

Although pleiotropy, which is defined as multiple effects derived from a single gene, was recognized many years ago, and considerable progress has since been achieved in this field, it is not very clear how much this feature of a drug is clinically relevant. During the last decade, beneficial pleiotropic effects from hypolipidemic drugs (as in, effects that are different from the primary ones) have been associated with reduction of cardiovascular risk. As with statins, the agonists of peroxisome proliferator-activated receptors (PPARs), niacin and fibrates, have been suggested to exhibit pleiotropic activity that could significantly modify the outcome of a cardiovascular ailment. This review examines findings demonstrating the impacts of treatment with hypolipidemic drugs on cardiac response to ischemia in a setting of acute ischemia-reperfusion, in relation to PPAR activation. Specifically, it addresses the issue of susceptibility to ischemia, with particular regard to the preconditioning-like cardioprotection conferred by hypolipidemic drugs, as well as the potential molecular mechanisms behind this cardioprotection. Finally, the involvement of PPAR activation in the mechanisms of non-metabolic cardioprotective effects from hypolipidemic drugs, and their effects on normal and pathologically altered myocardium (in the hearts of hypertensive rats) is also discussed.

Dual influence of spontaneous hypertension on membrane properties and ATP production in heart and kidney mitochondria in rat: effect of captopril and nifedipine, adaptation and dysadaptation

This study deals with changes, induced by hypertension and its treatment, in the function and properties of mitochondria in the heart and kidneys. Male, 16-week-old hypertensive rats were allocated to 3 groups: (i) animals treated daily for 4 weeks with captopril (CAP, 80 mg·(kg body mass)(-1), n = 45), (ii) animals treated with CAP + nifedipine (NIF, 10 mg·kg(-1), n = 45), or (iii) untreated hypertensive controls (n = 96). Wistar rats (n = 96) were used as normotensive controls. Systolic blood pressure (SBP), heart rate (HR), and heart mass / body mass (HW/BW) ratio were measured at the beginning and end of the experiments; measurements for mitochondrial Mg(2+)-ATPase activity, O(2)-consumption (QO(2)), respiratory control index (RCI), ADP/O, oxidative phosphorylation rate (OPR), conjugated diene content (CD), and membrane fluidity (MF) were also taken at different time intervals. In the heart, elevated SBP, HR, and HW/BW accompanied increased QO(2), OPR, and Mg(2+)-ATPase activity, indicating an adaptive response to hypertension-induced increase in the energy demands of the myocardium. Treatments with CAP or with CAP + NIF were very similar in their prevention of increase in SBP, HR, HW/BW, and the rise in OPR (all p < 0.05-0.01). In the kidneys, hypertension induced a drop in OPR; however, antihypertensive therapy aggravated the resulting energy deficiency, whereby treatment with CAP + NIF was more detrimental than treatment with CAP alone. Heart and kidney mitochondria exhibited negligible changes in CD and moderately increased MF, which was more potentiated by treatment with CAP alone than with CAP + NIF.

Mitochondria as a target of cardioprotection in models of preconditioning

Over the recent years the view on mitochondria in the heart as a cellular powerhouse providing ATP supply needed to sustain contractile function, basal metabolic processes, and ionic homeostasis has changed radically. At present it is known that dysfunctions of these organelles are essential in the development of a large number of diseases, including cardiovascular diseases. Moreover, mitochondria are considered to be a very promising target of endogenous strategies that are essential in the protection of the myocardium from acute ischemia/reperfusion injury. These strategies including ischemic preconditioning, remote ischemic preconditioning as well as the acute phase of streptozotocin-induced diabetes mellitus, provide a similar effect of protection. Alterations observed in the functional and structural properties of heart mitochondria caused by short-term pathological impulses are associated with endogenous cardioprotective processes. It seems that the extent of mitochondrial membrane fluidization could be an active response mechanism to injury with a subtle effect on membrane-associated processes which further affect the environment of the whole organelle, thus inducing metabolic changes in the heart. In this review article, we provide an overview of endogenous protective mechanisms induced by hypoxic, pseudohypoxic and ischemic conditions with special consideration of the role of heart mitochondria in these processes.

Changes in mitochondrial properties may contribute to enhanced resistance to ischemia–reperfusion injury in the diabetic rat heart1

Diabetes mellitus, besides having deleterious effects, induces cardiac adaptation that may reduce the hearts susceptibility to ischemia-reperfusion (IR) injury. This study aimed to investigate whether changes in mitochondrial properties are involved in the mechanisms of increased resistance of the diabetic heart to IR. Adult male Wistar rats were made diabetic by a single dose of streptozotocin (65 mg·kg-1, i.p.), and on the day 8, Langendorff-perfused hearts were subjected to 30 min global ischemia and 40 min reperfusion. Baseline preischemic parameters in the diabetic hearts did not differ markedly from those in the nondiabetic controls, except for lower left ventricular developed pressure, higher mitochondrial membrane fluidity, and protein levels of manganese superoxide dismutase. On the other hand, diabetic hearts showed significantly better post-IR functional restoration and reduced arrhythmogenesis associated with lower reactive oxygen species production as compared with healthy controls. IR decreased membrane fluidity in both experimental groups; however, it led to a complete recovery of mitochondrial Mg2+-ATPase activity in diabetics in contrast to its reduction in nondiabetics. These findings indicate that the heart may become adapted to diabetes-induced alterations that might increase its tolerance to an ischemic insult. Preserved mitochondrial function might play a role in the mechanisms of the hearts resistance to IR injury in diabetics.