Université de Montpellier
MEDECINE
2rev -ABSTRACT Extracellular purines and pyrimidines have major effects on cardiac rhythm and contraction. ATP/UTP are released during various physiopathological conditions such as ischemia and, despite degradation by ectonucleotidases,... more
2rev -ABSTRACT Extracellular purines and pyrimidines have major effects on cardiac rhythm and contraction. ATP/UTP are released during various physiopathological conditions such as ischemia and, despite degradation by ectonucleotidases, their interstitial concentrations can markedly increase, a fact that is clearly associated with arrhythmia. In the present whole-cell patch-clamp analysis on ventricular cardiomyocytes isolated from various mammalian species, ATP and UTP elicited a sustained, non-selective cationic current, I ATP .
Arrhythmias following cardiac stress are a key predictor of death in healthy population. Carbon monoxide (CO) is a ubiquitous pollutant promoting oxidative stress and associated with hospitalization for cardiovascular disease and cardiac... more
Arrhythmias following cardiac stress are a key predictor of death in healthy population. Carbon monoxide (CO) is a ubiquitous pollutant promoting oxidative stress and associated with hospitalization for cardiovascular disease and cardiac mortality. We investigated the effect of chronic CO exposure on the occurrence of arrhythmic events after a cardiac stress test and the possible involvement of related oxidative stress. Wistar rats exposed chronically (4 weeks) to sustained urban CO pollution presented more arrhythmic events than controls during recovery after cardiac challenge with isoprenaline in vivo. Sudden death occurred in 22% of CO-exposed rats versus 0% for controls. Malondialdehyde (MDA), an end-product of lipid peroxidation, was increased in left ventricular tissue of CO-exposed rats. Cardiomyocytes isolated from CO-exposed rats showed higher reactive oxygen species (ROS) production (measured with MitoSox Red dye), higher diastolic Ca 2? resulting from SR calcium leak and an higher occurrence of irregular Ca 2? transients (measured with Indo-1) in comparison to control cells after a high pacing sequence. Acute treatment with a ROS scavenger (N-acetylcysteine, 20 mmol/L, 1 h) prevented this sequence of alterations and decreased the number of arrhythmic cells following high pacing. Chronic CO exposure promotes oxidative stress that alters Ca 2? homeostasis (through RYR2 and SERCA defects) and thereby mediates the triggering of ventricular arrhythmia after cardiac stress that can lead to sudden death.
- by Jérémy Fauconnier and +2
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- Basic Cardiology
We recently showed that disruption of localization of PP2A phosphatase activity to the ryanodine receptor (RyR2) complex by overexpression of the musclespecific microRNA, miR-1, stimulates excitation-contraction coupling and results in... more
We recently showed that disruption of localization of PP2A phosphatase activity to the ryanodine receptor (RyR2) complex by overexpression of the musclespecific microRNA, miR-1, stimulates excitation-contraction coupling and results in increased arrhythmogenic potential in cardiac myocytes. In the present study, we examined the role of PKA and CAMKII as mediators of the effects miR-1 on Ca signaling and arrhythmogenesis using cellular electrophysiology and Ca imaging complemented with quantitative measurements of RyR2 phosphorylation at PKA site S-2808, and at CAMKII site S-2814. Adenovirally-mediated 2-fold overexpression of miR-1 resulted in 10-fold increase in arrhythmogenic potential measured as a frequency of spontaneous Ca waves and DADs in myocytes exposed to 100 nM isoproterenol (ISO). Quantitative imminoblotting using site-directed phosphospecific-antibodies showed that RyR2 phosphorylation in miR-1 overexpressing cells was low at S-2808 under basal conditions. Exposure of myocytes to ISO maximized phosphorylation at S-2808. Phosphorylation at S-2814 under basal conditions was maximal and did not further increase in the presence of ISO. Additionally, ISO increased SERCa-mediated SR Ca uptake and SR Ca load through phosphorylation of phospholamban (PLB). To define which of these factors (increased CaSR content or increased RyR2 PKA phosphorylation) mediated the increased arrhythmogenic potential we infected myocytes with viral constructs of a dominant-negative PLB mutant that accelerates SERCa-mediated SR Ca uptake by displacing endogenous PLB from SERCa. Myocytes coexpressing miR-1 and dnPLB did not exhibit enhanced predisposition to Ca-dependent arrhythmia in the presence of ISO despite maximal SR Ca load. Importantly treatment of cells with either PKA or CAMK inhibitors completely abolished increased arrhythmogenic activity. We conclude that neither CAMKII nor PKA phosphorylation alone is sufficient to produce the changes in RyR2 activity that underlies the arrhythmogenic disturbances caused by miR-1 overexpression. Duchenne muscular dystrophy (DMD) affects one in 3500 newborn males and usually leads to death from respiratory or cardiac failure by age 30. Interestingly, the severity of cardiomyopathy is not proportional to the severity of skeletal muscle disorder. Among DMD patients, the cardiac phenotype varies with age from no discernable cardiac left ventricular enlargement or dysfunction to early onset of dilated cardiomyopathy (DCM) with heart failure. The incidence of DCM in DMD patients has been estimated to be 25% by 6 years of age, 59% at 10 years of age and~100% in adults. DMD patients often exhibit electrocardiographic abnormalities and frequent premature ventricular contractions. As the cardiomyopathy progresses, ventricular arrhythmias (VA) increase, often leading to sudden death. Most of the electrical and functional abnormalities have been attributed to cardiac fibrosis. However, electrical abnormalities may occur in the absence of overt cardiac histopathology and ECG changes are similar in patients with DMD regardless of presence of DCM. Here we show that structural and functional remodeling of the cardiac sarcoplasmic reticulum (SR) Ca2þ release channel/ryanodine receptor (RyR2) occurs in the mdx mouse model of DMD. RyR2 from mdx hearts were S-nitrosylated and depleted of calstabin2 (FKBP12.6) resulting in "leaky" RyR2 channels and diastolic SR Ca2þ leak. Inhibiting the depletion of calstabin2 from the RyR2 complex with the calcium channel stabilizer, S107 ("rycal"), inhibited the SR Ca2þ leak, restored normal Ca2þ transients, inhibited isoproterenol induced aberrant depolarizations in isolated cardiomyocytes and prevented arrhythmias in vivo. Thus, diastolic SR Ca2þ leak via RyR2 due to S-nitrosylation of the channel and calstabin2 depletion from the channel complex likely triggers cardiac arrhythmias. Prevention of the RyR2-mediated diastolic SR Ca2þ leak may provide a novel cardiac therapeutic approach in DMD. The hypothesis that Na current (INa) can induce release of Ca from the sarcoplasmic reticulum (SR) by activating reverse Na-Ca exchange (NCX) has been debated since 1990. We tested this hypothesis with epi-fluorescence imaging of adult rabbit ventricular myocytes loaded with the Ca indicator fluo-4. Ca release was triggered with an action potential clamp with and without an initial voltage ramp from À80 to À40 mV, for a duration of 1.5s. We confirmed that this protocol selectively blocked INa without altering Ca influx through L-type Ca channels (LCCs) and SR Ca load. With 0 mM Na in the pipette (to reduce intracellular Na), inactivating INa reduced SR Ca release flux by 27%54% (n=9). With 5 mM Na in the pipette, the Ca release upon inactivation of INa was reduced by 33%55% (n=4). We suggest that increased activation of reverse NCX by increased intracellular Na concentration mainly produced by INa explains these findings. These conclusions are in agreement with studies on normal and NCX knockout mice, which show that INa affects SR Ca release only in normal, but not in NCX knockout mice. In similar experiments, we applied 100 nM TTX to selectively block brain isoforms of Na channels. In the presence of TTX, the SR Ca release flux was reduced by 35%53% (n=6). This effect of INa on Ca release can be explained by early reverse NCX, activated by TTX sensitive INa, which could prime the dyadic cleft with Ca. Furthermore, the results can be explained if INa activation of NCX, and subsequent priming of the dyadic cleft with Ca, increases the coupling fidelity between LCCs and ryanodine receptors within a couplon. Thus the presence of INa increases the likelihood that couplons are activated.
- by Jérémy Fauconnier and +1
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- Biophysical Chemistry
Myocardial ischemic disease is the major cause of death worldwide. After myocardial infarction, reperfusion of infracted heart has been an important objective of strategies to improve outcomes. However, cardiac ischemia/reperfusion (I/R)... more
Myocardial ischemic disease is the major cause of death worldwide. After myocardial infarction, reperfusion of infracted heart has been an important objective of strategies to improve outcomes. However, cardiac ischemia/reperfusion (I/R) is characterized by inflammation, arrhythmias, cardiomyocyte damage, and, at the cellular level, disturbance in Ca 2+ and redox homeostasis. In this study, we sought to determine how acute inflammatory response contributes to reperfusion injury and Ca 2+ homeostasis disturbance after acute ischemia. Using a rat model of I/R, we show that circulating levels of TNF-α and cardiac caspase-8 activity were increased within 6 h of reperfusion, leading to myocardial nitric oxide and mitochondrial ROS production. At 1 and 15 d after reperfusion, caspase-8 activation resulted in S-nitrosylation of the RyR2 and depletion of calstabin2 from the RyR2 complex, resulting in diastolic sarcoplasmic reticulum (SR) Ca 2+ leak. Pharmacological inhibition of caspase-8 before reperfusion with Q-LETD-OPh or prevention of calstabin2 depletion from the RyR2 complex with the Ca 2+ channel stabilizer S107 ("rycal") inhibited the SR Ca 2+ leak, reduced ventricular arrhythmias, infarct size, and left ventricular remodeling after 15 d of reperfusion. TNF-αinduced caspase-8 activation leads to leaky RyR2 channels that contribute to myocardial remodeling after I/R. Thus, early prevention of SR Ca 2+ leak trough normalization of RyR2 function is cardioprotective.
- by Jérémy Fauconnier and +1
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Patients with Duchenne muscular dystrophy (DMD) have a progressive dilated cardiomyopathy associated with fatal cardiac arrhythmias. Electrical and functional abnormalities have been attributed to cardiac fibrosis; however, electrical... more
Patients with Duchenne muscular dystrophy (DMD) have a progressive dilated cardiomyopathy associated with fatal cardiac arrhythmias. Electrical and functional abnormalities have been attributed to cardiac fibrosis; however, electrical abnormalities may occur in the absence of overt cardiac histopathology. Here we show that structural and functional remodeling of the cardiac sarcoplasmic reticulum (SR) Ca 2+ release channel/ryanodine receptor (RyR2) occurs in the mdx mouse model of DMD. RyR2 from mdx hearts were S-nitrosylated and depleted of calstabin2 (FKBP12.6), resulting in "leaky" RyR2 channels and a diastolic SR Ca 2+ leak. Inhibiting the depletion of calstabin2 from the RyR2 complex with the Ca 2+ channel stabilizer S107 ("rycal") inhibited the SR Ca 2+ leak, inhibited aberrant depolarization in isolated cardiomyocytes, and prevented arrhythmias in vivo. This suggests that diastolic SR Ca 2+ leak via RyR2 due to S-nitrosylation of the channel and calstabin2 depletion from the channel complex likely triggers cardiac arrhythmias. Normalization of the RyR2-mediated diastolic SR Ca 2+ leak prevents fatal sudden cardiac arrhythmias in DMD. calcium | excitation-contraction coupling | heart | sudden cardiac death | myopathy
- by Jérémy Fauconnier and +1
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- Sarcoplasmic reticulum
Sonic hedgehog (SHH) is a conserved protein involved in embryonic tissue patterning and development. SHH signaling has been reported as a cardio-protective pathway via muscle repair-associated angiogenesis. The goal of this study was to... more
Sonic hedgehog (SHH) is a conserved protein involved in embryonic tissue patterning and development. SHH signaling has been reported as a cardio-protective pathway via muscle repair-associated angiogenesis. The goal of this study was to investigate the role of SHH signaling pathway in the adult myocardium in physiological situation and after ischemia-reperfusion. We show in a rat model of ischemia-reperfusion that stimulation of SHH pathway, either by a recombinant peptide or shed membranes microparticles harboring SHH ligand, prior to reperfusion reduces both infarct size and subsequent arrhythmias by preventing ventricular repolarization abnormalities. We further demonstrate in healthy animals a reduction of QTc interval mediated by NO/cGMP pathway leading to the shortening of ventricular cardiomyocytes action potential duration due to the activation of an inward rectifying potassium current sharing pharmacological and electrophysiological properties with ATP-dependent potassium current. Besides its effect on both angiogenesis and endothelial dysfunction we demonstrate here a novel cardio-protective effect of SHH acting directly on the cardiomyocytes. This emphasizes the pleotropic effect of SHH pathway as a potential cardiac therapeutic target. OPEN SUBJECT AREAS: ISCHAEMIA CELL SIGNALLING MEDICAL RESEARCH
- by Jérémy Fauconnier and +2
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- cyclic GMP
We investigated the inward rectifier potassium current (I(K1)), which can be blocked by intracellular Ca(2+), in heart failure (HF). We used the whole-cell patch-clamp technique to record I(K1) from single rat ventricular myocytes in... more
We investigated the inward rectifier potassium current (I(K1)), which can be blocked by intracellular Ca(2+), in heart failure (HF). We used the whole-cell patch-clamp technique to record I(K1) from single rat ventricular myocytes in voltage-clamp conditions. Fluorescence measurements of diastolic Ca(2+) were performed with Indo-1 AM. HF was examined 8 weeks after myocardial infarction (coronary artery ligation). I(K1) was reduced and diastolic Ca(2+) was increased in HF cells. The reduction of I(K1) was attenuated when EGTA was elevated from 0.5 to 10 mM in the patch pipette and prevented with high BAPTA (20 mM). Ryanodine (100 nM) and FK506 (10 microM), both of which promote spontaneous SR Ca(2+) release from ryanodine receptor (RyR2) during diastole, reproduced the effect of HF on I(K1) in normal cells but had no effect in HF cells. The effects of ryanodine and FK506 were not additive and were prevented by BAPTA. Rapamycin (10 microM), which removes FKBP binding proteins from RyR...
During heart failure (HF), the left ventricle (LV) releases B-type natriuretic peptide (BNP), possibly contributing to adverse cardiovascular events including ventricular arrhythmias (VAs) and LV remodelling. We investigated the cardiac... more
During heart failure (HF), the left ventricle (LV) releases B-type natriuretic peptide (BNP), possibly contributing to adverse cardiovascular events including ventricular arrhythmias (VAs) and LV remodelling. We investigated the cardiac effects of chronic BNP elevation in healthy mice and compared the results with a model of HF after myocardial infarction (PMI mice). Healthy mice were exposed to circulating BNP levels (BNP-Sham) similar to those measured in PMI mice. Telemetric surface electrocardiograms showed that in contrast with fibrotic PMI mice, electrical conduction was not affected in BNP-Sham mice. VAs were observed in both BNP-Sham and PMI but not in Sham mice. Analysis of heart rate variability indicated that chronic BNP infusion increased cardiac sympathetic tone. At the cellular level, BNP reduced Ca(2+) transients and impaired Ca(2+) reuptake in the sarcoplasmic reticulum, in line with blunted SR Ca(2+) ATPase 2a and S100A1 expression. BNP increased Ca(2+) spark freque...
- by Jérémy Fauconnier and +2
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Duchenne muscular dystrophy (DMD) is characterized by myofiber death from apoptosis or necrosis, leading in many patients to fatal respiratory muscle weakness. Among other pathological features, DMD muscles show severely deranged... more
Duchenne muscular dystrophy (DMD) is characterized by myofiber death from apoptosis or necrosis, leading in many patients to fatal respiratory muscle weakness. Among other pathological features, DMD muscles show severely deranged metabolic gene regulation and mitochondrial dysfunction. Defective mitochondria not only cause energetic deficiency, but also play roles in promoting myofiber atrophy and injury via opening of the mitochondrial permeability transition pore. Autophagy is a bulk degradative mechanism that serves to augment energy production and eliminate defective mitochondria (mitophagy). We hypothesized that pharmacological activation of AMP-activated protein kinase (AMPK), a master metabolic sensor in cells and on-switch for the autophagymitophagy pathway, would be beneficial in the mdx mouse model of DMD. Treatment of mdx mice for 4 weeks with an established AMPK agonist, AICAR (5-aminoimidazole-4-carboxamide-1--D-ribofuranoside), potently triggered autophagy in the mdx diaphragm without inducing muscle fiber atrophy. In AICARtreated mdx mice, the exaggerated sensitivity of mdx diaphragm mitochondria to calcium-induced permeability transition pore opening was restored to normal levels. There were associated improvements in mdx diaphragm histopathology and in maximal force-generating capacity, which were not linked to increased mitochondrial biogenesis or up-regulated utrophin expression. These findings suggest that agonists of AMPK and other inducers of the autophagymitophagy pathway can help to promote the elimination of defective mitochondria and may thus serve as useful therapeutic agents in DMD. (Am J Pathol 2012,
- by Alain Lacampagne
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Calpains have been proposed to be involved in the cytoskeletal remodeling and wasting of skeletal muscle. However, limited data are available about the specific involvement of each calpain in the early stages of muscle atrophy. The aims... more
Calpains have been proposed to be involved in the cytoskeletal remodeling and wasting of skeletal muscle. However, limited data are available about the specific involvement of each calpain in the early stages of muscle atrophy. The aims of this study were to determine whether calpains 1 and 2 are autolyzed after a short period of muscle disuse, and, if so, where in the myofibers the autolyzed products are localized. In the rat soleus muscle, 5 days of immobilization increased autolyzed calpain 1 in the particulate and not the soluble fraction. Conversely, autolyzed calpain 2 was not found in the particulate fraction, whereas it was increased in the soluble fraction after immobilization. In the less atrophied plantaris muscle, no difference was noted between the control and immobilized groups whatever the fraction or calpain. Other proteolytic pathways were also investigated. The ubiquitin-proteasome pathway was activated in both skeletal muscles, and caspase 3 was activated only in the soleus muscle. Taken together, our data suggest that calpains 1 and 2 are involved in atrophy development in slow type muscle exclusively and that they have different regulation and protein targets. Moreover, the activation of proteolytic pathways appears to differ in slow and fast muscles, and the proteolytic mechanisms involved in fast-type muscle atrophy remain unclear.
Effects of chronic administration of clenbuterol on function and metabolism of adult rat cardiac muscle. Clenbuterol (Clen), a 2-agonist, is known to produce skeletal and myocardial hypertrophy. This compound has recently been used in... more
Effects of chronic administration of clenbuterol on function and metabolism of adult rat cardiac muscle. Clenbuterol (Clen), a 2-agonist, is known to produce skeletal and myocardial hypertrophy. This compound has recently been used in combination with left ventricular assist devices for the treatment of end-stage heart failure to reverse or prevent the adverse effects of unloading-induced myocardial atrophy. However, the mechanisms of action of Clen on myocardial cells have not been fully elucidated. In an attempt to clarify this issue, we examined the effects of chronic administration of Clen on Ca 2ϩ handling and substrate preference in cardiac muscle. Rats were treated with either 2 mg ⅐ kg Ϫ1 ⅐ day Ϫ1 Clen or saline (Sal) for 4 wk with the use of osmotic minipumps. Ventricular myocytes were enzymatically dissociated. Cells were field stimulated at 0.5, 1, and 2 Hz, and cytoplasmic Ca 2ϩ transients were monitored with the use of the fluorescent indicator indo-1 acetoxymethyl ester. Two-dimensional surface area and action potentials in current clamp were also measured. We found that in the Clen group there was significant hypertrophy at the organ and cellular levels compared with Sal. In Clen myocytes, the amplitude of the indo-1 ratio transients was significantly increased. Sarcoplasmic reticulum Ca 2ϩ content, estimated by rapid application of 20 mM caffeine, was significantly increased in the Clen group. The action potential was prolonged in the Clen group compared with Sal. Carbohydrate contribution to the tricarboxylic cycle (Krebs cycle) flux was increased several times in the Clen group. This increase was associated with decreased expression of peroxisome proliferator-activated receptor-␣. This study shows that chronic administration of Clen induces cellular hypertrophy and increases oxidative carbohydrate utilization together with an increase in sarcoplasmic reticulum Ca 2ϩ content, which results in increased amplitude of the Ca 2ϩ transients. These effects could be important when Clen is used in conjunction with left ventricular assist devices treatment.
Rationale: Diaphragmatic function is a major determinant of the ability to successfully wean patients from mechanical ventilation (MV). Paradoxically, MV itself results in a rapid loss of diaphragmatic strength in animals. However, very... more
Rationale: Diaphragmatic function is a major determinant of the ability to successfully wean patients from mechanical ventilation (MV). Paradoxically, MV itself results in a rapid loss of diaphragmatic strength in animals. However, very little is known about the time course or mechanistic basis for such a phenomenon in humans. Objectives: To determine in a prospective fashion the time course for development of diaphragmatic weakness during MV; and the relationship between MV duration and diaphragmatic injury or atrophy, and the status of candidate cellular pathways implicated in these phenomena. Methods: Airway occlusion pressure (TwPtr) generated by the diaphragm during phrenic nerve stimulation was measured in short-term (0.5 h; n 5 6) and long-term (.5 d; n 5 6) MV groups. Diaphragmatic biopsies obtained during thoracic surgery (MV for 2-3 h; n 5 10) and from brain-dead organ donors (MV for 24-249 h; n 5 15) were analyzed for ultrastructural injury, atrophy, and expression of proteolysis-related proteins (ubiquitin, nuclear factor-kB, and calpains). Measurements and Main Results: TwPtr decreased progressively during MV, with a mean reduction of 32 6 6% after 6 days. Longer periods of MV were associated with significantly greater ultrastructural fiber injury (26.2 6 4.8 vs. 4.7 6 0.6% area), decreased cross-sectional area of muscle fibers (1,904 6 220 vs. 3,100 6 329 mm 2 ), an increase of ubiquitinated proteins (119%), higher expression of p65 nuclear factor-kB (177%), and greater levels of the calcium-activated proteases calpain-1, -2, and -3 (1104%, 1432%, and 1266%, respectively) in the diaphragm. Conclusions: Diaphragmatic weakness, injury, and atrophy occur rapidly in critically ill patients during MV, and are significantly correlated with the duration of ventilator support.
In the heart, cAMP is a key regulator of excitation-contraction coupling and its biological effects are mainly associated with the activity of protein kinase A (PKA). The aim of this study was to investigate the contribution of the... more
In the heart, cAMP is a key regulator of excitation-contraction coupling and its biological effects are mainly associated with the activity of protein kinase A (PKA). The aim of this study was to investigate the contribution of the cAMP-binding protein Epac (Exchange protein directly activated by cAMP) in the regulation of the contractile properties of rat ventricular cardiac myocytes. We report that both PKA and Epac increased cardiac sarcomere contraction but through opposite mechanisms. Differently from PKA, selective Epac activation by the cAMP analog 8-(4-chlorophenylthio)-2-O-methyl-cAMP (8-pCPT) reduced Ca 2؉ transient amplitude and increased cell shortening in intact cardiomyocytes and myofilament Ca 2؉ sensitivity in permeabilized cardiomyocytes. Moreover, ventricular myocytes, which were infected in vivo with a constitutively active form of Epac, showed enhanced myofilament
- by Olivier Cazorla and +1
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Objective -To assess and compare cognitive levels and proÀ les of À ve cognitive functions according to hypertensive and heart failure status.
- by Olivier Cazorla and +1
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Ca sparks and the rate of SR Ca leak increased progressively with the duration of tachypacing, while diastolic [Ca]SR decreased with the duration of tachypacing. Na/Ca exchange activity was significantly augmented at 1 mo, and did not... more
Ca sparks and the rate of SR Ca leak increased progressively with the duration of tachypacing, while diastolic [Ca]SR decreased with the duration of tachypacing. Na/Ca exchange activity was significantly augmented at 1 mo, and did not change thereafter. The SERCA-mediated Ca uptake and the density of peak Ca current were not changed up to >8 mo of tachypacing. Progressive decreases in the amplitude of depolarization-induced Ca transients and singlecell contractions were observed only starting at the 4th month of tachypacing. These results suggest that diminished SR Ca release follows rather than precedes deterioration of in vivo cardiac function, thus is not likely to be a cause of HF.
The effects of 100 ,tM ryanodine on the L-type calcium channel were studied using the pacth-clamp technique in isolated guinea pig ventricular myocytes. The inactivation kinetics of the calcium current were slowed down in the presence of... more
The effects of 100 ,tM ryanodine on the L-type calcium channel were studied using the pacth-clamp technique in isolated guinea pig ventricular myocytes. The inactivation kinetics of the calcium current were slowed down in the presence of ryanodine in agreement with the blockade of the release of calcium from the sarcoplasmic reticulum by the drug. The I-V and steady-state inactivation curves of the calcium current were shifted to negative values by ryanodine. A similar shift was observed in the activation and inactivation curves of the intramembrane charge movement associated with the calcium channel. Due to this shift, ryanodine slightly reduced the maximal amount of displaced charge although it did not modify the transition from the inactivated to the activated state (i.e., charge movement repriming). This result is in notable contrast with that obtained in skeletal muscle, where it has been found that ryanodine interferes with charge movement repriming. These results provide additional evidence of the postulated differences between the architecture of the excitation-contraction coupling system in cardiac and skeletal muscle.
1 This study examined the effects of SR33805, a fantofarone derivative with reported strong Ca 2+antagonistic properties, on the contractile properties of intact and skinned rat ventricular myocytes. 2 On intact cells loaded with the Ca... more
1 This study examined the effects of SR33805, a fantofarone derivative with reported strong Ca 2+antagonistic properties, on the contractile properties of intact and skinned rat ventricular myocytes. 2 On intact cells loaded with the Ca 2+ -fluorescent indicator Indo-1, the application of low concentrations of SR33805 enhanced the amplitude of unloaded cell shortening and decreased the duration of cell shortening. Amplitude of the Ca 2+ transient was also decreased. 3 These effects were accompanied with a shortening of the action potential and a dose-dependent blockade of L-type calcium current (IC 50 ¼ 2.4 Â 10 À8 M). 4 On skinned cardiac cells, the application of a low SR33805 concentration (10 À8 M) induced a significant increase in maximal Ca 2+ -activated force at the two-tested sarcomere lengths (SLs), 1.9 and 2.3 mm. 5 The application of a larger dose of SR33805 (10 À6 -10 À5 M) induced a significant leftward shift of the tension -pCa relation that accounts for Ca 2+ -sensitization of the myofilaments, particularly at 2.3 mm SL. 6 In conclusion, despite its strong Ca 2+ -antagonistic properties SR33805 increases cardiac cell contractile activity as a consequence of its Ca 2+ -sensitizing effects. These effects are attributable to both an increase in the maximal Ca 2+ -activated force and a length-dependent Ca 2+ -sensitization.
1 This study examined the effects of SR33805, a fantofarone derivative with reported strong Ca 2+antagonistic properties, on the contractile properties of intact and skinned rat ventricular myocytes. 2 On intact cells loaded with the Ca... more
1 This study examined the effects of SR33805, a fantofarone derivative with reported strong Ca 2+antagonistic properties, on the contractile properties of intact and skinned rat ventricular myocytes. 2 On intact cells loaded with the Ca 2+ -fluorescent indicator Indo-1, the application of low concentrations of SR33805 enhanced the amplitude of unloaded cell shortening and decreased the duration of cell shortening. Amplitude of the Ca 2+ transient was also decreased. 3 These effects were accompanied with a shortening of the action potential and a dose-dependent blockade of L-type calcium current (IC 50 ¼ 2.4 Â 10 À8 M). 4 On skinned cardiac cells, the application of a low SR33805 concentration (10 À8 M) induced a significant increase in maximal Ca 2+ -activated force at the two-tested sarcomere lengths (SLs), 1.9 and 2.3 mm. 5 The application of a larger dose of SR33805 (10 À6 -10 À5 M) induced a significant leftward shift of the tension -pCa relation that accounts for Ca 2+ -sensitization of the myofilaments, particularly at 2.3 mm SL. 6 In conclusion, despite its strong Ca 2+ -antagonistic properties SR33805 increases cardiac cell contractile activity as a consequence of its Ca 2+ -sensitizing effects. These effects are attributable to both an increase in the maximal Ca 2+ -activated force and a length-dependent Ca 2+ -sensitization.