Protein kinase C and Ca(2+) -calmodulin-dependent protein kinase II mediate the enlarged reverse INCX induced by ouabain-increased late sodium current in rabbit ventricular myocytes.

What is the central question of this study? What are the effects of protein kinase C (PKC) and Ca(2+) -calmodulin-dependent protein kinase II (CaMKII) on late sodium current (INaL ), reverse Na(+) -Ca(2+) exchange current (reverse INCX ) or intracellular Ca(2+) levels changed by ouabain? What is the main finding and its importance? Ouabain, even at low concentrations (0.5-8.0 μm), can increase INaL and reverse INCX , and these effects may contribute to the effect of the glycoside to increase Ca(2+) transients and contractility.

Cardiac late Na⁺ current: proarrhythmic effects, roles in long QT syndromes, and pathological relationship to CaMKII and oxidative stress.

Myocyte sodium channel current that persists throughout the plateau of the cardiac action potential is referred to as late sodium current (I(Na-L)). The magnitude of I(Na-L) is normally small, but can increase significantly in common acute and chronic pathological settings as a result of inherited and/or acquired Na(+) channelopathies that alter channel opening and closing (ie, gating), location (trafficking), or anchoring and interactions with cytoskeletal proteins. An increase in I(Na-L) reduces repolarization reserve in atrial and ventricular myocytes and prolongs the action potential duration and the QT interval.

Intracellular Na+ overload causes oxidation of CaMKII and leads to Ca2+ mishandling in isolated ventricular myocytes.

An increase of late Na(+) current (INaL) in cardiac myocytes can raise the cytosolic Na(+) concentration and is associated with activation of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and alterations of mitochondrial metabolism and Ca(2+) handling by sarcoplasmic reticulum (SR). We tested the hypothesis that augmentation of INaL can increase mitochondrial reactive oxygen species (ROS) production and oxidation of CaMKII, resulting in spontaneous SR Ca(2+) release and increased diastolic Ca(2+) in myocytes. Increases of INaL and/or of the cytosolic Na(+) concentration led to mitochondrial ROS production and oxidation of CaMKII to cause dysregulation of Ca(2+) handling in rabbit cardiac myocytes.

The role of late I Na in development of cardiac arrhythmias.

Late I Na is an integral part of the sodium current, which persists long after the fast-inactivating component. The magnitude of the late I Na is relatively small in all species and in all types of cardiomyocytes as compared with the amplitude of the fast sodium current, but it contributes significantly to the shape and duration of the action potential. This late component had been shown to increase in several acquired or congenital conditions, including hypoxia, oxidative stress, and heart failure, or due to mutations in SCN5A, which encodes the α-subunit of the sodium channel, as well as in channel-interacting proteins, including multiple β subunits and anchoring proteins.

Ranolazine attenuates hypoxia- and hydrogen peroxide-induced increases in sodium channel late openings in ventricular myocytes.

Ranolazine attenuates cardiac arrhythmic activity associated with hypoxia and hydrogen peroxide (H2O2) by inhibition of late sodium current (late INa). The mechanism of ranolazine's action on Na channels was investigated using whole-cell and single-channel recording from guinea pig isolated ventricular myocytes. Hypoxia increased whole-cell late INa from -0.

Larger late sodium current density as well as greater sensitivities to ATX II and ranolazine in rabbit left atrial than left ventricular myocytes.

An increase of cardiac late sodium current (INa.L) is arrhythmogenic in atrial and ventricular tissues, but the densities of INa.L and thus the potential relative contributions of this current to sodium ion (Na(+)) influx and arrhythmogenesis in atria and ventricles are unclear.

Inhibition of the late sodium current slows t-tubule disruption during the progression of hypertensive heart disease in the rat.

The treatment of heart failure (HF) is challenging and morbidity and mortality are high. The goal of this study was to determine if inhibition of the late Na(+) current with ranolazine during early hypertensive heart disease might slow or stop disease progression. Spontaneously hypertensive rats (aged 7 mo) were subjected to echocardiographic study and then fed either control chow (CON) or chow containing 0.

The arrhythmogenic consequences of increasing late INa in the cardiomyocyte.

This review presents the roles of cardiac sodium channel NaV1.5 late current (late INa) in generation of arrhythmic activity. The assumption of the authors is that proper Na(+) channel function is necessary to the maintenance of the transmembrane electrochemical gradient of Na(+) and regulation of cardiac electrical activity.

A novel, potent, and selective inhibitor of cardiac late sodium current suppresses experimental arrhythmias.

Inhibition of cardiac late sodium current (late I(Na)) is a strategy to suppress arrhythmias and sodium-dependent calcium overload associated with myocardial ischemia and heart failure. Current inhibitors of late I(Na) are unselective and can be proarrhythmic. This study introduces GS967 (6-[4-(trifluoromethoxy)phenyl]-3-(trifluoromethyl)-[1,2,4]triazolo[4,3-a]pyridine), a potent and selective inhibitor of late I(Na), and demonstrates its effectiveness to suppress ventricular arrhythmias.

An apoptosis signal-regulating kinase 1 inhibitor reduces cardiomyocyte apoptosis and infarct size in a rat ischemia-reperfusion model.

Purposes: We determined whether a small molecule inhibitor of apoptosis signal-regulating kinase 1 (ASK1-i) could reduce myocardial infarct size in a rat ischemia/reperfusion model.

Methods And Results: Sprague-Dawley rats were randomized to 3 groups: ASK1-i infusion (n = 16), vehicle infusion (n = 16), or ischemic preconditioning (IPC; n = 15). Infusion of ASK1-i (10 mg/kg, iv) or vehicle commenced 45 minutes before myocardial ischemia.

Block of Na+ currents and suppression of action potentials in embryonic rat dorsal root ganglion neurons by ranolazine.

Ranolazine, an anti-anginal drug, reduces neuropathic and inflammatory-induced allodynia in rats. However, the mechanism of ranolazin's anti-allodynic effect is not known. We hypothesized that ranolazine would reduce dorsal root ganglion (DRG) Na(+) current (I(Na)) and neuronal firing by stabilizing Na(+) channels in inactivated states to cause voltage- and frequency-dependent block.

Calmodulin kinase II and protein kinase C mediate the effect of increased intracellular calcium to augment late sodium current in rabbit ventricular myocytes.

An increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) augments late sodium current (I(Na.L)) in cardiomyocytes. This study tests the hypothesis that both Ca(2+)-calmodulin-dependent protein kinase II (CaMKII) and protein kinase C (PKC) mediate the effect of increased [Ca(2+)](i) to increase I(Na.

Structure-activity relationships of 2-amino-3-aroyl-4-[(4-arylpiperazin-1-yl)methyl]thiophenes. Part 2: Probing the influence of diverse substituents at the phenyl of the arylpiperazine moiety on allosteric enhancer activity at the A₁ adenosine receptor.

In a preliminary article, we reported the potent allosteric enhancer activity at the A(1) adenosine receptor of a small series of 2-amino-3-(4-chlorobenzoyl)-4-[4-(aryl)piperazin-1-yl)methyl]thiophene derivatives bearing electron-withdrawing or electron-releasing groups at the para-position of the phenylpiperazine moiety. In the present study, we report the development of the compounds previously studied by modifying both the number and position of substituents on the phenylpiperazine moiety, aimed at establishing a structure-activity relationship identifying additional compounds with improved activity. The nature and the position of substituents on the phenyl ring tethered to the piperazine seemed to exert a fundamental influence on the allosteric enhancer activity, with the 3,4-difluoro 4i, 3-chloro-4-fluoro 4o, and 4-trifluoromethoxy 4ak derivatives being the most active compounds in binding (saturation and competition experiments) and functional cAMP studies.

Selective action of metoprolol to attenuate regadenoson-induced tachycardia in conscious dogs.

Background: Regadenoson is a coronary vasodilator that causes tachycardia via activation of the sympathetic nervous system. We determined whether β(1)-adrenergic blockade can attenuate tachycardia without significantly reducing coronary vasodilation induced by regadenoson.

Methods And Results: Hemodynamics and coronary blood flow (CBF) were measured in conscious dogs.

Nav1.5-dependent persistent Na+ influx activates CaMKII in rat ventricular myocytes and N1325S mice.

Late Na(+) current (I(NaL)) and Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) are both increased in the diseased heart. Recently, CaMKII was found to phosphorylate the Na(+) channel 1.5 (Na(v)1.

Antiadrenergic and hemodynamic effects of ranolazine in conscious dogs.

Effects of ranolazine alone and in the presence of phenylephrine (PE) or isoproterenol (ISO) on hemodynamics, coronary blood flow and heart rate (HR) in the absence and presence of hexamethonium (a ganglionic blocker) were studied in conscious dogs. Ranolazine (0.4, 1.

Late sodium current contributes to the reverse rate-dependent effect of IKr inhibition on ventricular repolarization.

Background: The reverse rate dependence (RRD) of actions of I(Kr)-blocking drugs to increase the action potential duration (APD) and beat-to-beat variability of repolarization (BVR) of APD is proarrhythmic. We determined whether inhibition of endogenous, physiological late Na(+) current (late I(Na)) attenuates the RRD and proarrhythmic effect of I(Kr) inhibition.

Methods And Results: Duration of the monophasic APD (MAPD) was measured from female rabbit hearts paced at cycle lengths from 400 to 2000 milliseconds, and BVR was calculated.

Reducing the late sodium current improves cardiac function during sodium pump inhibition by ouabain.

Inhibition by cardiac glycosides of Na(+), K(+)-ATPase reduces sodium efflux from myocytes and may lead to Na(+) and Ca(2+) overload and detrimental effects on mechanical function, energy metabolism, and electrical activity. We hypothesized that inhibition of sodium persistent inward current (late I(Na)) would reduce ouabain's effect to cause cellular Na(+) loading and its detrimental metabolic (decrease of ATP) and functional (arrhythmias, contracture) effects. Therefore, we determined effects of ouabain on concentrations of intracellular sodium (Na(+)(i)) and high-energy phosphates using (23)Na and (31)P NMR, the amplitude of late I(Na) using the whole-cell patch-clamp technique, and contractility and electrical activity of guinea pig isolated hearts, papillary muscles, and ventricular myocytes in the absence and presence of inhibitors of late I(Na).

Use-dependent block of cardiac late Na(+) current by ranolazine.

Background: Ranolazine is an antianginal drug that inhibits the cardiac late Na+ current (INa). The selectivity of ranolazine to block late INa relative to peak INa at rapid heart rates has not been determined, but is potentially important to drug efficacy and safety.

Objective: This study sought to quantify use-dependent block (UDB) of cardiac peak and late INa by ranolazine.

Sulfonylureas uncouple glucose-dependence for GPR40-mediated enhancement of insulin secretion from INS-1E cells.

Activation of GPR40 is reported to enhance insulin secretion in the presence of glucose. We determined whether sulfonylureas could replace glucose for GPR40-mediated enhancement of insulin secretion and investigated underlying mechanisms using INS-1E cells. GW9508, a specific agonist of GPR40, significantly enhanced insulin secretion in the presence of high concentrations of glucose.

Ranolazine as a cardioplegia additive improves recovery of diastolic function in isolated rat hearts.

Background: Ranolazine (Ran), an antianginal agent, inhibits late Na(+) current. The purpose of this study was to determine whether there was an added benefit of adding Ran to cardioplegia (CP) in a model of global ischemia/reperfusion.

Methods And Results: Isolated rat hearts were Langendorff-perfused and exposed to 40-minute normothermic, cardioplegic global ischemia and 30 minutes of reperfusion.

Ranolazine, an antianginal agent, markedly reduces ventricular arrhythmias induced by ischemia and ischemia-reperfusion.

We tested the effect of the antianginal agent ranolazine on ventricular arrhythmias in an ischemic model using two protocols. In protocol 1, anesthetized rats received either vehicle or ranolazine (10 mg/kg, iv bolus) and were subjected to 5 min of left coronary artery (LCA) occlusion and 5 min of reperfusion with electrocardiogram and blood pressure monitoring. In protocol 2, rats received either vehicle or three doses of ranolazine (iv bolus followed by infusion) and 20 min of LCA occlusion.

A slowly inactivating sodium current contributes to spontaneous diastolic depolarization of atrial myocytes.

Diastolic depolarization (DD) of atrial myocytes can lead to spontaneous action potentials (APs) and, potentially, atrial tachyarrhythmias. This study examined the hypotheses that 1) a slowly inactivating component of the Na(+) current (referred to as late I(Na)) may contribute to DD and initiate AP firing and that 2) blocking late I(Na) will reduce spontaneous and induced firing of APs by atrial myocytes. Guinea pig atrial myocytes without or with DD and spontaneous AP firing were studied using the whole cell patch-clamp technique.

Reduction of repolarization reserve unmasks the proarrhythmic role of endogenous late Na(+) current in the heart.

Reduction of repolarization reserve increases the risk of arrhythmia. We hypothesized that inhibition of K(+) current (I(K)) to decrease repolarization reserve would unmask the proarrhythmic role of endogenous, physiological late Na(+) current (late I(Na)). Monophasic action potentials (MAP) and 12-lead electrocardiogram were recorded from female rabbit isolated hearts.