The Effects of SEA0400 on Ca2+ Transient Amplitude and Proarrhythmia Depend on the Na+/Ca2+ Exchanger Expression Level in Murine Models

Abstract

Background/Objective: The cardiac Na+/Ca2+ exchanger (NCX) has been identified as a promising target to counter arrhythmia in previous studies investigating the benefit of NCX inhibition. However, the consequences of NCX inhibition have not been investigated in the setting of altered NCX expression and function, which is essential, since major cardiac diseases (heart failure/atrial fibrillation) exhibit NCX upregulation. Thus, we here investigated the effects of the NCX inhibitor SEA0400 on the Ca2+ transient amplitude and on proarrhythmia in homozygous NCX overexpressor (OE) and heterozygous NCX knockout (hetKO) mice compared to corresponding wild-types (WTOE/WThetKO).Methods/Results: Ca2+ transients of field-stimulated isolated ventricular cardiomyocytes were recorded with fluo-4-AM or indo-1-AM. SEA0400 (1 μM) significantly reduced NCX forward mode function in all mouse lines. SEA0400 (1 μM) significantly increased the amplitude of field-stimulated Ca2+ transients in WTOE, WThetKO, and hetKO, but not in OE (% of basal; OE = 98.7 ± 5.0; WTOE = 137.8 ± 5.2*; WThetKO = 126.3 ± 6.0*; hetKO = 140.6 ± 12.8*; *p < 0.05 vs. basal). SEA0400 (1 μM) significantly reduced the number of proarrhythmic spontaneous Ca2+ transients (sCR) in OE, but increased it in WTOE, WThetKO and hetKO (sCR per cell; basal/+SEA0400; OE = 12.5/3.7; WTOE = 0.2/2.4; WThetKO = 1.3/8.8; hetKO = 0.2/5.5) and induced Ca2+ overload with subsequent cell death in hetKO.Conclusion: The effects of SEA0400 on Ca2+ transient amplitude and the occurrence of spontaneous Ca2+ transients as a proxy measure for inotropy and cellular proarrhythmia depend on the NCX expression level. The antiarrhythmic effect of SEA0400 in conditions of increased NCX expression promotes the therapeutic concept of NCX inhibition in heart failure/atrial fibrillation. Conversely, in conditions of reduced NCX expression, SEA0400 suppressed the NCX function below a critical level leading to adverse Ca2+ accumulation as reflected by an increase in Ca2+ transient amplitude, proarrhythmia and cell death. Thus, the remaining NCX function under inhibition may be a critical factor determining the inotropic and antiarrhythmic efficacy of SEA0400.

Distinct Occurrence of Proarrhythmic Afterdepolarizations in Atrial Versus Ventricular Cardiomyocytes: Implications for Translational Research on Atrial Arrhythmia

“…The methods to isolate atrial and ventricular cardiomyocytes have been reported in former studies ( Bögeholz et al, 2016 , 2017 ). In brief, mice were euthanized by carbon dioxide inhalation and excised hearts were retrogradely perfused via the aorta using a modified Langendorff apparatus.…”

Proarrhythmic Remodeling of Calcium Homeostasis in Cardiac Disease; Implications for Diabetes and Obesity

“…Pharmacological inhibition of NCX1 is generally viewed as beneficial since it reduces Ca 2+ influx during reverse mode limiting Ca 2+ overload and attenuates depolarization during forward mode reducing triggered activity ( Antoons et al, 2012 ). However, if NCX1 is already diminished as shown in many models of diabetes ( Makino et al, 1987 ; Pierce et al, 1990 ; Golfman et al, 1998 ; Hattori et al, 2000 ) additional inhibition was proven to be detrimental leading to adverse accumulation of Ca 2+ in cytosol and cell death ( Bögeholz et al, 2017 ).…”

Targeting Ca2 + Handling Proteins for the Treatment of Heart Failure and Arrhythmias

“…This differential arrhythmic effect may be dependent on the expression levels of NCX. A study found SEA-0400 to be antiarrhythmic in mouse models with increased NCX expression, such as HF and AF, but in conditions with reduced NCX expression, SEA-0400 was found to increase Ca 2+ transient amplitude and spontaneous Ca 2+ transients, ultimately acting proarrhythmic (Bogeholz et al, 2017). These findings suggest that in clinical conditions in which NCX function is reduced, such as diabetic cardiomyopathy, further NCX inhibition could trigger arrhythmias by reducing NCX function below the level required for balanced Ca 2+ dynamics (Bogeholz et al, 2017).…”