BACKGROUND AND PURPOSEAt present there are no small molecule inhibitors that show strong selectivity for the Na + /Ca 2+ exchanger (NCX). Hence, we studied the electrophysiological effects of acute administration of ORM-10103, a new NCX inhibitor, on the NCX and L-type Ca 2+ currents and on the formation of early and delayed afterdepolarizations. EXPERIMENTAL APPROACHIon currents were recorded by using a voltage clamp technique in canine single ventricular cells, and action potentials were obtained from canine and guinea pig ventricular preparations with the use of microelectrodes. KEY RESULTSORM-10103 significantly reduced both the inward and outward NCX currents. Even at a high concentration (10 μM), ORM-10103 did not significantly change the L-type Ca 2+ current or the maximum rate of depolarization (dV/dtmax), indicative of the fast inward Na + current. At 10 μM ORM-10103 did not affect the amplitude or the dV/dtmax of the slow response action potentials recorded from guinea pig papillary muscles, which suggests it had no effect on the L-type Ca 2+ current. ORM-10103 did not influence the Na + /K + pump or the main K + currents of canine ventricular myocytes, except the rapid delayed rectifier K + current, which was slightly diminished by the drug at 3 μM. The amplitudes of pharmacologically-induced early and delayed afterdepolarizations were significantly decreased by ORM-10103 (3 and 10 μM) in a concentration-dependent manner. CONCLUSIONS AND IMPLICATIONSORM-10103 is a selective inhibitor of the NCX current and can abolish triggered arrhythmias. Hence, it has the potential to be used to prevent arrhythmogenic events. LINKED ARTICLE

BackgroundIn this study the effects of a new, highly selective sodium-calcium exchanger (NCX) inhibitor, ORM-10962 were investigated on cardiac NCX current, Ca2+ transients, cell shortening and in experimental arrhythmias. The level of selectivity of the novel inhibitor on several major transmembrane ion currents (L-type Ca2+ current, major repolarizing K+ currents, late Na+ current, Na+/K+ pump current) was also determined.MethodsIon 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. Ca2+ 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.ResultsORM-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 not modify significantly the magnitude of ICaL in CMs, neither had any apparent influence on the inward rectifier, transient outward, the rapid and slow components of the delayed rectifier potassium currents, the late and peak sodium and Na+/K+ pump currents. NCX inhibition exerted moderate positive inotropic effect under normal condition, negative inotropy when reverse, and further positive inotropic effect when forward mode was facilitated. In dog Purkinje fibres 1 μM ORM-10962 decreased the amplitude of digoxin induced delayed afterdepolarizations (DADs). Pre-treatment with 0.3 mg/kg ORM-10962 (i.v.) 10 min before starting ouabain infusion significantly delayed the development and recurrence of ventricular extrasystoles (by about 50%) or ventricular tachycardia (by about 30%) in anesthetized guinea pigs. On the contrary, ORM-10962 pre-treatment had no apparent influence on the time of onset or the severity of I/R induced arrhythmias in anesthetized rats and in Langendorff perfused guinea-pig hearts.ConclusionsThe present study provides strong evidence for a high efficacy and selectivity of the NCX-inhibitory effect of ORM-10962. Selective NCX inhibition can exert positive as well as negative inotropic effect depending on the actual operation mode of NCX. Selective NCX blockade may contribute to the prevention of DAD based arrhythmogenesis, in vivo, however, its effect on I/R induced arrhythmias is still uncertain.

AimsHeart failure with preserved ejection fraction (HFpEF) is increasingly common but there is currently no established pharmacological therapy. We hypothesized that ORM‐11035, a novel specific Na+/Ca2+ exchanger (NCX) inhibitor, improves cardiac function and remodelling independent of effects on arterial blood pressure in a model of cardiorenal HFpEF.Methods and resultsRats were subjected to subtotal nephrectomy (NXT) or sham operation. Eight weeks after intervention, treatment for 16 weeks with ORM‐11035 (1 mg/kg body weight) or vehicle was initiated. At 24 weeks, blood pressure measurements, echocardiography and pressure–volume loops were performed. Contractile function, Ca2+ transients and NCX‐mediated Ca2+ extrusion were measured in isolated ventricular cardiomyocytes. NXT rats (untreated) showed a HFpEF phenotype with left ventricular (LV) hypertrophy, LV end‐diastolic pressure (LVEDP) elevation, increased brain natriuretic peptide (BNP) levels, preserved ejection fraction and pulmonary congestion. In cardiomyocytes from untreated NXT rats, early relaxation was prolonged and NCX‐mediated Ca2+ extrusion was decreased. Chronic treatment with ORM‐11035 significantly reduced LV hypertrophy and cardiac remodelling without lowering systolic blood pressure. LVEDP [14 ± 3 vs. 9 ± 2 mmHg; NXT (n = 12) vs. NXT + ORM (n = 12); P = 0.0002] and BNP levels [71 ± 12 vs. 49 ± 11 pg/mL; NXT (n = 12) vs. NXT + ORM (n = 12); P < 0.0001] were reduced after ORM treatment. LV cardiomyocytes from ORM‐treated rats showed improved active relaxation and diastolic cytosolic Ca2+ decay as well as restored NCX‐mediated Ca2+ removal, indicating NCX modulation with ORM‐11035 as a promising target in the treatment of HFpEF.ConclusionChronic inhibition of NCX with ORM‐11035 significantly attenuated cardiac remodelling and diastolic dysfunction without lowering systemic blood pressure in this model of HFpEF. Therefore, long‐term treatment with selective NCX inhibitors such as ORM‐11035 should be evaluated further in the treatment of heart failure.

Na/Ca exchanger (NCX) is the main Ca transporter in cardiac myocytes. Its inhibition could be expected to exert positive inotropic action by accumulation of cytosolic Ca ([Ca]). However, we have observed only a marginal positive inotropic effect upon selective inhibition of NCX, which was enhanced when forward activity was facilitated. Here we attempted to clarify the underlying mechanism of the limited inotropic action of selective NCX inhibition by a novel inhibitor ORM-10962 on canine ventricular myocytes. 1µM ORM-10962 reduced the Ca content of sarcoplasmic reticulum (SR) when the reverse NCX was favoured, while SR Ca content was increased by ORM-10962 under conditions favouring the forward activity, like elevation of [Ca]. L-type Ca current (I) was not affected by 1µM ORM-10962 in the absence of SR Ca release, while I was suppressed by ORM-10962 during normal Ca cycling. The apparent degree of forward NCX inhibition was dependent on the elevation of [Ca], suggesting that an increased driving force of forward NCX can also limit the accumulation of [Ca]. We concluded that in healthy myocardium the possible positive inotropic potential of NCX inhibition is considerably weaker than it was expected earlier by theoretical assumptions. The underlying mechanism may involve the autoregulation of Ca handling and/or the preserved inducibility of forward NCX by high [Ca]. This limitation of selective NCX inhibition seen in undiseased myocardium requires further studies in failing heart, which may allow correct evaluation of the potential therapeutic value of selective NCX inhibitors in the treatment of heart failure.

Background and purpose The lack of selective sodium-calcium exchanger (NCX) inhibitors has hampered the exploration of physiological and pathophysiological roles of cardiac NCX 1.1. We aimed to discover more potent and selective drug like NCX 1.1. inhibitor. Experimental approach A flavan series-based pharmacophore model was constructed. Virtual screening helped us identify a novel scaffold for NCX inhibition. A distinctively different NCX 1.1 inhibitor, ORM-11372, was discovered after lead optimization. Its potency against human and rat NCX 1.1 and selectivity against other ion channels was assessed. The cardiovascular effects of ORM-11372 were studied in normal and infarcted rats, and rabbits. Human cardiac safety was studied ex-vivo using human ventricular trabeculae. Key results ORM-11372 inhibited human NCX 1.1 reverse and forward currents; IC 50 values were 5 and 6 nM, respectively. ORM-11372 inhibited human cardiac sodium 1.5 (I Na) and hERG K V 11.1 currents (I hERG) in a concentration-dependent manner; IC 50 values were 23.2 and 10.0 µM. ORM-11372 caused no changes in action potential duration; short term variability and triangulation were observed for concentrations of upto 10 µM. ORM-11372 induced positive inotropic effects in 18 ± 6% and 35 ± 8% anesthetized rats with myocardial infarctions and rabbits, respectively; no other haemodynamic effects were observed, except improved relaxation at the lowest dose.