Compartmentalized β1-adrenergic signalling synchronizes excitation-contraction coupling without modulating individual Ca2+ sparks in healthy and hypertrophied cardiomyocytes

Sodium–Glucose cotransporter 2 inhibitor empagliflozin decreases ventricular arrhythmia susceptibility by alleviating electrophysiological remodeling post-myocardial-infarction in mice

Background: Recent clinical trials indicate that sodium–glucose cotransporter 2 (SGLT2) inhibitors improve cardiovascular outcomes in myocardial infarction (MI) patients, but the underlying mechanisms remain unknown. As arrhythmia often occurs during myocardial infarction, it is the main cause of death.

Objective: The purpose of this study was to investigate the influence of empagliflozin (EMPA), an SGLT2 inhibitor, on cardiac electrophysiological remodeling and arrhythmia susceptibility of myocardial infarction mice.

Methods: ECG was obtained from mice 1 week after MI to determine the QT interval. In an electrophysiological study and optical mapping was performed to evaluate the function of EMPA and underlying mechanisms of post-myocardial-infarction in mice.

Results: EMPA treatment significantly reduced the QT interval of MI mice (MI + EMPA 50.24 ms vs. MI 64.68 ms). The membrane potential and intracellular Ca [Ca_i] were mapped from 13 MI hearts and five normal hearts using an optical mapping technique. A dynamic pacing protocol was used to determine action potential duration and [Ca_i] at baseline and after EMPA (10 umol/L) infusion. EMPA perfusion did not change the APD₈₀ and CaT₈₀ in normal ventricles while shortening them in an infarct zone, bordering zone, and remote zone of MI hearts at 200 ms, 150 ms, 120 ms, and 100 ms pacing cycle length. The conduction velocity of infarcted ventricles was 0.278 m/s and 0.533 m/s in normal ventricles at baseline (p < 0.05). After EMPA administration, the conduction velocity of infarcted ventricles increased to 0.363 m/s, whereas no significant changes were observed in normal ventricles. The action potential rise time, CaT rise time, and CaT tau time were improved after EMPA perfusion in infarcted ventricles, whereas no significant changes were observed in normal ventricles. EMPA decreases early afterdepolarizations premature ventricular beats, and ventricular fibrillation (VF) in infarcted ventricles. The number of phase singularities (baseline versus EMPA, 6.26 versus 3.25), dominant frequency (20.52 versus 10.675 Hz), and ventricular fibrillation duration (1.072 versus 0.361 s) during ventricular fibrillation in infarcted ventricles were all significantly decreased by EMPA.

Conclusion: Treatment with EMPA improved post-MI electrophysiological remodeling and decreased substrate for VF of MI mice. The inhibitors of SGLT2 may be a new class of agents for the prevention of ventricle arrhythmia after chronic MI.

Adrenoceptor sub-type involvement in Ca2+ current stimulation by noradrenaline in human and rabbit atrial myocytes

Atrial fibrillation (AF) from elevated adrenergic activity may involve increased atrial L-type Ca²⁺ current (I_CaL) by noradrenaline (NA). However, the contribution of the adrenoceptor (AR) sub-types to such I_CaL-increase is poorly understood, particularly in human. We therefore investigated effects of various broad-action and sub-type-specific α- and β-AR antagonists on NA-stimulated atrial I_CaL. I_CaL was recorded by whole-cell-patch clamp at 37 °C in myocytes isolated enzymatically from atrial tissues from consenting patients undergoing elective cardiac surgery and from rabbits. NA markedly increased human atrial I_CaL, maximally by ~ 2.5-fold, with EC₇₅ 310 nM. Propranolol (β₁ + β₂-AR antagonist, 0.2 microM) substantially decreased NA (310 nM)-stimulated I_CaL, in human and rabbit. Phentolamine (α₁ + α₂-AR antagonist, 1 microM) also decreased NA-stimulated I_CaL. CGP20712A (β₁-AR antagonist, 0.3 microM) and prazosin (α₁-AR antagonist, 0.5 microM) each decreased NA-stimulated I_CaL in both species. ICI118551 (β₂-AR antagonist, 0.1 microM), in the presence of NA + CGP20712A, had no significant effect on I_CaL in human atrial myocytes, but increased it in rabbit. Yohimbine (α₂-AR antagonist, 10 microM), with NA + prazosin, had no significant effect on human or rabbit I_CaL. Stimulation of atrial I_CaL by NA is mediated, based on AR sub-type antagonist responses, mainly by activating β₁- and α₁-ARs in both human and rabbit, with a β₂-inhibitory contribution evident in rabbit, and negligible α₂ involvement in either species. This improved understanding of AR sub-type contributions to noradrenergic activation of atrial I_CaL could help inform future potential optimisation of pharmacological AR-antagonism strategies for inhibiting adrenergic AF.