László Fülöp

Effects of sex hormones on ECG parameters and expression of cardiac ion channels in dogs

Aim:  The aim of the study was to examine the effects of testosterone and oestrogen on the ECG parameters and expression of cardiac ion channels in male and female dogs, and to compare the dofetilide‐induced lengthening of QTc interval in control, castrated and hormone‐treated animals.

When is high-Ca2+ microdomain required for mitochondrial Ca2+ uptake?*

Ca2+ release from IP3‐sensitive stores in the endoplasmic reticulum (ER) induced by Ca2+‐mobilizing agonists generates high‐Ca2+ microdomains between ER vesicles and neighbouring mitochondria. Here we present a model that describes when such microdomains are required and when submicromolar [Ca2+] is sufficient for mitochondrial Ca2+ uptake. Mitochondrial Ca2+ uptake rate in angiotensin II‐stimulated H295R adrenocortical cells correlates with the proximity between ER vesicles and the mitochondrion, reflecting the uptake promoting effect of high‐Ca2+ peri‐mitochondrial microdomains. Silencing or inhibition of p38 mitogen‐activated protein kinase (MAPK) or inhibition of the novel isoforms of protein kinase C enhances mitochondrial Ca2+ uptake and abolishes the positive correlation between Ca2+ uptake and ER‐mitochondrion proximity. Inhibition of protein phosphatases attenuates mitochondrial Ca2+ uptake and also abolishes its positive correlation with ER‐mitochondrion proximity. We postulate that during IP3‐induced Ca2+ release, Ca2+ uptake is confined to ER‐close mitochondria, because of the simultaneous activation of the protein kinases. Attenuation of Ca2+ uptake prevents Ca2+ overload of mitochondria and thus protects the cell against apoptosis. On the other hand, all the mitochondria accumulate Ca2+ at a non‐inhibited rate during physiological Ca2+ influx through the plasma membrane. Membrane potential is higher in ER‐distant mitochondria, providing a bigger driving force for Ca2+ uptake. Our model explains why comparable mitochondrial Ca2+ signals are formed in response to K+ and angiotensin II (equipotent in respect to global cytosolic Ca2+ signals), although only the latter generates high‐Ca2+ microdomains.

The role of mitochondrial Ca2+ and NAD(P)H in the control of aldosterone secretion

The mineralocorticoid hormone aldosterone is synthesized in the zona glomerulosa of the adrenal cortex. Glomerulosa cells respond to the physiological stimuli, elevated extracellular [K(+)] and angiotensin II, with an intracellular Ca(2+) signal. Cytosolic Ca(2+) facilitates the transport of the steroid-precursor cholesterol to mitochondria and, after a few hours, it also induces the transcription of aldosterone synthase. Therefore, the cytosolic Ca(2+) signal is regarded as the most important short and long-term mediator of aldosterone secretion. However, cytosolic Ca(2+) is also taken up by mitochondria and, in turn, the mitochondrial Ca(2+) response activates mitochondrial dehydrogenases resulting in stimulation of respiration and increase in reduced pyridine nucleotides. Since both cholesterol side-chain cleavage and all of the hydroxylation steps of steroid synthesis require NADPH as a cofactor, the importance of cytosolic Ca(2+) - mitochondrial Ca(2+) coupling and of appropriate NADPH supply in respect to hormone production can be assumed. However, the importance of the mitochondrial factors has been neglected so far. Here, after summarizing earlier findings we provide new results obtained through modifying mitochondrial Ca(2+) uptake by knocking down p38 MAPK or OPA1 and overexpressing S100G, supporting the notion that mitochondrial Ca(2+) and reduced pyridine nucleotides are facilitating factors for both basal and stimulated steroid production.

Extramitochondrial OPA1 and adrenocortical function.

We have previously described that silencing of the mitochondrial protein OPA1 enhances mitochondrial Ca(2+) signaling and aldosterone production in H295R adrenocortical cells. Since extramitochondrial OPA1 (emOPA1) was reported to facilitate cAMP-induced lipolysis, we hypothesized that emOPA1, via the enhanced hydrolysis of cholesterol esters, augments aldosterone production in H295R cells. A few OPA1 immunopositive spots were detected in ∼40% of the cells. In cell fractionation studies OPA1/COX IV (mitochondrial marker) ratio in the post-mitochondrial fractions was an order of magnitude higher than that in the mitochondrial fraction. The ratio of long to short OPA1 isoforms was lower in post-mitochondrial than in mitochondrial fractions. Knockdown of OPA1 failed to reduce db-cAMP-induced phosphorylation of hormone-sensitive lipase (HSL), Ca(2+) signaling and aldosterone secretion. In conclusion, OPA1 could be detected in the post-mitochondrial fractions, nevertheless, OPA1 did not interfere with the cAMP - PKA - HSL mediated activation of aldosterone secretion.

Mitochondrial Ca2+ uptake correlates with the severity of the symptoms in autosomal dominant optic atrophy

The most frequent form of hereditary blindness, autosomal dominant optic atrophy (ADOA), is caused by the mutation of the mitochondrial protein Opa1 and the ensuing degeneration of retinal ganglion cells. Previously we found that knockdown of OPA1 enhanced mitochondrial Ca(2+) uptake (Fülöp et al., 2011). Therefore we studied mitochondrial Ca(2+) metabolism in fibroblasts obtained from members of an ADOA family. Gene sequencing revealed heterozygosity for a splice site mutation (c. 984+1G>A) in intron 9 of the OPA1 gene. ADOA cells showed a higher rate of apoptosis than control cells and their mitochondria displayed increased fragmentation when forced to oxidative metabolism. The ophthalmological parameters critical fusion frequency and ganglion cell-inner plexiform layer thickness were inversely correlated to the evoked mitochondrial Ca(2+) signals. The present data indicate that enhanced mitochondrial Ca(2+) uptake is a pathogenetic factor in the progress of ADOA.

Profile of IKs during the action potential questions the therapeutic value of IKs blockade

The goal of this paper is two fold. First, we attempt to review the reports available on the role of I(Ks) in myocardial repolarization. Based on theoretical considerations and experimental results, it seems reasonable to assume that I(Ks)blockade will lengthen the action potential. However, results obtained with I(Ks) blockers, like chromanol 293B or L-735,821, are conflicting, since from slight lengthening to marked prolongation of action potentials were equally obtained. Although these contradictory results were explained by interspecies or regional differences, the role of I(Ks) in repolarization is a matter of growing dispute. In the second part of this study, we simulated the performance of I(Ks) during cardiac action potentials. We compared the profile of the predicted current in three mathematical models in order to determine the relative role of the current in repolarization. We studied the effect of the cycle length, action potential duration and height of the plateau on the profile of I(Ks) in epicardiac, endocardiac and midmyocardiac ventricular action potentials. The results indicate that the height of the plateau is the most important parameter to control activation of I(Ks)in cardiac tissues, and accordingly, the interspecies and regional differences observed in the efficacy of I(Ks) blockers are likely due to the known differences in action potential morphology. We conclude also that I(Ks)blockade may have unpredictable effects on the length of the action potential in a diseased heart, questioning the possible therapeutic value of drugs blocking I(Ks).

Transient Long QT Development in a Patient with Takotsubo Cardiomyopathy

Abstract QT interval prolongation on the electrocardiogram is considered a precursory sign for imminent, potentially lethal ventricular arrhythmias. Beside the inherited condition of long QT syndrome, numerous drugs, certain electrolyte disturbances and early transmural ischemia have been identified to induce reversible prolongation of the QT interval, collectively called as acquired long QT syndrome. Herein we describe a case of a patient with transient QT prolongation and Takotsubo cardiomyopathy, a rather infrequent cause of long QT development. Serial changes of the repolarization pattern were documented to demonstrate progression and resolution of the abnormal QT interval.

Wall motion changes in myocardial infarction in relation to the time elapsed from symptoms until revascularization

Objective Wall motion abnormalities during acute ST-segment elevation myocardial infarction (STEMI) and the improvement after recanalization depend on the conditions of the coronary occlusion. Methods Fifty-seven patients with first-ever STEMI due to one-artery occlusion, treated with primary PCI, were evaluated. Area at risk and left ventricular wall motion abnormalities were localized with coronary angiography and echocardiography and then compared in relation to the time elapsed from the onset of symptoms at the time of infarction and at 3 months. Left ventricular diameters and ejection fractions were evaluated in relation to the ischemic time. Results Three hundred forty-one affected left ventricular segments were detected with angiography, while echocardiography showed 206 segments with motion abnormality. No correlation was found between the regional wall motion index in the area at risk and the time elapsed from the beginning of symptoms. However, the improvement in wall motion abnormalities at the follow-up was dependent on the ischemic time (r=-0.29, p<0.03). The early subgroup showed significant improvement in left ventricular ejection fraction at follow-up (p=0.03), whereas in the late subgroup, a significant increase in left ventricle diameters was observed. Conclusion Our results first demonstrate in humans that in the early hours from the occlusion of the coronary artery, the extent and severity of the wall motion abnormalities inside the area at risk show large variability without relation to the elapsed time since the onset of symptoms. On the other hand, the results of follow-up echocardiography proved that the wall motion improvement was highly dependent on the ischemic time.