Nils Bögeholz1, Paul Pauls2, B Klemens Bauer2, Jan S Schulte2, Dirk G Dechering2, Gerrit Frommeyer2, Uwe Kirchhefer2, Joshua I Goldhaber2, Frank U Müller2, Lars Eckardt2, Christian Pott2. 1. From the Division of Electrophysiology, Department of Cardiovascular Medicine (N.B., P.P., B.K.B., D.G.D., G.F., L.E., C.P.) and Institute of Pharmacology and Toxicology (P.P., B.K.B., J.S.S., U.K., F.U.M.), University Hospital Münster, Münster, Germany; and Heart Institute, Cedars-Sinai Medical Center, Los Angeles, CA (J.I.G.). nils.boegeholz@ukmuenster.de. 2. From the Division of Electrophysiology, Department of Cardiovascular Medicine (N.B., P.P., B.K.B., D.G.D., G.F., L.E., C.P.) and Institute of Pharmacology and Toxicology (P.P., B.K.B., J.S.S., U.K., F.U.M.), University Hospital Münster, Münster, Germany; and Heart Institute, Cedars-Sinai Medical Center, Los Angeles, CA (J.I.G.).
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 IKtot 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. ICa 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 ICa the latter possibly being caused by a direct modulation of Ca(2+)-dependent ICa 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.
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 IKtot 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. ICa 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 ICa the latter possibly being caused by a direct modulation of Ca(2+)-dependent ICa 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.
Authors: N Bögeholz; P Pauls; S Kaese; J S Schulte; M D Lemoine; D G Dechering; G Frommeyer; J I Goldhaber; M D Seidl; U Kirchhefer; L Eckardt; F U Müller; C Pott Journal: J Mol Cell Cardiol Date: 2016-11-09 Impact factor: 5.000
Authors: Lili Wang; Kyungsoo Kim; Shan Parikh; Adrian Gabriel Cadar; Kevin R Bersell; Huan He; Jose R Pinto; Dmytro O Kryshtal; Bjorn C Knollmann Journal: J Mol Cell Cardiol Date: 2017-12-05 Impact factor: 5.000
Authors: Harsha D Devalla; Roselle Gélinas; Elhadi H Aburawi; Abdelaziz Beqqali; Philippe Goyette; Christian Freund; Marie-A Chaix; Rafik Tadros; Hui Jiang; Antony Le Béchec; Jantine J Monshouwer-Kloots; Tom Zwetsloot; Georgios Kosmidis; Frédéric Latour; Azadeh Alikashani; Maaike Hoekstra; Jurg Schlaepfer; Christine L Mummery; Brian Stevenson; Zoltan Kutalik; Antoine Af de Vries; Léna Rivard; Arthur Am Wilde; Mario Talajic; Arie O Verkerk; Lihadh Al-Gazali; John D Rioux; Zahurul A Bhuiyan; Robert Passier Journal: EMBO Mol Med Date: 2016-12-01 Impact factor: 12.137
Authors: J S Schulte; E Fehrmann; M A Tekook; D Kranick; B Fels; N Li; X H T Wehrens; A Heinick; M D Seidl; W Schmitz; F U Müller Journal: Basic Res Cardiol Date: 2016-01-27 Impact factor: 17.165