Chronic Dantrolene Treatment Does Not Affect Hypertension, but Attenuates Sympathetic Stimulation Enhanced Atrial Fibrillation Inducibility in SHR

Effects of reversible SERCA inhibition on catecholamine exocytosis and intracellular [Ca2+] signaling in chromaffin cells from normotensive Wistar Kyoto rats and spontaneously hypertensive rats

Intracellular Ca2+ ([Ca2+]i) signaling and catecholamine (CA) exocytosis from adrenal chromaffin cells (CCs) differ between mammalian species. These differences partly result from the different contributions of Ca2+-induced Ca2+-release (CICR) from internal stores, which boosts intracellular Ca2+ signals. Transient inhibition of the sarcoendoplasmic reticulum (SERCA) Ca2+ pump with cyclopiazonic acid (CPA) reduces CICR. Recently, Martínez-Ramírez et al. found that CPA had contrasting effects on catecholamine secretion and intracellular Ca2+ signals in mouse and bovine CCs, where it enhanced and inhibited exocytosis, respectively. After CPA withdrawal, exocytosis diminished in mouse CCs and increased in bovine CCs. These differences can be explained if mouse CCs have weak CICR and strong Ca2+ uptake, and the reverse is true for bovine CCs. Surprisingly, CPA slightly reduced the amplitude of Ca2+ signals in both mouse and bovine CCs. Here we examined the effects of CPA on stimulated CA exocytosis and Ca2+ signaling in rat CCs and investigated if it alters differently the responses of CCs from normotensive (WKY) or hypertensive (SHR) rats, which differ in the gain of CICR. Our results demonstrate that CPA application strongly inhibits voltage-gated exocytosis and Ca2+ transients in rat CCs, regardless of strain (SHR or WKY). Thus, despite the greater phylogenetic distance from the most recent common ancestors, suppression of endoplasmic reticulum (ER) Ca2+ uptake through CPA inhibits the CA secretion in rat CCs more similarly to bovine than mouse CCs, unveiling divergent evolutionary relationships in the mechanism of CA exocytosis of CCs between rodents. Agents that inhibit the SERCA pump, such as CPA, suppress catecholamine secretion equally well in WKY and SHR CCs and are not potential therapeutic agents for hypertension. Rat CCs display Ca2+ signals of varying widths. Some even show early and late Ca2+ components. Narrowing the Ca2+ transients by CPA and ryanodine suggests that the late component is mainly due to CICR. Simultaneous recordings of Ca2+ signaling and amperometry in CCs revealed the existence of a robust and predictable correlation between the kinetics of the whole-cell intracellular Ca2+ signal and the rate of exocytosis at the single-cell level.

Molecular Insights in Atrial Fibrillation Pathogenesis and Therapeutics: A Narrative Review

The prevalence of atrial fibrillation (AF) is bound to increase globally in the following years, affecting the quality of life of millions of people, increasing mortality and morbidity, and beleaguering health care systems. Increasingly effective therapeutic options against AF are the constantly evolving electroanatomic substrate mapping systems of the left atrium (LA) and ablation catheter technologies. Yet, a prerequisite for better long-term success rates is the understanding of AF pathogenesis and maintenance. LA electrical and anatomical remodeling remains in the epicenter of current research for novel diagnostic and treatment modalities. On a molecular level, electrical remodeling lies on impaired calcium handling, enhanced inwardly rectifying potassium currents, and gap junction perturbations. In addition, a wide array of profibrotic stimuli activates fibroblast to an increased extracellular matrix turnover via various intermediaries. Concomitant dysregulation of the autonomic nervous system and the humoral function of increased epicardial adipose tissue (EAT) are established mediators in the pathophysiology of AF. Local atrial lymphomononuclear cells infiltrate and increased inflammasome activity accelerate and perpetuate arrhythmia substrate. Finally, impaired intracellular protein metabolism, excessive oxidative stress, and mitochondrial dysfunction deplete atrial cardiomyocyte ATP and promote arrhythmogenesis. These overlapping cellular and molecular alterations hinder us from distinguishing the cause from the effect in AF pathogenesis. Yet, a plethora of therapeutic modalities target these molecular perturbations and hold promise in combating the AF burden. Namely, atrial selective ion channel inhibitors, AF gene therapy, anti-fibrotic agents, AF drug repurposing, immunomodulators, and indirect cardiac neuromodulation are discussed here.

Anthracycline-induced cardiomyopathy: cellular and molecular mechanisms

Despite the known risk of cardiotoxicity, anthracyclines are widely prescribed chemotherapeutic agents. They are broadly characterized as being a robust effector of cellular apoptosis in rapidly proliferating cells through its actions in the nucleus and formation of reactive oxygen species (ROS). And, despite the early use of dexrazoxane, no effective treatment strategy has emerged to prevent the development of cardiomyopathy, despite decades of study, suggesting that much more insight into the underlying mechanism of the development of cardiomyopathy is needed. In this review, we detail the specific intracellular activities of anthracyclines, from the cell membrane to the sarcoplasmic reticulum, and highlight potential therapeutic windows that represent the forefront of research into the underlying causes of anthracycline-induced cardiomyopathy.