Rapid electrophysiological changes leading to arrhythmias in the aerobic rat heart. Photosensitization studies with rose bengal-derived reactive oxygen intermediates

The objective of this study was to determine whether reactive oxygen intermediates (e.g., singlet oxygen and the superoxide radical) can rapidly induce electrophysiological disturbances leading to the genesis of arrhythmias, even in the absence of ischemia and reperfusion. Rat hearts (n = 6 per group) were perfused aerobically at 37 degrees C for 10 minutes without rose bengal and for 5 minutes with rose bengal (250 nmol/l), during which time no changes in coronary flow or heart rate were observed. Hearts were then uniformly illuminated for 20 minutes with green light (530-590 nm) from 200 fiber optic cables. With light and without rose bengal, or vice versa, all hearts remained stable. However, in the illuminated rose bengal group, electrophysiological changes (inversion of the terminal portion of the T wave and an increase in Q-T interval) were observed within 11.8 +/- 2.1 seconds (i.e., less than 60 beats). All hearts exhibited ventricular premature beats (within 2.2 +/- 0.7 minutes) and ventricular tachycardia (within 2.8 +/- 0.7 minutes) before the occurrence of complete atrioventricular block (within 5.5 +/- 0.9 minutes). During the illumination period, coronary flow progressively fell in the rose bengal-perfused hearts from 11.6 +/- 0.5 ml/min to 2.0 +/- 0.4 ml/min (p less than 0.05 when compared with any control group). When a similar progressive reduction in coronary flow was mimicked (with or without rose bengal), no arrhythmias occurred.(ABSTRACT TRUNCATED AT 250 WORDS)     

Exacerbation of reperfusion arrhythmias by sudden oxidant stress

A burst of free oxygen radical production has been demonstrated during the early moments of reperfusion, coincident with the onset of reperfusion arrhythmias, which can be attenuated by antioxidants. We have investigated whether a sudden burst of oxidant stress, superimposed on that occurring during reperfusion, can exacerbate reperfusion arrhythmias. Rat hearts (n = 12/group) were subjected to 12 minutes of aerobic perfusion; during the last 2 minutes, rose bengal (1 mumol/l) was added to the perfusion fluid. Then, regional ischemia was induced, and rose bengal-free perfusion was restored. After 5 minutes of ischemia, reperfusion was initiated for 5 minutes, and during the first 30 seconds of reperfusion, hearts were uniformly illuminated (8,500 lux) with green light (530-590 nm). The photoactivation of rose bengal trapped in the tissue, producing singlet oxygen and superoxide, resulted in an exacerbation of reperfusion arrhythmias. Thus, 92% of hearts developed ventricular premature beats, 83% ventricular tachycardia, and 33% ventricular fibrillation. In contrast, hearts with regional ischemia and reperfusion in the absence of rose bengal and/or illumination did not develop ventricular fibrillation; only one heart exhibited ventricular tachycardia, and the incidence of ventricular premature beats was lower (42-50%). Furthermore, the burst of oxidant stress shortened the time to onset of ventricular premature beats from 21.7 +/- 5.6 to 9.9 +/- 2.1 seconds. Additional studies revealed that rose bengal photoactivation without reperfusion was less arrhythmogenic compared with the combination of reperfusion plus photoactivation. These results demonstrate that a sudden burst of oxidant stress during the early moments of reperfusion can exacerbate the vulnerability to reperfusion arrhythmias.     

Species differences in vulnerability to injury by oxidant stress: a possible link with calcium handling?

STUDY OBJECTIVE--The aim was to exploit species- and age dependent differences in calcium handling to assess the role of calcium as a mediator of oxidant stress induced injury in the mammalian heart. DESIGN--Hearts from immature and mature rats and rabbits were perfused aerobically with buffer containing rose bengal which was photoactivated by illumination--a process that generates singlet oxygen and superoxide. This oxidant stress rapidly leads to electrocardiographic abnormalities, ultrastructural injury, and a redistribution of calcium. EXPERIMENTAL MATERIAL--Isolated perfused hearts from mature (60-90 d old) and immature (4-6 d old) rats, and mature (60-90 d old) and immature (7-10 d old) rabbits. MEASUREMENTS AND MAIN RESULTS--In hearts (n = 6 per group) from mature rats, aerobic perfusion and photoactivation for 5 min with buffer containing rose bengal (250 and 1000 nmol.litre-1) had no significant effect upon heart rate (until the onset of arrhythmias) but did result in a dose dependent transient increase in coronary flow. ECG abnormalities appeared within less than 30 s and these deteriorated to ventricular premature beats (VPB) and ventricular tachycardia (VT) in most hearts. By contrast, in identical studies with comparable sized hearts from young rabbits, ECG changes and arrhythmias occurred later, and the incidence of VT and the mean number of VPB were lower. Although arrhythmias were less severe in rabbit hearts, photoactivation of rose bengal caused both coronary flow and heart rate to fall in a dose dependent manner. Increasing the concentration of rose bengal to a value (2500 nmol.litre-1), which would be highly toxic in the rat heart, increased the severity of injury in the rabbit heart, the nature of which differed from that in the rat heart. To assess whether developmental state, as opposed to species, was a factor determining the differences in vulnerability to injury, hearts from immature rats and adult rabbits were perfused with various concentrations of rose bengal (250-2500 nmol.litre-1) with the intensity of illumination (1400-6600 Lux) adjusted to account for the size of the heart. Under these conditions rabbit hearts were found to be less vulnerable to injury and arrhythmias than rat hearts, and hearts from immature rats were found to be less vulnerable than those from adult rats. CONCLUSIONS--The results of this and other studies suggest that species and developmental differences in calcium handling (sarcolemmal v sarcoplasmic reticulum control) might explain the differences in vulnerability to arrhythmias.     

Singlet oxygen and myocardial injury: ultrastructural, cytochemical and electrocardiographic consequences of photoactivation of rose bengal

Photoactivation of rose bengal leads to the generation of reactive oxygen intermediates (predominantly singlet oxygen with some superoxide anion) which are potentially injurious to biological systems. Isolated rat hearts were perfused aerobically at 37 degrees C with bicarbonate buffer for 10 min without rose bengal and for 10 min with rose bengal (500 nM). During the last 5 min of perfusion with rose bengal, hearts were globally illuminated (5500 lux) with light (530 to 590 nm) and electrocardiographic changes were detected within 2.7 +/- 0.3 s (approximately 15 beats) of the onset of illumination. All hearts developed ventricular premature beats, ventricular tachycardia and complete atrioventricular block after 20.2 +/- 6.6, 68.0 +/- 29.7 and 184.3 +/- 20.9 s, respectively. Photoactivation by rose bengal also resulted in severe ultrastructural damage including intracellular clarifications, swelling of mitochondria with disruption and clumping of cristae and the development of contraction band necrosis. Extensive degranulation of mast cells was also observed. These changes were most evident in myocytes adjacent to large epicardial blood vessels. Cytochemical studies demonstrated that there was a loss of the calcium which is normally localized at the inner sarcolemmal surface, and the appearance of intramitochondrial calcium precipitates. In control hearts (no illumination and/or no rose bengal), arrhythmias did not develop and tissue morphology and calcium distribution remained normal. In additional studies, rose bengal-perfused hearts were illuminated regionally for 10 min over an area (approximately 6 mm2) of the left ventricle. Extensive tissue injury and calcium overload developed in the area of maximum illumination.(ABSTRACT TRUNCATED AT 250 WORDS)     

The genesis of arrhythmias during myocardial ischemia. Dissociation between changes in cyclic adenosine monophosphate and electrical instability in the rat

It has been proposed that increases in tissue cyclic adenosine monophosphate during ischemia may be responsible for the induction of arrhythmias that occur during the early minutes of ischemia. We have tested this hypothesis using the isolated perfused rat heart with coronary artery occlusion for 30 minutes. In control hearts, after a transient small rise, cyclic adenosine monophosphate content remained close to its preischemic value (3.0 +/- 0.1 nM/g dry weight) throughout the period of occlusion. Eight percent (1/12) of the hearts fibrillated. Ninety-two percent (11/12) of the hearts exhibited ventricular tachycardia, and the mean total number of premature ventricular complexes was 528 +/- 121. Inclusion of epinephrine (1.0 microM) in the perfusion fluid elevated cyclic adenosine monophosphate prior to coronary occlusion (to 10.7 +/- 0.6 nM/g dry weight) and also throughout the ischemic period. It also increased arrhythmias such that 83% (20/24) of hearts fibrillated, 100% exhibited ventricular tachycardia, and the mean number of premature ventricular complexes increased to 747 +/- 86. Inclusion of forskolin (0.2 microM), which stimulates adenyl cyclase independently of the beta-receptor, increased cyclic adenosine monophosphate content to a greater extent than epinephrine, to 14.1 +/- 0.9 nM/g dry weight before the onset of ischemia and to 8.2 +/- 0.4 nM/g dry weight after 30 minutes of ischemia. Despite the large increase in cyclic adenosine monophosphate, there was no increase in rhythm disturbances which were less than those seen in controls.(ABSTRACT TRUNCATED AT 250 WORDS)     

Membrane potential fluctuations and transient inward currents induced by reactive oxygen intermediates in isolated rabbit ventricular cells

The cellular basis of reactive oxygen intermediate-induced arrhythmias was investigated in isolated rabbit ventricular cells using the whole-cell voltage- and current-clamp techniques. Singlet oxygen and superoxide were generated by the photoactivation of rose bengal. Single ventricular cells exposed to rose bengal (10-100 nM) exhibited spontaneous membrane potential fluctuations at plateau potentials and at the level of the resting membrane potential. The voltage fluctuations induced in the resting potential occasionally triggered repetitive action potential discharges. At the resting membrane potential, the magnitude and dominant frequency of the voltage fluctuations were 1-3 mV and 1.5 Hz, respectively. At plateau potentials, the amplitude of the voltage fluctuations was about 2-5 mV, and the dominant oscillatory frequency was 2.6 Hz. In voltage-clamp experiments, transient inward currents were induced on repolarization after a depolarizing clamp step. Oscillatory currents also occurred occasionally during clamp steps to positive potentials. The peak frequencies of transient inward currents recorded at -20 and -70 mV were approximately 3.7 and 2.3 Hz, respectively, indicating that these currents may underlie the arrhythmogenic membrane potential fluctuations observed in current-clamp experiments. The rose bengal-induced transient inward currents were shown to be dependent on the magnitude and duration of the preceding voltage step. Studies of the voltage dependence of transient inward currents showed that these currents remained inward even at positive potentials (+30 mV), and replacement of extracellular sodium with lithium decreased transient inward current to approximately 10% of its initial value. Thus, the major component of oxidant stress-induced inward current appears to be electrogenic Na-Ca exchange. This oscillatory transient inward current may be responsible for the arrhythmias induced in isolated hearts exposed to reactive oxygen intermediates, and since oxidant stress has been implicated in reperfusion injury, it is possible that similar oscillatory currents may underlie reperfusion-induced arrhythmias.     

Effect of preconditioning ischemia on reperfusion arrhythmias after coronary artery occlusion and reperfusion in the rat

Severe arrhythmias occur predictably on reperfusion after 5 minutes of coronary occlusion in the rat. There is little data available on whether ischemic preconditioning (PC) of hearts can reduce the incidence of such arrhythmias. The effect of PC (three cycles of 2 minutes of coronary occlusion and 5 minutes of reperfusion) on development of arrhythmias after a subsequent 5-minute coronary artery occlusion and reperfusion was studied. Rats (n = 16 each group) underwent 5-minute occlusion and reperfusion alone or preceded by PC; arrhythmias were monitored during ischemia and for 10 minutes of reperfusion, and biopsies were taken for creatine phosphate and adenosine triphosphate in ischemic and nonischemic zones of the left ventricle. PC reduced the incidence of ventricular tachycardia (VT) during occlusion (81% control versus 13% PC, p less than 0.001). On subsequent reperfusion, ventricular fibrillation (VF) developed in zero PC animals versus 13 (81%) of controls (p less than 0.001), and irreversible VF in zero of PC versus seven (44%) of controls (p = 0.007). VT occurred in four (25%) of PC versus all (100%) of controls (p less than 0.001). PC reduced mean duration of VT plus VF from 320 +/- 54 to 5 +/- 1 seconds (p less than 0.001) and delayed arrhythmia onset from 8 +/- 2 to 85 +/- 35 seconds after reperfusion. There was no difference in creatine phosphate levels in the ischemic zone at the end of reperfusion in PC animals compared with controls without irreversible VF (16.2 +/- 4.1 versus 15.5 +/- 3.9 nmol/mg protein, p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)     

Photoactivation of porphyrins: studies of reactive oxygen intermediates and arrhythmogenesis in the aerobic rat heart

STUDY OBJECTIVE--In situ production of reactive oxygen intermediates (singlet oxygen and superoxide) during the photoactivation of rose bengal can induce arrhythmias in the aerobically perfused rat heart. The present study was undertaken (1) to assess whether these effects occur with other photosensitizers; (2) to identify the injurious intermediates; (3) to probe the site of action of these phenomena. DESIGN - The study involved the use of meso-tetra-(4-sulphonatophenyl)-porphine (TPPS), a porphyrin which, in contrast to rose bengal, promotes the production of singlet oxygen alone when illuminated. After 10 min of TPPS free perfusion, rat hearts (n = 6 per group) were perfused aerobically with TPPS (1, 5, 10 or 50 mumol.litre-1) for 25 min; during the last 20 min, the hearts were illuminated (3600 lux). In additional studies, TPPS (50 mumol.litre-1) was washed out before illumination. EXPERIMENTAL MATERIAL--Hearts from 30 male Wistar rats, weighing 220-280 g, were excised and perfused retrogradely. MEASUREMENTS AND MAIN RESULTS--Cardiac function was unaffected with TPPS alone. Upon illumination, electrocardiographic changes (increase in QT interval and/or T wave changes) and arrhythmias developed in a dose dependent manner. At the highest dose, electrocardiographic changes occurred within 7.0(SEM 0.4) s; all hearts exhibited ventricular premature beats and complete atrioventricular block; 67% developed ventricular tachycardia and 17% ventricular fibrillation. During illumination, hearts also exhibited a dose and time dependent decrease in coronary flow. In additional studies, despite the absence of TPPS in the perfusate, all hearts exhibited complete atrioventricular block, 67% developed ventricular premature beats and 33% ventricular tachycardia; none exhibited ventricular fibrillation. CONCLUSIONS--The results suggest that singlet oxygen, as opposed to superoxide, is responsible for the injury which occurs at tissue surfaces to which photosensitizer is bound.     

Singlet oxygen interaction with Ca(2+)-ATPase of cardiac sarcoplasmic reticulum.

We investigated the role of singlet oxygen (generated from photoactivation of rose bengal) on the calcium transport and Ca(2+)-ATPase activity of cardiac sarcoplasmic reticulum (SR). Isolated cardiac SR exposed to rose bengal (10 nM) irradiated at 560 nm resulted in significant inhibition of Ca2+ uptake (from 2.27 +/- 0.05 to 0.62 +/- 0.05 mumol Ca2+/mg.min [mean +/- SEM], p less than 0.01) and Ca(2+)-ATPase activity (from 2.08 +/- 0.05 to 0.28 +/- 0.04 mumol Pi/min.mg [mean +/- SEM], p less than 0.01). The inhibition of calcium uptake and Ca(2+)-ATPase activity by rose bengal-derived activated oxygen (singlet oxygen) was dependent on the duration of exposure and intensity of light. Singlet oxygen scavengers ascorbic acid and histidine significantly protected SR Ca(2+)-ATPase against rose bengal-derived activated oxygen species, but superoxide dismutase and catalase did not attenuate the inhibition. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of SR exposed to photoactivated rose bengal for up to 14 minutes demonstrated complete loss of the Ca(2+)-ATPase monomer band, which was significantly protected by histidine. The addition of dithiothreitol (5 mM) had a slight protective effect, showing that new disulfide bond formation was not a major cause of aggregation. The results were also confirmed by high-performance liquid chromatography of the SR exposed to irradiated rose bengal. Irradiation of rose bengal also caused an 18% loss of total sulfhydryl groups of SR. On the other hand, superoxide radical (generated from xanthine oxidase action on xanthine) and hydroxyl radical (in the presence of Fe(3+)-EDTA or 0.5 mM H2O2 plus Fe(2+)-EDTA) as well as H2O2 (0.25-12 mM) were without any effect on the 97,000-d Ca(2+)-ATPase band of SR. Generation of radical species (superoxide and hydroxyl radical) from rose bengal was studied by electron paramagnetic resonance spectroscopy using the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). The results showed that irradiation of rose bengal formed a 1:2:2:1 quartet, characteristic of the DMPO-OH adduct, which was scavenged by ethanol but not by superoxide dismutase, catalase, or histidine. No radical species could be detected from irradiated rose bengal or irradiated DMPO under the assay conditions used. Peroxy adducts of DMPO might be produced but would be observed only at very low temperatures. Similarly, we could not detect any measurable.O2- anion from irradiation of rose bengal as indicated by either cytochrome c reduction at 550 nm or nitro blue tetrazolium reduction at 560 nm. These results show that SR is damaged most likely by singlet oxygen derived from rose bengal.(ABSTRACT TRUNCATED AT 400 WORDS)     

Functional and electrophysiological effects of oxidant stress on isolated ventricular muscle: a role for oscillatory calcium release from sarcoplasmic reticulum in arrhythmogenesis?

STUDY OBJECTIVE--The aim was to investigate the cellular basis of oxidant stress induced arrhythmias by studying the influence of oxidant stress on the contractile and electrophysiological function of isolated cardiac muscle. DESIGN--Oxidant stress was induced by the photoactivation of rose bengal added to the solution superfusing isolated ventricular muscles from a number of species. Measurements of contractile and electrophysiological function were made under control conditions, during exposure to oxidant stress, and under a number of experimental conditions. EXPERIMENTAL MATERIAL--Isolated superfused papillary muscles or trabeculae from rat, rabbit, or frog hearts were used in all studies. MEASUREMENTS AND MAIN RESULTS--The contractile response to oxidant stress was assessed by measuring isometric developed tension and resting tension throughout the experiment, and the electrophysiological response was assessed by recording action potentials using conventional 3 M KCl filled intracellular electrodes. Oxidant stress induced a transient positive inotropy, after-contractions, and eventually contracture. Associated with these contractile changes were prolongation of the action potential, early afterdepolarisations, oscillations in resting membrane potential, and automaticity. These effects were concentration and species dependent and the oscillations in both tension and membrane potential were abolished by inhibition of calcium release from the sarcoplasmic reticulum with caffeine. CONCLUSIONS--The contractile and electrophysiological effects of rose bengal induced oxidant stress are consistent with a cellular calcium overload. The observation that the oscillations in tension and membrane potential were abolished by caffeine and that these effects were species dependent (rat greater than rabbit greater than frog) suggests a role for oscillatory sarcoplasmic reticulum calcium release in these effects. The oscillations in membrane potential and the automaticity induced by rose bengal are likely to underlie the arrhythmias observed in isolated hearts exposed to oxidant stress that have previously been described.     

Role of endogenous arginine vasopressin in potentiating corticotropin-releasing hormone-stimulated corticotropin secretion in man

Exogenously administered vasopressin (VP) augments ACTH secretion stimulated by CRH. This study was performed to elucidate the role of endogenous VP in potentiating CRH-induced ACTH secretion in man. Synthetic human CRH (100 micrograms) was injected iv into seven normal men after they had been water loaded (20 mL/kg; 60 and 30 min before CRH injection; WL-CRH test) and water deprived (water restriction for 18 h before CRH injection; WD-CRH test). Blood samples were obtained before and 5, 15, 30, 60, 90, and 120 min after CRH injection at 0900 h for determination of plasma ACTH, cortisol, arginine vasopressin (AVP), CRH, and catecholamine levels and osmolality. Urine was obtained immediately before and 120 min after CRH injection for determination of osmolality. The mean plasma AVP levels were significantly higher during the WD-CRH test [1.8 +/- 0.4 (+/- SE) to 1.9 +/- 0.4 pmol/L] than during the WL-CRH test (0.6 +/- 0.1 to 0.9 +/- 0.1 pmol/L). The mean plasma ACTH and cortisol levels rose significantly from basal (4.5 +/- 0.6 pmol/L and 320 +/- 20 nmol/L, respectively) to peak values of 14.0 +/- 2.1 pmol/L at 30 min and 700 +/- 50 nmol/L at 60 min, respectively, during the WD-CRH test. During the WL-CRH test, mean basal plasma ACTH and cortisol levels were 3.5 +/- 0.7 pmol/L and 420 +/- 50 nmol/L, respectively, and reached peak values of 7.7 +/- 1.1 pmol/L at 60 min and 550 +/- 40 nmol/L at 30 min, respectively. Both the mean peak levels and integrated ACTH and cortisol responses were significantly higher during the WD-CRH than during the WL-CRH test. There was no significant difference between the plasma CRH and catecholamine concentrations in both tests. These results suggest that endogenous AVP potentiates CRH-stimulated ACTH secretion and, thus, plays a physiologically significant role in regulating CRH-stimulated ACTH and cortisol secretion in man.     

Reperfusion-induced arrhythmias. A role for washout of extracellular protons?

Rapid washout of extracellular H+ accumulated during preceding ischemia (i.e., the abrupt restoration of extracellular pH) has been implicated as an arrhythmogenic factor during reperfusion. Therefore, we hypothesized that by limiting the rate at which extracellular pH was restored during early reperfusion it should be possible to protect against reperfusion-induced arrhythmias. To test this, we used isolated rat hearts (n = 12 per group) and a novel dual coronary perfusion cannula that permitted the induction of regional ischemia (10 minutes) and the selective reperfusion (8 minutes) of the ischemic zone with modified solutions. We examined the antiarrhythmic efficacy of 1) acidic (pH 6.6) reperfusion with stepwise restoration of extracellular pH to 7.4 (stepped pH) and 2) transient (2-minute) acidic (pH 7.1, 6.8, 6.6, or 6.4) reperfusion with subsequent abrupt restoration of extracellular pH to 7.4. Hearts in two contemporary control groups were reperfused with solution at pH 7.4 throughout. In all groups, 100% of hearts exhibited ventricular tachycardia (VT) on reperfusion. VT degenerated into ventricular fibrillation (VF) in 100% of hearts in the control group but in only 42% of hearts in the stepped-pH group (p < 0.05). In the groups subjected to transient acidic reperfusion, there was a pH-dependent prolongation of VT cycle length (measured at 15 seconds of reperfusion), which was 47.1 +/- 3.9, 51.1 +/- 5.5, 56.0 +/- 1.9, 60.4 +/- 2.8 (p < 0.05), and 68.8 +/- 5.0 (p < 0.05) msec in the pH 7.4 (control), 7.1, 6.8, 6.6, and 6.4 groups, respectively. In these groups, VT degenerated into VF in 92%, 92%, 83%, 42% (p < 0.05), and 33% (p < 0.05) of hearts, respectively. In conclusion, limiting the rate at which extracellular pH is restored during early reperfusion does not affect the rapid induction of VT but inhibits the degeneration of VT into VF and promotes spontaneous reversion to normal sinus rhythm. This is consistent with a major arrhythmogenic role, during uncontrolled reperfusion, for the rapid washout of extracellular H+.     

Droperidol lengthens cardiac repolarization due to block of the rapid component of the delayed rectifier potassium current

INTRODUCTION: Torsades de pointes have been observed during treatment with droperidol, a butyrophenone neuroleptic agent. Our objectives were (1) to characterize the effects of droperidol on cardiac repolarization and (2) to evaluate effects of droperidol on a major time-dependent outward potassium current involved in cardiac repolarization (I(K)r). METHODS AND RESULTS: Isolated, buffer-perfused guinea pig hearts (n = 32) were stimulated at different pacing cycle lengths (150 to 250 msec) and exposed to droperidol in concentrations ranging from 10 to 300 nmol/L. Droperidol increased monophasic action potential duration measured at 90% repolarization (MAPD90) in a concentration-dependent manner by 9.8+/-2.3 msec (7.3%+/-0.7%) at 10 nmol/L but by 32.7+/-3.6 msec (25.7%+/-2.2%) at 300 nmol/L (250-msec cycle length). Increase in MAPD90 also was reverse frequency dependent. As noted previously, droperidol 300 nmol/L increased MAPD90 by 32.7+/-3.6 msec (25.7%+/-2.2%) at a pacing cycle length of 250 msec but by only 14.1+/-1.3 msec (13.6%+/-2.3%) at a pacing cycle length of 150 msec. Patch clamp experiments performed in isolated guinea pig ventricular myocytes demonstrated that droperidol decreases the time-dependent outward K+ current elicited by short depolarizations (250 msec; I(K)250) in a concentration-dependent manner. Estimated IC50 for I(K)250, which mostly underlies I(K)r, was 28 nmol/L. Finally, HERG K+ current elicited in HEK293 cells expressing high levels of HERG protein was decreased 50% by droperidol 32.2 nmol/L. CONCLUSION: Potent block of I(K)r by droperidol is likely to underlie QT prolongation observed in patients treated at therapeutic plasma concentrations (10 to 400 nmol/L) of the drug.     

Predictors of rhythm disturbances and subsequent morbidity after the Fontan operation

The electrocardiographic, hemodynamic and surgical data of 30 patients who underwent a Fontan operation between 1977 and 1986 were retrospectively reviewed to identify the incidence and predictors of immediate and late postoperative arrhythmias and associated morbidity in long-term survivors. Of 4 patients who died less than 1 year after operation (mortality 13%), 1 death was related to an arrhythmia. Three patients were not in sinus rhythm before operation and were excluded from the statistical analysis that examined predictors of arrhythmias. The remaining 23 long-term survivors have been followed 6.3 +/- 2.6 years (mean +/- standard deviation) since surgery and all remain in New York Heart Association functional class I or II. Ten patients (43%) developed immediate postoperative arrhythmias (less than or equal to 30 days) whereas 11 (48%) had late arrhythmias. With up to 10.7 years of follow-up, the proportion of patients free from late arrhythmias continues to decline. Arrhythmias included bradyarrhythmias, atrial tachyarrhythmias, the tachy-brady syndrome and supraventricular ectopic activity. Immediate postoperative arrhythmias predicted late arrhythmias (p = 0.022). The preoperative electrocardiogram was the only variable useful in predicting both immediate and late postoperative arrhythmias. A more negative P-wave deflection in lead V1 (-2.4 +/- 0.7 vs -1.4 +/- 1.2 mV, p = 0.02) predicted patients with immediate postoperative arrhythmias, whereas both greater P-wave duration and a more negative deflection in this lead predicted late arrhythmias (103 +/- 14 vs 83 +/- 20 ms, p = 0.01, and -2.5 +/- 0.8 vs -1.3 +/- 1.0 mV, p = 0.005, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Ryanodine and caffeine prevent ventricular arrhythmias during acute myocardial ischemia and reperfusion in rat heart

This study investigates the possible role of oscillatory release of calcium from sarcoplasmic reticulum in the genesis of ventricular arrhythmias during acute myocardial ischemia and reperfusion in isolated rat hearts. We used ryanodine and caffeine, which are known to modulate the oscillatory release of calcium from sarcoplasmic reticulum. During 30 minutes of left main coronary artery ligation, all 13 control hearts developed ventricular premature beats (number of beats, 225 +/- 51) and ventricular tachycardia (duration, 123 +/- 21 seconds); five hearts developed ventricular fibrillation. In a separate series of experiments, reperfusion after 15 minutes of coronary artery ligation caused ventricular fibrillation to occur within 15 seconds in all 12 hearts. Ryanodine (10(-9) to 10(-7) M) abolished ventricular arrhythmias during coronary artery ligation and prevented reperfusion ventricular fibrillation. Ryanodine (10(-9), 10(-8), and 10(-7) M) caused 15%, 23%, and 74% decreases in the maximal rate of rise of left ventricular pressure development and 20%, 32%, and 85% decreases in the maximal rate of fall of left ventricular pressure development, respectively, prior to coronary artery ligation. During acute myocardial ischemia, ryanodine 10(-9) M maintained and 10(-8) M impaired left ventricular function; 10(-7) M caused left ventricular failure. Coronary perfusion rate did not increase during ischemia. Antiarrhythmic activity occurred independent of preservation of high energy phosphates, reduction in tissue lactate, or tissue cyclic adenosine monophosphate in the ischemic myocardium. Caffeine 10(2) M decreased the incidence of ventricular arrhythmias during ischemia and upon reperfusion; protection occurred coincident with development of diastolic contracture. Caffeine increased ischemic tissue cyclic adenosine monophosphate content and worsened tissue energy status.(ABSTRACT TRUNCATED AT 250 WORDS)     

Training depletes muscle glutathione in patients with chronic obstructive pulmonary disease and low body mass index

BACKGROUND: A physiological increase in muscle glutathione after training is not seen in patients with chronic obstructive pulmonary disease (COPD), indicating abnormal peripheral muscle adaptations to exercise. OBJECTIVE: We hypothesized that oxidative stress is primarily associated with low body mass index (BMI). METHODS: Eleven patients with preserved BMI (BMI(N): 28.2 +/- 1.2 kg.m(-2)), 9 patients with low BMI (BMI(L): 19.7 +/- 0.60 kg.m(-2)) and 5 age-matched controls (26.5 +/- 0.9 kg.m(-2)) were studied before and after 8 weeks of high-intensity endurance training. Reduced glutathione (GSH) and gamma-glutamyl cysteine synthase heavy-subunit chain mRNA expression (gammaGCS-HS mRNA) were measured in the vastus lateralis. RESULTS: After training, exercise capacity increased (DeltaVO(2)PEAK, 13 +/- 5.2%; 10 +/- 5.6% and 15 +/- 4.3% in BMI(L), BMI(N) and controls, respectively; p < 0.05 each). GSH levels decreased in BMI(L) (from 5.2 +/- 0.7 to 3.7 +/- 0.8 nmol/mg protein, DeltaGSH -1.5 +/- 0.7 nmol/mg protein, p < 0.05); no changes were seen in BMI(N) (from 5.4 +/- 0.7 to 6.7 +/- 0.9 nmol/mg protein, DeltaGSH 1.3 +/- 0.9 nmol/mg protein), whereas GSH markedly increased in controls (from 4.6 +/- 1 to 8.7 +/- 0.4 nmol/mg protein, DeltaGSH 4.1 +/- 1 nmol/mg protein, p < 0.01). DeltaGSH in BMI(L) was different from DeltaGSH in BMI(N) and controls (p < 0.05, each). Consistent changes were observed in gammaGCS-HS mRNA expression. CONCLUSIONS: GSH depletion after training in BMI(L) may suggest that oxidative stress plays a key role in muscle wasting in COPD patients.     

Extravascular transfer of fluids and proteins induced by endothelin in the binephrectomized rat]

To test the possibility that endothelin affects extracellular fluid partition between plasma and interstitium, we compared the effects of endothelin and vehicule in euvolemic binephrectomized anesthetized rats by measuring changes in hematocrit and plasma protein concentration. Forty-five minutes infusion of endothelin (25 ng/kg/min) induced a progressive increase in blood pressure by 1.7 +/- 1.3, 6.8 +/- 1.5 and 12.1 +/- 2.1% at 15, 30 and 45 min respectively from a basal value of 99 +/- 5 mmHg. Hematocrit increased by 8.0 +/- 0.6% (p less than 0.001) after 45 min of infusion, while the vehicle had no significant effect (+ 1.7 +/- 0.7%). The same increase in hematocrit was observed in binephrectomized and splenectomized rats. The calculated loss of plasma volume during endothelin infusion was 13.1 +/- 0.9% as compared to 2.1 +/- 1.2% in rats receiving the vehicle. Plasma protein concentration increased by only 4.2 +/- 0.6% suggesting an extravasation of proteins. To document and localize an alteration in vascular leak of proteins induced by endothelin, albumin-bound Evans Blue (EB) extravasation was measured spectrophotometrically in different tissues after extraction by formamide. Endothelin increased vascular permeation of EB-albumin in skeletal and cardiac muscle, intestine and mesentery. No change was observed in brain, liver, spleen as compared to rats receiving the vehicle. In addition, endothelin infusion elicits a three fold increase of the plasma immunoreactive atrial natriuretic peptide (ir-ANP) concentration (from 196 +/- 50 to 722 +/- 203 pg/ml; p less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)     

Physiological increments in plasma homocysteine induce vascular endothelial dysfunction in normal human subjects

We hypothesized that physiological increments in plasma homocysteine after low-dose oral methionine or dietary animal protein induce vascular endothelial dysfunction and that there is a graded, inverse relationship between homocysteine concentration and endothelial function. We studied 18 healthy volunteers aged 18 to 59 years. Brachial artery flow-mediated and glyceryltrinitrate-induced dilatation were measured after 1) oral L-methionine (10, 25, and 100 mg/kg), 2) dietary animal protein (lean chicken 551+/-30 g, comprising 3.2+/-0.2 g methionine), and 3) methionine-free amino acid mix (100 mg/kg). Methionine (10, 25, and 100 mg/kg) induced a dose-related increase in homocysteine (9.4+/-1.3 to 12.2+/-2.1, 17. 6+/-2.6, and 26.1+/-4.2 micromol/L, respectively; P<0.001) and a reduction in flow-mediated dilatation (4.1+/-0.8 to 2.1+/-0.8, 0. 3+/-0.8, and -0.7+/-0.8%, respectively; P<0.001) at 4 hours. Compared with usual meal, animal protein increased plasma homocysteine (9.6+/-0.8 to 11.2+/-0.9 micromol/L, P=0.005) and reduced flow-mediated dilatation (4.5+/-0.7% to 0.9+/-0.6%, P=0.003). Methionine-free amino acid mix did not induce any changes. Glyceryltrinitrate-induced dilatation was unchanged throughout. In this study, small physiological increments in plasma homocysteine after low-dose methionine and dietary animal protein induced vascular endothelial dysfunction. We propose that protein intake-induced increments in plasma homocysteine may have deleterious effects on vascular function and contribute to the development and progression of atherosclerosis.     

Electrophysiological effects of dofetilide in an in vitro model of "border zone" between normal and ischemic/reperfused myocardium

BACKGROUND: To evaluate both class III activity and antiarrhythmic action of dofetilide at the level of the "border zone," we investigated its electrophysiological effects on guinea pig ventricular strips submitted partly to normoxia (normal zone, NZ) and partly to simulated severe ischemia, then reperfusion (altered zone, AZ). METHODS AND RESULTS: Because of the differential class III effects of dofetilide in normal and ischemic regions, the dispersion of the action potential duration at 90% repolarization (APD(90)) between NZ and AZ was reduced by 5 nmol/L of drug during early ischemia (at 10 minutes, APD(90) NZ/APD(90) AZ was 1.68+/-0.22 versus 2.82+/-0.17 in control, P<0.05), whereas 50 nmol/L dofetilide worsened it during late ischemia (at 30 minutes, APD(90) NZ/APD(90) AZ was 4.62+/-0.76 versus 2.57+/-0.21 in control, P<0.05). Concomitantly, dofetilide at 5, 10, and 50 nmol/L abolished the early extrastimulus (ES)-induced arrhythmias, and at 10 and 50 nmol/L, it significantly enhanced the incidence of late spontaneous repetitive responses (in 86% and 75% of preparations treated with 10 and 50 nmol/L, respectively, versus 25% in control, P<0.05). During reperfusion, dofetilide at 5, 10, and 50 nmol/L exhibited concentration-dependent class III effects, as it did in the NZ, and did not modify the incidence of spontaneous arrhythmias. CONCLUSIONS: Dofetilide 5 nmol/L decreased APD(90) dispersion between NZ and AZ and reduced the early ES-induced arrhythmias. However, dofetilide 50 nmol/L increased APD(90) dispersion, and at 10 and 50 nmol/L, it increased the late spontaneous arrhythmias.     

Use of transtelephonic electrocardiographic monitoring in children with suspected arrhythmias.

Arrhythmias in children can produce various symptoms and their assessment often is difficult with usual methods. Transtelephonic electrocardiographic monitoring was used in 136 symptomatic patients (palpitations [112], syncope [six], chest pain [18]) for a mean duration of 86 +/- 65 days; mean age was 11.1 +/- 4.8 years and 62% were female. Of 398 recordings sent (mean 2.9 per patient) 32 revealed significant arrhythmias (8%). Of the 67 patients reporting symptoms during the recording period, only 24 had documented arrhythmias - 23 supraventricular tachycardia and one junctional tachycardia. The negative predictive value is 100%, compared with a low positive predictive value of 36%; sensitivity and specificity are, respectively, 100 and 62%. Of the 24 patients with documented arrhythmias, 54% were treated versus 13% of those with normal recordings (P < 0.01). At the end of the follow-up (mean duration 1.6 +/- 1.2 years), 63% of the patients with negative recordings had not complained of further symptoms versus 22% of those with documented arrhythmias (P = 0.001). Transtelephonic electrocardiographic monitoring is an important tool for documenting infrequent arrhythmias in children and even more for reassuring the patient and his or her family in the absence of significant arrhythmias.