Comparison of the protective actions of Na+/H+ and Na+/Ca2+ exchange inhibitors in ischemic/reperfused rat hearts

The protective effects of the Na⁺/H⁺ exchange inhibitors amiloride, EIPA (5‐(N‐ethyl‐N‐isopropyl)‐amiloride), and HOE 694 (3‐methylsulfonyl‐4‐(1‐piperidino) benzoyl‐guanidine) and the Na⁺/Ca²⁺ exchange inhibitor, DCB (3,4‐Dichlorobenzamil) on ischemia (30 min) / reperfusion (30 min) injury were studied using Langendorff perfused rat hearts. EIPA and HOE 694 given before ischemia protected the heart during reperfusion from mechanical and metabolic disturbances. A weak protective effect was observed with amiloride, but not with DCB. The cardioprotective efficacies of these compounds correlated with their potencies as Na⁺/H⁺ exchange inhibitors as assessed by the NH₄Cl prepulse method. None of the inhibitors was effective when given at reperfusion. EIPA and HOE 694 decreased myocardial rigidity as assessed by the resting tension (RT) which elevated during reperfusion. EIPA led to a more marked attenuation of RT elevation during reperfusion rather than ischemia, whereas diltiazem, a Ca²⁺ channel blocker, suppressed RT elevation during ischemia but did not cause a further attenuation of RT during reperfusion. Treatment with EIPA as well as diltiazem before ischemia showed a direct negative chronotropic effect. Cardioprotective effects were also observed with diltiazem. These results suggest that Na⁺/H⁺ exchange plays a more important role in ischemia‐reperfusion‐induced myocardial injury than does Na⁺/Ca²⁺ exchange. The cardioprotective effects of EIPA appear to be produced by Ca²⁺ channel blockade during ischemia and by Na⁺/H⁺ exchange inhibition during reperfusion. Drug Dev. Res. 48:160–170, 1999. © 1999 Wiley‐Liss, Inc.     

Restoration of osmotically inhibited twitch force in rat cardiac trabeculae: role of Na+-H+ exchange

1. When rat cardiac muscle is subjected to an increase of osmolality, its peak twitch force is immediately inhibited. Subsequently, over a period of several minutes, twitch force undergoes restoration, the extent of which is determined by the osmolality. The aim of the present study was to determine the factors that contribute to this restorative phenomenon. 2. Trabeculae were isolated from the right ventricles of rat hearts and mounted in an organ bath at 37 degrees C. The osmolality of the bathing solution was increased by 100 mOsmol (to 400 mOsmol) by the addition of various proportions of NaCl and sucrose while recording twitch force production. The role of Na+-H+ exchange in restoring twitch force was examined by use of the specific inhibitor cariporide (HOE 642). The role of Na+-Ca2+ exchange was examined by reducing [Ca2+]o (from 2 mmol/L to 0.5 mmol/L) or by substituting LiCl for NaCl. 3. Cariporide (25 micro mol/L) completely abolished twitch force restoration, thereby implicating a central role for the Na+-H+ exchanger. At constant [Na+]o, the extent of restoration was [Ca2+]o dependent, suggesting an independent contribution by the Na+-Ca2+ exchanger. This suggestion was supported by the finding that Li+, which substitutes for Na+ on the Na+-H+ exchanger, but not on the Na+-Ca2+ exchanger, also reduced the extent of restoration of hyperosmotically inhibited twitch force. 4. We conclude that the immediate inhibition of peak twitch force of rat cardiac muscle by hyperosmotic solutions reflects, in part, elevation of [H+]i, subsequent to reduction of cell volume. Hyperosmotic activation of Na+-H+ exchange then progressively relieves the inhibitory effect of protons on force development. The accompanying increase in [Na+]i in turn enhances Ca2+ influx on the Na+-Ca2+ exchanger, with the result that twitch force undergoes further restoration.     

Inhibitory effect of aprindine on Na+/Ca2+ exchange current in guinea-pig cardiac ventricular myocytes

1. Using the whole-cell voltage clamp technique, the effect of aprindine on Na+/Ca2+ exchange current (I(NCX)) was examined in guinea-pig single cardiac ventricular myocytes and CCL39 fibroblasts expressing a dog cardiac Na+/Ca2+ exchanger (NCX1). 2. I(NCX) was recorded by ramp pulses from the holding potential of -60 mV with the external solution containing 140 mM Na+ and 1 mM Ca2+, and the pipette solution containing 20 mM Na+, 20 mM BAPTA and 13 mM Ca2+ (433 nM free Ca2+). 3. External application of aprindine suppressed I(NCX) in a concentration-dependent manner. The IC50 values of outward (measured at 50 mV) and inward (measured at -100 mV) I(NCX) components were 48.8 and 51.8 microM with Hill coefficients of 1.3 and 1, respectively. 4. Intracellular application of trypsin via the pipette solution did not change the blocking effect of aprindine, suggesting that aprindine does not affect the exchanger from the cytoplasmic side. 5. Aprindine inhibited I(NCX) of a mutant NCX1 with a deletion of amino acids 247 - 671 in the large intracellular domain between the transmembrane segments 5 and 6 in a similar manner to that of the wild-type, suggesting that the site of aprindine inhibition is not in the large intracellular domain of NCX1. 6. A kinetic study indicated that aprindine was cooperatively competitive with KB-R7943, another inhibitor of NCX and that aprindine was a competitive inhibitor with respect to external Ca2+. 7. We conclude that aprindine may modestly inhibit I(NCX) in a therapeutic range of concentrations (around 2.5 approximately 6.9 microM) possibly at an external or intra-membranous site of the exchanger.     

Na+-H+交换及其抑制剂研究进展

Na^ -H^ 交换（NHE）普遍存在于包括人在内的哺乳动物组织细胞膜，对生物有着重要的作用。本文综述了NHE对于生物体内维持细胞恒定的pH值，调节电解质的含量，控制上皮细胞物质的的转运等多种生理作用，介绍了其在心肌缺血中的病理作用，报道了近年来NHE抑制剂的最新研究进展。     

Direct effects of esmolol and landiolol on cardiac function, coronary vasoactivity, and ventricular electrophysiology in guinea-pig hearts

The ultra-short acting, selective β(1)-adrenergic antagonists landiolol and esmolol are widely used perioperatively; however, little is known about their acute direct actions on the heart. The current study utilized the Langendorff perfused heart system to measure changes in cardiac function and hemodynamics in response to each drug. Furthermore, electrophysiological analysis was performed on isolated ventricular myocytes. Direct application of esmolol significantly decreased systolic left ventricular pressure and heart rate at concentrations > 10 μM, while it dose-dependently increased coronary perfusion pressure. Esmolol also shortened the action potential duration (APD) in a concentration-dependent manner, an action maintained even when the delayed rectifier K(+) current or ATP sensitive K(+) current was blocked. Moreover, esmolol inhibited both the inward rectifier K(+) current (I(K1)) and the L-type Ca(2+) current (I(CaL)) and increased the outward current dose-dependently. In contrast, landiolol had minimal cardiac effects. In the Kyoto Model computer simulation, inhibition of either I(K1) or I(CaL) alone failed to shorten the APD; however, an additional increase in the time-independent outward current caused shortening of the APD, equal to that induced by esmolol. In conclusion, esmolol directly inhibits cardiac performance significantly more so than landiolol, an effect revealed to be at least in part mediated by esmolol-induced APD shortening.     

Amiloride derivatives as blockers of Na+/Ca2+ exchange: effects on mechanical and electrical function of guinea-pig myocardium.

The amiloride derivatives, 2',3'-benzobenzamil (BB), 3',4'-dichlorobenzamil (DCB), and 5-(N-4-chlorobenzyl)-2',4'-dimethylbenzamil (CBDB) are known as inhibitors of the Na+/Ca2+ exchange. This kind of drug action was recently suggested to be a new inotropic mechanism. In guinea-pig myocardium, we have studied the inotropic and the accompanying electrophysiological effects of the three compounds in order to assess their selectivity of action. In left atria and in papillary muscle, force of contraction increased with DCB and CBDB (atria only) at a high concentration (5 x 10(-5)-10(-4) mol/l) and after long exposure time, whereas BB produced a negative inotropic effect. In the isolated perfused Langendorff heart, the amiloride derivatives tested decreased spontaneous heart rate and force of contraction and prolonged the duration of contraction. In isolated cardiac myocytes, sodium current, calcium current and the delayed rectifier were reduced by concentrations of BB, DCB and CBDB similar to the IC50 values reported for the inhibition of the Na+/Ca2+ exchange. Our results demonstrate that the amiloride derivatives have multiple sites of action. It is concluded that more specific modulators of the Na+/Ca2+ exchange are required in order to define their contribution to the regulation of contractile activation of the heart.     

Na+/H+ exchange inhibition attenuates left ventricular remodeling and preserves systolic function in pressure-overloaded hearts

Cardiac hypertrophy is a homeostatic response to elevated afterload. Na+/H+ exchanger (NHE) inhibition reduces the hypertrophic response in animal models of left ventricular hypertrophy (LVH) and myocardial infarction. We examined the effect of chronic treatment with cariporide, a selective inhibitor of Na+/H+ exchanger isoform 1 (NHE-1), on left ventricular (LV) systolic and diastolic function under pressure overload conditions. Male CD-1 mice were randomized to receive either a control diet or an identical diet supplemented with 6000 p.p.m. of cariporide. Cardiac pressure overload was induced by thoracic aortic banding. LV dimension and systolic and diastolic function were assessed in sham and banded mice by echocardiography and cardiac catheterization 2 and 5 weeks after surgery. Histological analysis was also performed. After 2 weeks of pressure overload, the vehicle-treated banded mice (Veh-Bd) had enhanced normalized LV weight (about +50%) and normal chamber size and function, whereas cariporide-treated banded mice (Car-Bd) showed a preserved contractility and systolic function despite a marked attenuation of LVH. Diastolic function did not differ significantly among groups. After 5 weeks, the Veh-Bd developed LV chamber enlargement and systolic dysfunction as evidenced by a 16% increase in LV end-diastolic diameter, a 36% decrease in myocardial contractility, and a 26% reduction in percent fractional shortening. In contrast, Car-Bd showed an attenuated increase in LV mass, normal chamber size, and a maintained systolic function. A distinct histological feature was that in banded mice, cariporide attenuated the development of cardiomyocyte hypertrophy but not the attendant myocardial fibrosis. In conclusion, the results of the present study indicate that (i) the hypertrophic response to pressure overload is dependent on NHE-1 activity, and (ii) at the 5-week stage, banding-induced deterioration of LV performance is prevented by NHE-1 inhibition.British Journal of Pharmacology (2004) 141, 526-532. doi:10.1038/sj.bjp.0705631     

Effect of Hoe 694, a novel Na(+)-H+ exchange inhibitor, on intracellular pH regulation in the guinea-pig ventricular myocyte.

1. Hoe 694 (3-methylsulphonyl-4-piperidinobenzoyl, guanidine hydrochloride) is a Na+/H+ exchange (NHE) inhibitor exhibiting cardioprotective properties during ischaemia and reperfusion in animal hearts. We have (i) tested the selectivity of Hoe 694 for NHE over other pHi-regulating mechanisms in the myocardium, and (ii) tested if the functionally important NHE isoform contributing to intracellular pH regulation in heart is NHE-1, as suggested from molecular biology studies of this protein. 2. pHi was recorded by fluorescence microscopy with carboxy SNARF-1, AM-loaded into single ventricular myocytes of guinea-pig. 3. In nominally HCO3-free media, recovery of pHi from an intracellular acid load is mediated by NHE, and was inhibited by Hoe 694, amiloride (an NHE inhibitor) or dimethyl amiloride (DMA, a high affinity NHE inhibitor) with potency values of 2.05, 87.3 and 1.96 microM respectively, giving the potency series: Hoe 694 congruent to DMA > > amiloride. This potency series, and the potency values (corrected for drug competition with extracellular Na+) match those determined previously for cloned NHE-1 expressed in mutant fibroblasts. In the absence of extracellular Na+ (to inhibit NHE), Hoe 694 had no effect on pHi. 4. In 5% CO2/HCO3(-)-buffered solution containing DMA, pHi recovery from acidosis is mediated by Na(+)-HCO3- symport and was unaffected by Hoe 694. The drug also had no effect on pHi recovery from an alkali-load, a process largely mediated by Cl(-)-HCO3- exchange. Finally, the fall of pHi upon adding extracellular Na-lactate is assisted by H(+)-lactate symport, and this too was unaffected by Hoe 694. 5. We conclude (i) Hoe 694 has no detectable inhibitory potency for pH-regulating carriers in heart other than NHE. (ii) native NHE functioning during pHi-regulation in the cardiomyocyte is the NHE-1 isoform. These data strengthen the case for NHE-1 being the receptor for mediating the cardioprotective effects of Hoe 694.     

Direction-independent block of bi-directional Na+/Ca2+ exchange current by KB-R7943 in guinea-pig cardiac myocytes

1. We investigated the inhibitory effect of KB-R7943 on 'bi-directional' Na+/Ca2+ exchange current (iNCX) with the reversal potential of iNCX (ENCX) in the middle of the ramp voltage pulse employed. 2. Bi-directional iNCX was recorded with 'full' ramp pulses given every 10 s from the holding potential of -60 mV over the voltage range between 30 and -150 mV under the ionic conditions of 140 mM [Na]o, 20 mM [Na]i, 1 mM [Ca]o and 433 nM [Ca]i with calculated ENCX at -50 mV. 3. KB-R7943 (0.1 - 100 mirconM) concentration-dependently inhibited the current, which reversed near the calculated ENCX, indicating that the blocked current was iNCX. 4. The inhibition levels were not significantly different between outward and inward iNCX measured at 0 and -120 mV, respectively. IC50 of KB-R7943 was approximately 1 micronM for both directions of iNCX. 5. Under the bi-directional ionic conditions, only an outward or inward iNCX was induced by positive or negative 'half' ramp pulses, respectively, from the holding potential of -60 mV. KB-R7943 inhibited both direction of iNCX and the concentration-inhibition relations were superimposable to the ones obtained by 'full' ramp pulses. 6. These results indicate that KB-R7943 inhibits iNCX direction-independently under bi-directional conditions. This conclusion is different from that of our previous results obtained from iNCX under uni-directional ionic conditions, where KB-R7943 inhibited iNCX direction-dependently. The difference could be attributed to slow dissociation of the drug from the exchanger.     

Preservation of mitochondrial function may contribute to cardioprotective effects of Na+/Ca2+ exchanger inhibitors in ischaemic/reperfused rat hearts

BACKGROUND AND PURPOSE: Na+/Ca2+ exchanger (NCX) inhibitors are known to attenuate myocardial reperfusion injury. However, the exact mechanisms for the cardioprotection remain unclear. The present study was undertaken to examine the mechanism underlying the cardioprotection by NCX inhibitors against ischaemia/reperfusion injury. EXPERIMENTAL APPROACH: Isolated rat hearts were subjected to 35-min ischaemia/60-min reperfusion or 20-min ischaemia/60-min reperfusion. NCX inhibitors (3-30 microM KB-R7943 (KBR) or 0.3-1 microM SEA0400 (SEA)) were given for 5 min prior to ischaemia (pre-ischaemic treatment) or for 10 min after the onset of reperfusion (post-ischaemic treatment). KEY RESULTS: With 35-min ischaemia/60-min reperfusion, pre- or post-ischaemic treatment with KBR or SEA neither enhanced post-ischaemic contractile recovery nor attenuated ischaemia- or reperfusion-induced Na+ accumulation and damage to mitochondrial respiratory function. With the milder model (20-min ischaemia/reperfusion), pre- or post-ischaemic treatment with 10 microM KBR or 1 microM SEA significantly enhanced the post-ischaemic contractile recovery, associated with reductions in reperfusion-induced Ca2+ accumulation, damage to mitochondrial function, and decrease in myocardial high-energy phosphates. Furthermore, Na+ influx to mitochondria in vitro was enhanced by increased concentrations of NaCl. KBR (10 microM) and 1 microM SEA partially decreased the Na+ influx. CONCLUSIONS AND IMPLICATIONS: The NCX inhibitors exerted cardioprotective effects during relatively mild ischaemia. The mechanism may be attributable to prevention of mitochondrial damage, possibly mediated by attenuation of Na+ overload in cardiac mitochondria during ischaemia and/or Ca2+ overload via the reverse mode of NCX during reperfusion.     

Amiloride: relationship between cardiac effects and inhibition of Na+/Ca2+ exchange

The potassium sparing diuretic amiloride at concentrations ranging between 0.1-0.8 mM inhibited the Na+/Ca2+ exchange in sarcolemmal vesicles isolated from beef heart. The rate of exchange activity was 50% reduced by 0.35 mM amiloride. In spontaneously beating atria isolated from normal and reserpinized guinea-pigs, amiloride produced a concentration-dependent positive inotropic effect and negative chronotropic effect (EC50 = 0.7 mM). Amiloride protected spontaneously beating atria and left atria driven at 1 Hz from digitalis cardiotoxicity assessed in terms of a raised end-diastolic tension. It is suggested that the positive inotropic effect, negative chronotropic effect of amiloride and heart protection against digitalis toxicity are related to the observed inhibition of sarcolemmal Na+/Ca2+ exchange activity.     

A possible action of nicardipine on the cardiac sarcolemmal Na+-Ca2+ exchange

The effects of nicardipine on sodium-calcium exchange activity of cardiac sarcolemma-enriched vesicles isolated from the rat heart were examined. Sodium-loaded, sarcolemma-enriched vesicles, when exposed to a medium containing 40 microM CaCl2, exhibited about 5 nmoles Ca2+/mg protein of the maximal calcium uptake; the initial rate was 21 nmoles Ca2+/mg protein/min. The calcium uptake was dependent on the extravesicular concentration of calcium ion. Nicardipine at concentrations of 0.1 to 10 microM depressed the rate of calcium uptake activity by 60-90%. The isolated membrane vesicles preloaded with Ca2+ showed a calcium efflux activity, when exposed to a medium containing sodium ion. The rate of calcium efflux was 2.5 nmoles Ca2+/mg protein/min, when measured in a medium containing 6.5 mM NaCl. The efflux rate was facilitated with increased concentrations of sodium ion in the medium. About 75% of the preloaded calcium in the vesicles was released within 3 min of incubation. The rate of calcium efflux was stimulated in the presence of 0.1 to 10 microM nicardipine (2.5- to 4-fold increase). The present results suggest a possible action of nicardipine on the sodium-calcium exchange mechanism at cardiac sarcolemmal sites.     

Absence of increased electroneutral Na+-H+ exchange in renal cortical brush-border membranes from hyperthyroid rats

The fluorescence quenching of acridine orange was used to compare Na+-H+ exchange and ion conductances in renal cortical brush-border membrane vesicles (BBMV) isolated from euthyroid and hyperthyroid rats. In BBMV from euthyroid animals, Na+-H+ exchange was entirely electroneutral. In BBMV from hyperthyroid rats, the total rates of Na+-H+ exchange were about 30% higher than in BBMV from euthyroid animals. However, the electroneutral exchange in these membranes was similar to that in BBMV from euthyroid rats; the observed increase in exchange was due to electrically coupled Na+ and H+ movements through conductive pathways in the membranes. Ion conductances in isolated BBMV were tested with outwardly directed K+ gradients in the presence of carbonyl cyanide m-chlorophenylhydrazone (K+ conductance) or valinomycin (H+ conductance). The K+ conductance was negligible and similar in BBMV from both groups of rats. A significant H+ conductance was present in both kinds of membrane preparations and was by 37% higher in BBMV from hyperthyroid animals. Therefore, our experiments failed to demonstrate an increased electroneutral Na+-H+ exchange in BBMV from hyperthyroid rats. Instead, a finding of a significant electrically BBMV from hyperthyroid rats. Instead, a finding of a significant electrically coupled Na+-H+ antiport in the presence of increased H+ conductance in BBMV from hyperthyroid rats indicates that these membranes may also have increased Na+ conductance.     

Inhibitory effect of amiodarone on Na(+)/Ca(2+) exchange current in guinea-pig cardiac myocytes

The effect of amiodarone on Na(+)/Ca(2+) exchange current (I(NCX)) was examined in single guinea-pig ventricular myocytes using the whole-cell voltage clamp technique. I(NCX) was recorded by ramp pulses from the holding potential of -60 mV in the presence of 140 mM Na(+) and 2 mM Ca(2+) in the external solution, and 20 mM Na(+) and 398 nM free Ca(2+) (19 mM Ca(2+) and 30 mM BAPTA) in the internal solution. External application of amiodarone suppressed I(NCX) in a concentration-dependent manner. The IC(50) value was 3.3 microM with a Hill coefficient of 1. Intracellular application of trypsin via the micropipette attenuated the blocking effect of amiodarone, suggesting that amiodarone affects the cytoplasmic side of the molecule. This inhibitory effect of amiodarone on the Na(+)/Ca(2+) exchanger may contribute to the cardioprotective action of the drug.     

In vitro and in vivo pharmacology of a structurally novel Na+-H+ exchange inhibitor, T-162559

1. We investigated the inhibitory effects of a non-acylguanidine Na(+)-H(+) exchange (NHE) inhibitor, T-162559 ((5E,7S)-[7-(5-fluoro-2-methylphenyl)-4-methyl-7,8-dihydro-5(6H)-quinolinylideneamino] guanidine dimethanesulphonate), on NHE-1, and its cardioprotective effect against ischaemia and reperfusion injury in rats and rabbits. 2. T-162559 inhibited human platelet NHE-1 in a concentration-dependent manner, with an IC(50) value of 13+/-3 nmol l(-1), making it 16 and three times more potent than cariporide IC(50): 209+/-75 nmol l(-1), P<0.01) and eniporide (IC(50): 40+/-11 nmol l(-1), P=0.066), respectively. T-162559 also inhibited rat NHE-1 with an IC(50) value of 14+/-2 nmol l(-1), which was five and three times lower than that of cariporide (IC(50): 75+/-7 nmol l(-1), P<0.01) and eniporide (IC(50): 44+/-2 nmol l(-1), P<0.01), respectively. 3. T-162559 inhibited, in a concentration-dependent manner, the reduction in cardiac contractility, progression of cardiac contracture, and increase in lactate dehydrogenase release after global ischaemia and reperfusion in perfused rat hearts. The inhibitory effects of T-162559 were observed at a lower concentration range (10 - 100 nmol l(-1)) than with cariporide and eniporide. T-162559 did not alter basal cardiac contractility or coronary flow after reperfusion, suggesting that it exerts direct cardioprotective effects on the heart. 4. Intravenous administration of T-162559 (0.03 and 0.1 mg kg(-1)) significantly inhibited the progression of myocardial infarction induced by left coronary artery occlusion and reperfusion in rabbits; the infarct size normalized by area at risk was 74+/-6% in the vehicle group, and 47+/-5% and 51+/-7% in the T-162559-0.03 mg kg(-1) and T-162559-0.1 mg kg(-1) groups (both P<0.05), respectively. 5. These results indicate that the new structural NHE-1 inhibitor T-162559 is more potent than cariporide and eniporide and possesses a cardioprotective effect against ischaemia and reperfusion injury in rat and rabbit models.     

Inhibitory effects of diprafenone stereoenantiomers on cardiac Na+ channels

The potency of (-)- and (+)-diprafenone to depress the Vmax of Na+-dependent action potentials and to block single cardiac Na+ channels was analyzed in microelectrode experiments with guinea pig papillary muscles and in patch clamp experiments with DPI-modified Na+ channels using neonatal cardiocytes. Within 20-30 min, both optical enantiomers caused a Vmax depression which occurred predominantly as a phasic blockade at a low dosage (10 mumol/l). (-)- and (+)-diprafenone were equally effective in evoking a tonic and phasic depression of Vmax. Exposing the cytoplasmic side of inside-out patches to 10 mumol/l of (-)- or (+)-diprafenone evoked a flicker block of DPI-modified Na+ channels within 1-2 s. Kinetic analysis of the latter revealed a KD value for the blocking action of 6.3 X 10(-5) mol for the (-) enantiomer and 7.1 X 10(-5) mol for the (+) enantiomer. Nevertheless, larger association and dissociation rate constants were obtained with (+)-diprafenone than with (-)-diprafenone. This indicates that there are stereoselective reaction kinetics in blocking open modified Na+ channels.     

Protective effects of poly (ADP-ribose) synthase inhibitors on digoxin-induced cardiotoxicity in guinea-pig isolated hearts.

Reactive oxygen species, generated and released during digoxin-induced cardiotoxicity, can produce an activation of poly (ADP-ribose) synthase (PARS). Our objective was to examine the effects of PARS inhibitors, 3-aminobenzamide (3-AB ) and nicotinamide, on digoxin-induced arrhythmias in guinea-pig isolated hearts. 3-AB (0.1-0.3 mM) and nicotinamide (0.3 mM) were added to the perfusion solution starting 10 min before digoxin infusion (8 microg x ml (-1)min (-1)reaching the heart) and maintained throughout the experiments. Electrocardiograms and coronary perfusion pressure were recorded continuously, and digoxin-induced arrhythmias were determined. Nicotinamide markedly inhibited ventricular tachycardia (VT) incidence (from 100%, n= 7, to 29%, n= 7), and abolished ventricular fibrillation (VF) incidence. 3-AB (0.1 mM, n= 9) significantly decreased VT incidence from 100% ( n= 7) to 22% ( n= 9) and VF incidence from 86% ( n= 7) to 11% ( n= 9). Both nicotinamide and 3-AB (0.1 mM) markedly decreased number of ventricular ectopic beats (VEBs) and arrhythmia score. 3-AB at 0.3 mM ( n= 8) appeared to decrease the VT (to 63%) and VF incidence (to 38%), but these reductions did not reach statistically significance levels. Moreover, 3-AB at high concentration (0.3 mM) did not significantly modify the number of VEBs and arrhythmia score. There were no significant changes in coronary perfusion pressure, heart rate or pressure rate index measured at certain time points throughout the experiment in all groups. Our results suggest that PARS activation plays a role in the digitalis-induced cardiotoxicity in guinea-pig isolated hearts.     

Inhibition of Na+-H+ exchange by cariporide reduces inflammation and heart failure in rabbits with myocardial infarction

The aim of this study was to assess the effects of the Na+-H+ exchange inhibitor cariporide on left ventricular (LV) morphology and function as well as inflammation in rabbits with heart failure. Rabbits with myocardial infarction (MI) and sham controls were randomized to receive either standard chow or chow supplemented with cariporide for 9 weeks. LV morphology was determined by echocardiography. LV systolic and diastolic function was assessed under load-dependent and -independent conditions by analysis of LV pressure-volume loops using piezo-electric crystals. Plasma concentrations of C-reactive protein and aldosterone were measured. Rabbits with MI developed LV dilatation that was reduced by cariporide. Systolic and diastolic LV function was impaired in rabbits with MI when compared to sham, as indicated by a decreased dP/dtmax (MI: 3537 +/- 718 mmHg s(-1), sham: 5839 +/- 247 mmHg s(-1), P < 0.05), the load-independent preload recruitable stroke work (PRSW)(MI: 22 +/-7 mmHg, sham: 81 +/- 23 mmHg, P < 0.05) and a reduction in the time constant of relaxation tau (tau) (MI: 27+/-1 ms, sham: 17+/-1 ms, P < 0.05), and significantly improved by cariporide (dP/dtmax: 4586 +/- 374 mmHg s(-1), PRSW: 67 +/- 18 mmHg, tau: 20 +/- 2 ms; P < 0.05 vs MI/control). Induction of MI was associated with an increase in aldosterone and CRP, indicating activation of the neurohormonal and the inflammatory system that were largely reduced by cariporide. Cariporide improves LV morphology and function post MI and suppresses inflammation and neurohormonal activation in congestive heart failure (CHF). Na+-H+ exchange inhibition may represent a new pharmaceutical approach for the treatment of CHF.