Effects of SEA0400, a novel inhibitor of the Na+/Ca2+ exchanger, on myocardial stunning in anesthetized dogs

Activation of the Na+/Ca2+ exchanger may contribute to Ca2+ overload during reperfusion after transient ischemia. We examined the effects of 2-[4-[(2,5-difluorophenyl) methoxy]phenoxy]-5-ethoxyaniline (SEA0400), a selective inhibitor of Na+/Ca2+ exchange, on a canine model of ischemia/reperfusion injury (myocardial stunning). Myocardial stunning was induced by a 15-min occlusion of the left anterior descending coronary artery followed by a 4-h reperfusion in anesthetized open-chest dogs. Reperfusion gradually restored myocardial percent segment shortening but remained depressed during a 4-h reperfusion period. A bolus intravenous injection of SEA0400 (0.3 or 1.0 mg/kg), given 1 min before reperfusion, improved significantly the recovery of percent segment shortening in the ischemic/reperfused myocardium. SEA0400 did not affect the hemodynamics and electrocardiogram parameters. In addition, SEA0400 did not affect reperfusion-induced change in coronary blood flow. These results suggest that the Na+/Ca2+ exchanger is involved in the stunned myocardium of dogs after reperfusion, and that SEA0400 has a protective effect against myocardial stunning in dogs.     

Cardioprotective effect of SEA0400, a selective inhibitor of the Na(+)/Ca(2+) exchanger, on myocardial ischemia-reperfusion injury in rats

In this study, we investigated whether the Na(+)/Ca(2+) exchanger (NCX) inhibitor SEA0400 (2-[4-[(2,5-difluorophenyl)methoxy]phenoxy-5-ethoxyaniline) might have a protective effect against myocardial ischemia-reperfusion injury in rats. In particular, we focused on cardiac function using Doppler echocardiography and cardiac gene expression. We intravenously administered either SEA0400 and delivery vehicle or only the vehicle (as a control) to Wistar rats 5 min before ischemia was induced. Reperfusion was performed after 30 min of ischemia. At 1 week after ischemia-reperfusion injury, we assessed hemodynamics by inserting a polyethylene-tubing catheter, cardiac function by Doppler echocardiography, and myocardial mRNA expression was determined by Northern blot analysis. Left ventricular (LV) end-diastolic dimensions (LVDd) and LV end-diastolic volume (LVEDV) were significantly increased in the ischemia-reperfusion rat model group compared to the control group. The SEA0400-treated group had a significantly attenuated LVDd (P<0.05) and LVEDV (P<0.01) increase, compared to the vehicle-treated group. A decrease in the LV ejection fraction (P<0.05) was significantly prevented in the SEA0400-treated group compared to the vehicle-treated group. Moreover, mRNA expression of plasminogen activator inhibitor-1 in the non-infarcted LV of the SEA0400-treated group was significantly lower than in the vehicle-treated group (P<0.05). This study demonstrates that the NCX is an important mechanism for cell death in myocardial ischemia and reperfusion in rats. SEA0400 may prove to be a promising new drug in the clinical treatment of myocardial ischemia and reperfusion.     

Inhibition by SEA0400, a selective inhibitor of Na+/Ca2+ exchanger, of Na+ -dependent Ca2+ uptake and catecholamine release in bovine adrenal chromaffin cells

The effects of SEA0400, a selective inhibitor of the Na(+)/Ca(2+) exchanger (NCX), on Na(+)-dependent Ca(2+) uptake and catecholamine (CA) release were examined in bovine adrenal chromaffin cells that were loaded with Na(+) by treatment with ouabain and veratridine. SEA0400 inhibited Na(+)-dependent (45)Ca(2+) uptake and CA release, with the IC(50) values of 40 and 100 nM, respectively. The IC(50) values of another NCX inhibitor KB-R7943 were 1.8 and 3.7 microM, respectively. These results indicate that SEA0400 is about 40 times more potent than KB-R7943 in inhibiting NCX working in the reverse mode. In intact cells, SEA0400 and KB-R7943 inhibited CA release induced by acetylcholine and DMPP. The IC(50) values of SEA0400 were 5.1 and 4.5 microM and the values of KB-R7943 were 2.6 and 2.1 microM against the release induced by acetylcholine and DMPP, respectively, indicating that the potency of SEA0400 is about a half of that of KB-R7943 in inhibiting the nicotinic receptor-mediated CA release. The binding of [(3)H]nicotine with nicotinic receptors was inhibited by SEA0400 (IC(50) = 90 microM) and KB-R7943 (IC(50) = 12 microM). From these results, it is concluded that unlike KB-R7943, SEA0400 has a potent and selective action on NCX in bovine adrenal chromaffin cells.     

A novel and selective Na+/Ca2+ exchange inhibitor, SEA0400, improves ischemia/reperfusion-induced renal injury

We evaluated the effects of SEA0400 (2-[4-[(2,5-difluorophenyl)methoxy]phenoxy]-5-ethoxyaniline), a novel and selective Na+/Ca2+ exchange inhibitor, on ischemic acute renal failure. Ischemic acute renal failure in rats was induced by clamping the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after the contralateral nephrectomy. SEA0400 administration (0.3, 1 and 3 mg/kg, i.v.) before ischemia dose-dependently attenuated the ischemia/reperfusion-induced renal dysfunction and histological damage such as tubular necrosis. SEA0400 pretreatment at the higher dose suppressed the increment of renal endothelin-1 content after reperfusion. The ischemia/reperfusion-induced renal dysfunction was also overcome by post-ischemia treatment with SEA0400 at 3 mg/kg, i.v. In in vitro study, SEA0400 (0.2 and 1 microM) protected cultured porcine tubular cells (LLC-PK1) from hypoxia/reoxygenation-induced cell injury. These findings support the view that Ca2+ overload via the reverse mode of Na+/Ca2+ exchange, followed by endothelin-1 overproduction, plays an important role in the pathogenesis of ischemia/reperfusion-induced renal injury. The possibility exists that a selective Na+/Ca2+ exchange inhibitor such as SEA0400 is useful as effective therapeutic agent against ischemic acute renal failure in humans.     

A selective inhibitor of Na+/Ca2+ exchanger, SEA0400, preserves cardiac function and high-energy phosphates against ischemia/reperfusion injury

The Ca2+ overload by Ca2+ influx via Na+/Ca2+ exchanger (NCX) is a critical mechanism in myocardial ischemia/reperfusion injury. We investigated protective effects of a novel selective inhibitor of NCX, SEA0400, on cardiac function and energy metabolism during ischemia and reperfusion. Langendorff-perfused rat hearts were exposed to 35 minutes global ischemia and 40 minutes reperfusion. Using 31P nuclear magnetic resonance spectroscopy, cardiac phosphocreatine (PCr), ATP, and pHi were monitored. SEA0400 did not change the basic cardiac function, but improved the recovery of left ventricular developed pressure (LVDP) after reperfusion (27.6 +/- 4.9 mm Hg in control, 101.2 +/- 19.3 mm Hg in 0.1 microM, and 115.5 +/- 13.3 mm Hg in 1 microM SEA0400, means +/- SE, n = 6, P < 0.05). SEA0400 reduced left ventricular end-diastolic pressure and increased coronary flow after reperfusion. SEA0400 improved the recoveries of cardiac phosphocreatine and ATP after reperfusion, but did not affect pHi. There were significant linear correlations between left ventricular developed pressure and cardiac phosphocreatine (r = 0.79, P < 0.05), and left ventricular developed pressure and ATP (r = 0.80, P < 0.05). However, SEA0400 increased the incidence and duration of reperfusion ventricular arrhythmias. SEA0400 added only after reperfusion also improved both the contractile function and energy metabolism. It is concluded that the selective inhibition of NCX may be effective to preserve high-energy phosphates and to improve cardiac function after reperfusion, but may not be able to prevent fatal arrhythmias.     

Effects of SEA0400, a Na+/Ca2+ exchange inhibitor, on ventricular arrhythmias in the in vivo dogs

SEA0400 (2-[4-[(2,5-difluorophenyl)methoxy]phenoxy]-5-ethoxyaniline), a novel and selective inhibitor of Na+/Ca2+ exchanger, was investigated for its possible antiarrhythmic effects on arrhythmias of Ca2+ overload induced by coronary ligation/reperfusion and by digitalis in the dog. SEA0400 (1.0 mg/kg) did not change the hemodynamics but slightly prolonged the QRS duration (P<0.05). Pre-ischemic administration (10 min before coronary occlusion) of SEA0400 (1.0 mg/kg) and post-ischemic administration (1 min before reperfusion) of SEA0400 (0.3, 1.0 and 3.0 mg/kg) had no effects on the incidence of ventricular fibrillation induced by coronary ligation/reperfusion. On the other hand, SEA0400 (3.0 mg/kg) decreased the arrhythmic ratio in the digitalis arrhythmias (P<0.01). However, atrioventricular block and cardiac standstill were induced in two digitalized dogs. In conclusion, SEA0400 has no significant antiarrhythmic effect on arrhythmias induced by coronary ligation/reperfusion, but has an obvious suppressing effect on tachyarrhythmias induced by digitalis in in vivo canine models.     

Effect of SEA0400, a novel inhibitor of sodium-calcium exchanger, on myocardial ionic currents

The effects of 2-[4-[(2,5-difluorophenyl) methoxy]phenoxy]-5-ethoxyaniline (SEA0400), a newly synthesized Na(+)-Ca(2+) exchanger (NCX) inhibitor, on the NCX current and other membrane currents were examined in isolated guinea-pig ventricular myocytes and compared with those of 2-[2-[4-(4-nitrobenzyloxy) phenyl]ethyl]isothiourea (KB-R7943). SEA0400 concentration-dependently inhibited the NCX current with a 10 fold higher potency than that of KB-R7943; 1 microM SEA0400 and 10 microM KB-R7943 inhibited the NCX current by more than 80%. KB-R7943, at 10 microM, inhibited the sodium current, L-type calcium current, delayed rectifier potassium current and inwardly rectifying potassium current by more than 50%, but SEA0400 (1 microM) had no significant effect on these currents. These results indicate that SEA0400 is a potent and highly selective inhibitor of NCX, and would be a powerful tool for further studies on the role of NCX in the heart and the therapeutic potential of its inhibition.     

Topics on the Na+/Ca2+ exchanger: pharmacological characterization of Na+/Ca2+ exchanger inhibitors

Using the whole-cell voltage clamp, we examined acute effects of various agents on Na(+)/Ca(2+) exchange current (I(NCX)) in guinea-pig cardiac ventricular cells and transfected cells. Among the antiarrhythmic drugs, amiodarone, bepridil, dronedarone, cibenzoline, azimilide, and aprindine inhibited I(NCX) in a concentration-dependent manner. We also investigated the effects on NCX of 2,3-buanedione monoxim (BDM) and selective NCX inhibitors such as KB-R7943, SEA0400, and SN-6. The presence of trypsin in the pipette solution attenuated the inhibitory effects on NCX of amiodarone, bepridil, and BDM, suggesting that these drugs inhibit NCX from the cytosolic side. In contrast, the trypsin-insensitive NCX inhibitors were aprindine, azimilide, dronedarone, cibenzoline, KB-R7943, SEA0400, and SN-6. KB-R7943, SEA0400, and SN-6 suppressed the uni-directional outward I(NCX) more potently than the uni-directional inward I(NCX). The mechanism of this mode-dependency is unknown, but is suggested to be related to intracellular Na(+) concentration.     

Involvement of the Na+/Ca2+ exchanger in ouabain-induced inotropy and arrhythmogenesis in guinea-pig myocardium as revealed by SEA0400

Involvement of the Na+/Ca2+ exchanger in ouabain-induced inotropy and arrhythmogenesis was examined with a specific inhibitor, SEA0400. In right ventricular papillary muscle isolated from guinea-pig ventricle, 1 microM SEA0400, which specifically inhibits the Na+/Ca2+ exchanger by 80%, reduced the ouabain (1 microM)-induced positive inotropy by 40%, but had no effect on the inotropy induced by 100 microM isobutyl methylxantine. SEA0400 significantly inhibited the contracture induced by low Na+ solution. In HEK293 cells expressing the Na+/Ca2+ exchanger, 1 microM ouabain induced an increase in intracellular Ca2+, which was inhibited by SEA0400. The arrhythmic contractions induced by 3 microM ouabain were significantly reduced by SEA0400. These results provide pharmacological evidence that the Na+/Ca2+ exchanger is involved in ouabain-induced inotropy and arrhythmogenesis.     

Topics on the Na+/Ca2+ exchanger: involvement of Na+/Ca2+ exchanger in the vasodilator-induced vasorelaxation

Many kinds of vasodilators induce relaxation of the vascular smooth muscle cells (VSMCs) through the production of cyclic AMP (cAMP) or cyclic GMP (cGMP). The relaxant effects mediated by these second messengers are thought to be mainly due to the decrease in intracellular Ca(2+) concentration ([Ca(2+)](i)), as well as the decrease in Ca(2+) sensitivity of the contractile apparatus of VSMCs. To explain the cAMP- or cGMP-mediated decrease in [Ca(2+)](i), several mechanisms have been proposed, including the inhibition of Ca(2+) influx due to a hyperpolarization, a stimulation of Ca(2+) uptake into the intracellular store, and an increase in Ca(2+) extrusion from VSMCs by stimulation of sarcolemmal Ca(2+)-pump. VSMCs have two major systems for Ca(2+) extrusion, namely, sarcolemmal Ca(2+)-pump and Na(+)/Ca(2+) exchanger (NCX). However, the involvement of NCX in the vasodilator-induced relaxation of VSMCs has not been well established. In this article, the possible involvement of NCX in the vasodilator-induced relaxation of VSMCs will be reviewed.     

SEA0400, a specific Na+/Ca2+ exchange inhibitor, prevents dopaminergic neurotoxicity in an MPTP mouse model of Parkinson's disease

We have recently shown that the Na⁺/Ca²⁺ exchanger (NCX) is involved in nitric oxide (NO)-induced cytotoxicity in cultured astrocytes and neurons. However, there is no in vivo evidence suggesting the role of NCX in neurodegenerative disorders associated with NO. NO is implicated in the pathogenesis of neurodegenerative disorders such as Parkinson’s disease. This study examined the effect of SEA0400, the specific NCX inhibitor, on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic neurotoxicity, a model of Parkinson’s disease, in C57BL/6J mice. MPTP treatment (10 mg/kg, four times at 2-h intervals) decreased dopamine levels in the midbrain and impaired motor coordination, and these effects were counteracted by S-methylthiocitrulline, a selective neuronal NO synthase inhibitor. SEA0400 protected against the dopaminergic neurotoxicity (determined by dopamine levels in the midbrain and striatum, tyrosine hydroxylase immunoreactivity in the substantia nigra and striatum, striatal dopamine release, and motor deficits) in MPTP-treated mice. SEA0400 had no radical-scavenging activity. SEA0400 did not affect MPTP metabolism and MPTP-induced NO production and microglial activation, while it attenuated MPTP-induced increases in extracellular signal-regulated kinase (ERK) phosphorylation and lipid peroxidation product, thiobarbituric acid reactive substance. These findings suggest that SEA0400 protects against MPTP-induced neurotoxicity probably by blocking ERK phosphorylation and lipid peroxidation which are downstream of NCX-mediated Ca²⁺ influx.     

SEA0400, a specific inhibitor of the Na+-Ca2+ exchanger, attenuates sodium nitroprusside-induced apoptosis in cultured rat microglia

1. Using SEA0400, a potent and selective inhibitor of the Na+-Ca2+ exchanger (NCX), we examined whether NCX is involved in nitric oxide (NO)-induced disturbance of endoplasmic reticulum (ER) Ca2+ homeostasis followed by apoptosis in cultured rat microglia. 2. Sodium nitroprusside (SNP), an NO donor, decreased cell viability in a dose- and time-dependent manner with apoptotic cell death in cultured microglia. 3. Treatment with SNP decreased the ER Ca2+ levels as evaluated by measuring the increase in cytosolic Ca2+ level induced by exposing cells to thapsigargin, an irreversible inhibitor of ER Ca2+-ATPase. 4. The treatment with SNP also increased mRNA expression of CHOP and GPR78, makers of ER stress. 5. SEA0400 at 0.3-1.0 microM protected microglia against SNP-induced apoptosis. 6. SEA0400 blocked not only the SNP-induced decrease in ER Ca2+ levels but also SNP-induced increase in CHOP and GRP78 mRNAs. 7. SEA0400 did not affect capacitative Ca2+ entry in the presence and absence of SNP. 8. SNP increased Na+-dependent 45Ca2+ uptake and this increase was blocked by SEA0400. 9. These results suggest that SNP induces apoptosis via the ER stress pathway and SEA0400 attenuates SNP-induced apoptosis via suppression of the ER stress in cultured microglia. Our findings imply that NCX plays a role in ER Ca2+ depletion under pathological conditions.     

Effects of SEA0400 and KB-R7943 on Na+/Ca2+ exchange current and L-type Ca2+ current in canine ventricular cardiomyocytes

SEA0400 and KB-R7943 are compounds synthesised to block transsarcolemmal Na⁺/Ca²⁺ exchange current (I_Na/Ca); however, they Have also been shown to inhibit L-type Ca²⁺ current (I_Ca). The potential value of these compounds depends critically on their relative selectivity for I_Na/Ca over I_Ca. In the present work, therefore, the concentration-dependent effects of SEA0400 and KB-R7943 on I_Na/Ca and I_Ca were studied and compared in canine ventricular cardiomyocytes using the whole-cell configuration of the patch clamp technique. SEA0400 and KB-R7943 decreased I_Na/Ca in a concentration-dependent manner, having EC₅₀ values of 111±43 nM and 3.35±0.82 M, when suppressing inward currents, while the respective EC₅₀ values were estimated at 108±18 nM and 4.74±0.69 M in the case of outward current block. SEA0400 and KB-R7943 also blocked I_Ca, having comparable EC₅₀ values (3.6 M and 3.2 M, respectively). At higher concentrations (10 M) both drugs accelerated inactivation of I_Ca, retarded recovery from inactivation and shifted the voltage dependence of inactivation towards more negative voltages. The voltage dependence of activation was slightly modified by SEA0400, but not by KB-R7943. Based on the relatively good selectivity of submicromolar concentrations of SEA0400—but not KB-R7943—for I_Na/Ca over I_Ca, SEA0400 appears to be a suitable tool to study the role of I_Na/Ca in Ca²⁺ handling in canine cardiac cells. At concentrations higher than 1 M, however, I_Ca is progressively suppressed by the compound.     

Forefront of Na+/Ca2+ exchanger studies: regulation kinetics of Na+/Ca2+ exchangers

Five isoforms of Na+/Ca2+ exchanger have been identified: NCX1, NCX2, NCX3, NCX-SQ1, and CALX. In all of the exchangers, the Na+/Ca2+ exchange current, which was recorded in inside-out membrane patches, was regulated by cytoplasmic Ca2+. However, the mode of regulation is different among the exchangers. NCX1, NCX2, and NCX-SQ1 are positively regulated by cytoplasmic Ca2+, but CALX is negatively regulated. NCX3 apparently has both positive and negative regulation mechanisms. In this review, I briefly summarize the Ca2+ -dependent regulation mechanisms of the exchangers.     

Topics on the Na+/Ca2+ exchanger: responses of Na+/Ca2+ exchanger to interferon-gamma and nitric oxide in cultured microglia

The Na(+)/Ca(2+) exchanger (NCX) plays a role in regulation of intracellular Ca(2+) levels, but little is known about the functional role of NCX in microglia. To clarify the role of NCX in microglia, we studied the responses of NCX to pathological conditions such as interferon-gamma or nitric oxide (NO) exposure. Treatment with interferon-gamma caused a biphasic increase in NCX activity. The delayed increase in NCX activity was accompanied by increases in the mRNA and protein levels. Pharmacological studies show that protein kinase C and tyrosine kinase are involved in the transient and delayed increases in NCX activity, and the extracellular signal-regulated protein kinase is involved in the delayed increase in NCX activity. On the other hand, NO causes apoptotic cell death in cultured microglia. We observed, using the specific NCX inhibitor SEA0400, that NO activates NCX activity and NCX is involved in NO-induced depletion of Ca(2+) in the endoplasmic reticulum (ER), leading to ER stress. These results suggest that NCX is involved in the regulation of Ca(2+) levels in the ER. The responses of NCX to interferon-gamma and NO implies that NCX plays a key role in microglial function.     

ORM-10103, a novel specific inhibitor of the Na+/Ca2+ exchanger,decreases early and delayed afterdepolarizations in the canine heart

BACKGROUND AND PURPOSE

At present there are no small molecule inhibitors that show strong selectivity for the Na⁺/Ca²⁺ exchanger (NCX). Hence, we studied the electrophysiological effects of acute administration of ORM-10103, a new NCX inhibitor, on the NCX and L-type Ca²⁺ currents and on the formation of early and delayed afterdepolarizations.

EXPERIMENTAL APPROACH

Ion 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 RESULTS

ORM-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 Ca²⁺ current or the maximum rate of depolarization (dV/dt_max), indicative of the fast inward Na⁺ current. At 10 μM ORM-10103 did not affect the amplitude or the dV/dt_max of the slow response action potentials recorded from guinea pig papillary muscles, which suggests it had no effect on the L-type Ca²⁺ 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 IMPLICATIONS

ORM-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

This article is commented on by Terracciano and Hancox, pp. 765–767 of this issue. To view this commentary visit http://dx.doi.org/10.1111/bph.12299     

Effects of a selective inhibitor of Na+/Ca2+ exchange, KB-R7943, on reoxygenation-induced injuries in guinea pig papillary muscles

The effects of a novel agent that is reported to selectively block Ca2+ influx by Na+/Ca2+ exchange (NCX), KB-R7943, on the reoxygenation-induced arrhythmias and the recovery of developed tension after reoxygenation, were investigated in guinea pig papillary muscles. KB-R7943 dose-dependently suppressed the contracture tension during low-sodium (21.9 mM) perfusion (23+/-8% of steady-state developed tension at 10 microM vs. 56+/-11% in control; n = 6, p<0.05), but did not change action potential and contractile parameters. During the reoxygenation period after 60-min substrate-free hypoxia, KB-R7943 (10 microM) significantly decreased the incidence of arrhythmias (44 vs. 100% in control; n = 9, p <0.05) and shortened the duration of arrhythmias (16+/-11 vs. 72+/-14 s; p<0.01). KB-R7943 (10 microM) significantly enhanced the recovery of developed tension after reoxygenation (83+/-4 vs. 69+/-3% in control; p<0.05). We conclude that KB-R7943 (10 microM) selectively inhibits the reverse mode of NCX, and that it attenuates reoxygenation-induced arrhythmic activity and prevents contractile dysfunction in guinea pig papillary muscles. These results suggest that Ca2+ influx by NCX may play a key role in reoxygenation injury.     

Pharmacological profile of KR-33028, a highly selective inhibitor of Na+/H+ exchanger

We evaluated the cardioprotective effects of 4-cyano (benzo[b]thiophene-2-carbonyl)guanidine (KR-33028), a recently developed inhibitor of the Na+/H+ exchanger (NHE), on hypoxia-induced H9c2 cell death and on perfused rat hearts subjected to ischemia/reperfusion. KR-33028 inhibited in a concentration-dependent manner the recovery from acidosis induced by an NH4Cl prepulse in PS120 fibroblast cells expressing the human NHE-1 isoform (IC50: 2.59 microM). Treatment with KR-33028 (1-10 microM) significantly decreased hypoxia-induced necrotic cell death and apoptotic cell death in H9c2 cells. KR-33028 significantly inhibited hypoxia-induced increases in cytosolic and mitochondrial Ca2+ level and cytochrome c release, and recovered hypoxia-induced Delta psi(m) reduction. In the perfused rat hearts subjected to 30 min of ischemia and 30 min of reperfusion, KR-33028 (1-10 microM) improved cardiac contractility, decreased lactate dehydrogenase release, and increased content of tissue ATP, creatine phosphate and glycogen in a concentration-dependent manner. In addition, KR-33028 did not produce significant acute or subacute toxicity in the rats at doses tested. Our results suggest that a novel NHE-1 inhibitor KR-33028 possesses potent cardioprotective effects with minimal toxicity and that the effects may be mediated by inhibition of intracellular Ca2+ overload and mitochondrial cell death pathway.     

Forefront of Na+/Ca2+ exchanger studies: role of Na+/Ca2+ exchanger--lessons from knockout mice

We used Na+/Ca2+ exchanger (NCX) knockout mice to evaluate the effects of NCX in cardiac function and the infarct size after ischemia/reperfusion injury. The contractile function in NCX KO mice hearts was significantly better than that in wild type (WT) mouse hearts after ischemia/reperfusion and the infracted size was significantly smaller in NCX KO mice hearts compared with that in WT mice hearts. NCX is critically involved in the development of ischemia/reperfusion-induced myocardial injury, and therefore the inhibition of NCX function may contribute to cardioprotection against ischemia/reperfusion injury.     

Protective effect of KB-R7943, a novel Na+/Ca2+ exchange inhibitor, on ischemic acute renal failure in rats

The effects of KB-R7943 (2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea methanesulfonate), a novel Na+/Ca2+ exchange inhibitor, on ischemic acute renal failure (ARF) in rats were examined. ARF was induced by clamping the left renal pedicle for 45 min followed by reperfusion, 2 weeks after contralateral nephrectomy. Renal function was markedly diminished in ARF rats. Pretreatment with KB-R7943 (10 mg/kg, i.v.) markedly attenuated the ARF-induced renal dysfunction. Histopathological examination of the kidney of ARF rats revealed severe renal damage, which was suppressed by KB-R7943. Activation of the reverse mode of Na+/Ca2+ exchange seems to play an important role in the pathogenesis of ARF. A selective Na+/Ca2+ exchange inhibitor may be useful in cases of ARF.