Suppression of Early and Late Afterdepolarizations by Heterozygous Knockout of the Na ⁺ /Ca ²⁺ Exchanger in a Murine Model

Abstract

Background-The Na + /Ca 2+ exchanger (NCX) has been implied to cause arrhythmias. To date, information on the role of NCX in arrhythmogenesis derived from models with increased NCX expression, hypertrophy, and heart failure. Furthermore, the exact mechanism by which NCX exerts its potentially proarrhythmic effect, ie, by promoting early afterdepolarization (EAD) or delayed afterdepolarization (DAD) or both, is unknown. Methods and Results-We investigated isolated cardiomyocytes from a murine model with heterozygous knockout of NCX (hetKO) using the patch clamp and Ca 2+ imaging techniques. Action potential duration was shorter in hetKO with I Ktot not being increased. The rate of spontaneous Ca 2+ release events and the rate of DADs were unaltered; however, DADs had lower amplitude in hetKO. A DAD triggered a spontaneous action potential significantly less often in hetKO when compared with wild-type. The occurrence of EADs was also drastically reduced in hetKO. I Ca activity was reduced in hetKO, an effect that was abolished in the presence of the Ca 2+ buffer BAPTA. Conclusions-Genetic suppression of NCX reduces both EADs and DADs. The following molecular mechanisms apply: (1) Although the absolute number of DADs is unaffected, an impaired translation of DADs into spontaneous action potentials results from a reduced DAD amplitude. (2) EADs are reduced in absolute number of occurrence, which is presumably a consequence of shortened action potential duration because of reduced NCX activity but also reduced I Ca the latter possibly being caused by a direct modulation of Ca 2+ -dependent I Ca inhibition by reduced NCX activity. This is the first study to demonstrate that genetic inhibition of NCX protects against afterdepolarizations and to investigate the underlying mechanisms. (Circ Arrhythm Electrophysiol.

Electrophysiological alterations in a murine model of chronic coxsackievirus B3 myocarditis

“…A similar mechanism has been shown by Pott et al where altered amplitudes of DADs and EADs were associated with an antiarrhythmic effect in NCX-KO mice [28]. However, it remains unclear which underlying mechanism mediates this difference in membrane potential in CVB3+ cardiomyocytes or whether the virus proteins themselves cause this alteration in CVB3+ cardiomyocytes.…”

Characterization of CaV1.2 exon 33 heterozygous knockout mice and negative correlation between Rbfox1 and CaV1.2 exon 33 expressions in human heart failure

“…Following that, we also measured the early after-depolarization (EAD) and autonomous action potentials (APs), two hallmarks of cardiac arrhythmias. 15,16 Our data showed the occurrence of EAD in exon 33…”

Triggered activity in atrial myocytes is influenced by Na+/Ca2+ exchanger activity in genetically altered mice

“…The protocol for immunoblot analysis and the quantification related to the housekeeping protein calsequestrin, was conducted as previously reported with minor modifications[9, 10]. …”

“…The patch-clamp setup and technical aspects of the measurement have been described previously [9]. Experimental protocols and solutions used for voltage- and current-clamp recordings are given in the online supplement.…”

“…Data was acquired and processed with Felix 1.42 (Photon Technologies Inc., South Brunswick, USA) as described previously[9]. Solutions and experimental protocols are given in the online material supplement.…”