Action potential variability in human pluripotent stem cell-derived cardiomyocytes obtained from healthy donors.

Human pluripotent stem cells (PSC) have been used for disease modelling, after differentiation into the desired cell type. Electrophysiologic properties of cardiomyocytes derived from pluripotent stem cells are extensively used to model cardiac arrhythmias, in cardiomyopathies and channelopathies. This requires strict control of the multiple variables that can influence the electrical properties of these cells. In this article, we report the action potential variability of 780 cardiomyocytes derived from pluripotent stem cells obtained from six healthy donors. We analyze the overall distribution of action potential (AP) data, the distribution of action potential data per cell line, per differentiation protocol and batch. This analysis indicates that even using the same cell line and differentiation protocol, the differentiation batch still affects the results. This variability has important implications in modeling arrhythmias and imputing pathogenicity to variants encountered in patients with arrhythmic diseases. We conclude that even when using isogenic cell lines to ascertain pathogenicity to variants associated to arrythmias one should use cardiomyocytes derived from pluripotent stem cells using the same differentiation protocol and batch and pace the cells or use only cells that have very similar spontaneous beat rates. Otherwise, one may find phenotypic variability that is not attributable to pathogenic variants.

Thyroid stimulating hormone directly modulates cardiac electrical activity.

BACKGROUND: The electrocardiogram of hypothyroid patients shows a series of abnormalities of cardiac repolarization due to a reduction of some repolarizing K(+) currents and an increase of the L-type calcium current. Experimental and clinical works call into question the unique role of T3 and T4 in these mechanisms and correlate increased serum TSH levels with the repolarization abnormalities in patients with both subclinical and overt hypothyroidism. In this context, the aim of the present study was to investigate the direct effects of TSH upon cardiac electrical properties. METHODS: The action potential recording and the ion channel subunits mRNA expression were obtained from left ventricle of adult rats. Additionally, the repolarizing K(+) currents and the L-type Ca(2+) current (ICa-L) were recorded in isolated rat adult ventricular myocytes by the patch-clamp technique. RESULTS: 24h exposure to TSH lengthened the action potential and slightly depolarized the resting membrane potential. TSH- receptor activation causes a reduction of the amplitude of Ito and IK1 currents caused by a reduction in channels expression. However, TSH had no effect on ICa-L, IK or IKur. CONCLUSION: These results support the idea that some of the electrical disturbances seen in hypothyroid hearts, such as the Ito and IK1 current reduction, could be caused not by low T3 but by the elevation of circulating TSH.

MicroRNAs: potential therapeutic targets in diabetic complications of the cardiovascular and renal systems.

Diabetes mellitus is a serious health problem that can lead to several pathological complications in numerous organs and tissues. The most important and most prevalent organs affected by this disease are the heart and the kidneys, and these complications are the major causes of death in patients with diabetes. MicroRNAs (miRNAs), short non-coding RNAs, have been found to be functionally important in the regulation of several pathological processes, and they are emerging as an important therapeutic tool to avoid the complications of diabetes mellitus. This review summarizes the knowledge on the effects of miRNAs in diabetes. The use of miRNAs in diabetes from a clinical perspective is also discussed, focusing on their potential role to repair cardiovascular and renal complications.

Cardiac effects of anabolic steroids: hypertrophy, ischemia and electrical remodelling as potential triggers of sudden death.

Anabolic-androgenic steroids (AAS) are synthetic testosterone derivatives developed to maximise anabolic activity and minimise androgenic activity. AAS abuse is widespread among both athletes and non-athletes at fitness centres and is becoming a public health issue. In addition to their atherogenic, thrombogenic and spastic effects, AAS have direct cardiotoxic effects by causing hypertrophy, electrical and structural remodelling, and contractile dysfunction and by increasing the susceptibility to ischemic injuries. All of these factors contribute to an increased risk of ventricular arrhythmias and sudden cardiac death.

The negative inotropic action of canrenone is mediated by L-type calcium current blockade and reduced intracellular calcium transients.

BACKGROUND AND PURPOSE: Adding spironolactone to standard therapy in heart failure reduces morbidity and mortality, but the underlying mechanisms are not fully understood. We analysed the effect of canrenone, the major active metabolite of spironolactone, on myocardial contractility and intracellular calcium homeostasis. EXPERIMENTAL APPROACH: Left ventricular papillary muscles and cardiomyocytes were isolated from male Wistar rats. Contractility of papillary muscles was assessed with force transducers, Ca(2+) transients by fluorescence and Ca(2+) fluxes by electrophysiological techniques. KEY RESULTS: Canrenone (300-600 micromol L(-1)) reduced developed tension, maximum rate of tension increase and maximum rate of tension decay of papillary muscles. In cardiomyocytes, canrenone (50 micromol L(-1)) reduced cell shortening and L-type Ca(2+) channel current, whereas steady-state activation and inactivation, and reactivation curves were unchanged. Canrenone also decreased the Ca(2+) content of the sarcoplasmic reticulum, intracellular Ca(2+) transient amplitude and intracellular diastolic Ca(2+) concentration. However, the time course of [Ca(2+)](i) decline during transients evoked by caffeine was not affected by canrenone. CONCLUSION AND IMPLICATIONS: Canrenone reduced L-type Ca(2+) channel current, amplitude of intracellular Ca(2+) transients and Ca(2+) content of sarcoplasmic reticulum in cardiomyocytes. These changes are likely to underlie the negative inotropic effect of canrenone.