RESEARCH ARTICLE The Effect of a Novel Highly Selective Inhibitor of the Sodium/Calcium Exchanger (NCX) on Cardiac Arrhythmias in In Vitro and In Vivo Experiments Zso ´ fia Kohajda 2 , Nikolett Farkas-Morvay 1 , Norbert Jost 2,3 , Norbert Nagy 2 , Amir Geramipour 1 , Andra ´ s Horva ´th 1,2 , Richa ´ rd S. Varga 1 , Tibor Hornyik 1 , Claudia Corici 1 , Ka ´ roly Acsai 2 , Bala ´ zs Horva ´th 4 , Ja ´ nos Prorok 1 , Bala ´ zs O ¨ rdo ¨g 1 , Szilvia De ´ri 1 , Da ´ niel To ´th 2 , Jouko Levijoki 6 , Piero Pollesello 6 , Tuula Koskelainen 6 , Leena Otsomaa 6 , Andra ´sTo ´ th 1,2 , Istva ´ n Baczko ´ 1,3 , Istva ´ n Lepra ´n 1 , Pe ´ ter P. Na ´na ´si 4,5 , Julius Gy Papp 1,2 , Andra ´ s Varro ´ 1,2‡ , La ´szlo ´ Vira ´g 1,2‡ * 1 Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, Szeged, Hungary, 2 MTA-SZTE Research Group of Cardiovascular Pharmacology, Hungarian Academy of Sciences, Szeged, Hungary, 3 Department of Pathophysiology, "Victor Babes" University of Medicine and Pharmacy, Timisoara, Romania, 4 Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary, 5 Department of Dental Physiology and Pharmacology, Faculty of Dentistry, University of Debrecen, Debrecen, Hungary, 6 Orion Pharma, Espoo, Finland ‡ These authors share senior authorship on this work. * varro.andras@med.u-szeged.hu Abstract Background In this study the effects of a new, highly selective sodium-calcium exchanger (NCX) inhibi- tor, ORM-10962 were investigated on cardiac NCX current, Ca 2+ transients, cell shortening and in experimental arrhythmias. The level of selectivity of the novel inhibitor on several major transmembrane ion currents (L-type Ca 2+ current, major repolarizing K + currents, late Na + current, Na + /K + pump current) was also determined. Methods Ion currents in single dog ventricular cells (cardiac myocytes; CM), and action potentials in dog cardiac multicellular preparations were recorded utilizing the whole-cell patch clamp and standard microelectrode techniques, respectively. Ca 2+ transients and cell shortening were measured in fluorescent dye loaded isolated dog myocytes. Antiarrhythmic effects of ORM-10962 were studied in anesthetized ouabain (10 μg/kg/min i.v.) pretreated guinea pigs and in ischemia-reperfusion models (I/R) of anesthetized coronary artery occluded rats and Langendorff perfused guinea pigs hearts. Results ORM-10962 significantly reduced the inward/outward NCX currents with estimated EC50 values of 55/67 nM, respectively. The compound, even at a high concentration of 1 μM, did PLOS ONE | DOI:10.1371/journal.pone.0166041 November 10, 2016 1 / 28 a11111 OPEN ACCESS Citation: Kohajda Z, Farkas-Morvay N, Jost N, Nagy N, Geramipour A, Horva ´th A, et al. (2016) The Effect of a Novel Highly Selective Inhibitor of the Sodium/Calcium Exchanger (NCX) on Cardiac Arrhythmias in In Vitro and In Vivo Experiments. PLoS ONE 11(11): e0166041. doi:10.1371/journal. pone.0166041 Editor: Thomas Hund, The Ohio State University, UNITED STATES Received: April 20, 2016 Accepted: October 21, 2016 Published: November 10, 2016 Copyright: © 2016 Kohajda et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper. Funding: This work was supported by grants from the Hungarian Scientific Research Fund (OTKA NK- 104331 for AV, K100151 for IB, NN-109904 for NJ and ANN-113273 for AT), National Office for Research and Technology- Baross and A ´ nyos Jedlik Programmes (REG-DA-09-2-2009-0115- NCXINHIB for NJ and AT and NKFP_07_01- RYT07_AF for AV and NJ), the Hungarian Academy of Sciences (for AV, NJ and AT), the Ministry of