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J J Mercadier

Publications and source records attributed to J J Mercadier.

At least 55 records · Page 3Linked to original sources
PubMed1995

Nitric oxide regulates the calcium current in isolated human atrial myocytes.

Cardiac Ca2+ current (ICa) was shown to be regulated by cGMP in a number of different species. Recently, we found that the NO-donor SIN-1 (3-morpholino-sydnonimine) exerts a dual regulation of ICa in frog ventricular myocytes via an accumulation of cGMP. To examine whether NO also regulates Ca2+ channels in human heart, we investigated the effects of SIN-1 on ICa in isolated human atrial myocytes. An extracellular application of SIN-1 produced a profound stimulatory effect on basal ICa at concentrations > 1 pM. Indeed, 10 pM SIN-1 induced a approximately 35% increase in ICa. The stimulatory effect of SIN-1 was maximal at 1 nM (approximately 2-fold increase in ICa) and was comparable with the effect of a saturating concentration (1 microM) of isoprenaline, a beta-adrenergic agonist. Increasing the concentration of SIN-1 to 1-100 microM reduced the stimulatory effect in two thirds of the cells. The stimulatory effect of SIN-1 was not mimicked by SIN-1C, the cleavage product of SIN-1 produced after liberation of NO. This suggests that NO mediates the effects of SIN-1 on ICa. Because, in frog heart, the stimulatory effect of SIN-1 on ICa was found to be due to cGMP-induced inhibition of cGMP-inhibited phosphodiesterase (cGI-PDE), we compared the effects of SIN-1 and milrinone, a cGI-PDE selective inhibitor, on ICa in human. Milrinone (10 microM) induced a strong stimulation of ICa (approximately 150%), demonstrating that cGI-PDE controls the amplitude of basal ICa in this tissue. In the presence of milrinone, SIN-1 (0.1-1 nM) had no stimulatory effect on ICa, suggesting that the effects of SIN-1 and MIL were not additive. We conclude that NO may stimulate ICa in human atrial myocytes via inhibition of the cGI-PDE.

Adolescent↗
PubMed1995

Genetic linkage heterogeneity in myotubular myopathy.

Myotubular myopathy is a severe congenital disease inherited as an X-linked trait (MTM1; McKusick 31040). It has been mapped to the long arm of chromosome X, to the Xq27-28 region. Significant linkage has subsequently been established for the linkage group comprised of DXS304, DXS15, DXS52, and F8C in several studies. To date, published linkage studies have provided no evidence of genetic heterogeneity in severe neonatal myotubular myopathy (XLMTM). We have investigated a family with typical XLMTM in which no linkage to these markers was found. Our findings strongly suggest genetic heterogeneity in myotubular myopathy and indicate that great care should be taken when using Xq28 markers in linkage studies for prenatal diagnosis and genetic counseling.

Chromosome Mapping↗
PubMed1994

A new human slow skeletal troponin T (TnTs) mRNA isoform derived from alternative splicing of a single gene.

A human muscle cDNA library was screened for slow skeletal troponin T (TnTs). Sequence analysis revealed that one of the selected clones had a cDNA coding sequence different from the two previously described. RNase protection assays confirmed the expression of this new isoform in adult skeletal muscle. In addition, results of the RNase protection assays strongly suggested the expression of a fourth isoform. These isoforms for human slow TnT most likely result from combinatorial alternative splicing of a single gene.

Adult↗
PubMed1993

Molecular cloning and developmental expression of human cardiac troponin T.

We have isolated a full-size cDNA coding for cardiac troponin T (cTnT) from a human adult heart library, using a slow skeletal TnT probe. This cDNA detected a 1.2 kb mRNA in fetal and post-natal human heart, the amount of which increased during ontogenic development. Interestingly, a similar transcript was coexpressed in fetal skeletal muscle, together with the 0.9 kb slow skeletal muscle mRNA, and its expression was down-regulated during further development.

Adult↗
PubMed1993

Mechanical properties of rat cardiac skinned fibers are altered by chronic growth hormone hypersecretion.

Chronic growth hormone (GH) hypersecretion in rats leads to increased isometric force without affecting the unloaded shortening velocity of isolated cardiac papillary muscles, despite a marked isomyosin shift toward V3. To determine if alterations occurred at the level of the contractile proteins in rats bearing a GH-secreting tumor (GH rats), we examined the mechanical properties of skinned fibers to eliminate the early steps of the excitation-contraction coupling mechanism. We found that maximal active tension and stiffness at saturating calcium concentrations (pCa 4.5) were markedly higher in GH rats than in control rats (tension, 52.9 +/- 5.2 versus 38.1 +/- 4.6 mN.mm-2, p < 0.05; stiffness, 1,105 +/- 120 versus 685 +/- 88 mN.mm-2.microns-1, p < 0.01), whereas values at low calcium concentrations (pCa 9) were unchanged. In addition, the calcium sensitivity of the contractile proteins was slightly but significantly higher in GH rats than in control rats (delta pCa 0.04, p < 0.001). The crossbridge cycling rate, reflected by the response to quick length changes, was lower in GH rats than in control rats (62.0 +/- 2.6 versus 77.4 +/- 6.6 sec-1, p < 0.05), in good agreement with a decrease in the proportion of alpha-myosin heavy chains in the corresponding papillary muscles (45.5 +/- 2.0% versus 94.6 +/- 2.4%, p < 0.001). The changes in myosin heavy chain protein phenotype were paralleled by similar changes of the corresponding mRNAs, indicating that the latter occurred mainly at a pretranslational level. These results demonstrate that during chronic GH hypersecretion in rats, alterations at the myofibrillar level contribute to the increase in myocardial contractility observed in intact muscle.

Animals↗
PubMed1993

Chronic growth hormone (GH) hypersecretion induces reciprocal and reversible changes in mRNA levels from hypothalamic GH-releasing hormone and somatostatin neurons in the rat.

Effects of growth hormone (GH) hypersecretion on somatostatin-(SRIH) and GH-releasing hormone (GHRH) were studied by in situ hybridization and receptor autoradiography in rats bearing a GH-secreting tumor. 6 and 18 wk after tumor induction, animals displayed a sharp increase in body weight and GH plasma levels; pituitary GH content was reduced by 47 and 55%, while that of prolactin and thyrotropin was unchanged. At 18 wk, hypothalamic GHRH and SRIH levels had fallen by 84 and 52%, respectively. In parallel, the density of GHRH mRNA per arcuate neuron was reduced by 52 and 50% at 6 and 18 wk, while SRIH mRNA levels increased by 71 and 83% in the periventricular nucleus (with no alteration in the hilus of the dentate gyrus). The numbers of GHRH- and SRIH-synthetizing neurons in the hypothalamus were not altered in GH-hypersecreting rats. Resection of the tumor restored hypothalamic GHRH and SRIH mRNAs to control levels. GH hypersecretion did not modify 125I-SRIH binding sites on GHRH neurons. Thus, chronic GH hypersecretion affects the expression of the genes encoding for GHRH and SRIH. The effect is long lasting, not desensitizable and reversible.

Animals↗
PubMed1993

[Plasticity of myocardial phenotype during cardiac hypertrophy and failure].

Cardiac hypertrophy and failure frequently cause complications in some cardiovascular diseases. Both conditions are associated with important modifications of the heart's contractile and endocrine functions, induced by various changes in gene expression, which in turn are attributable to chronic hemodynamic overload. Differential expression of the myosin heavy chain family leads to a disproportionate accumulation of the alpha form relative to the beta, which in turn causes slower but more efficient myocardial contraction. This transition occurs in the rodent ventricle and human atrium. In the sarcomeric actin family, both the alpha-cardiac and alpha-skeletal isoforms are expressed in the mammalian ventricle in utero. After birth, the latter transiently accumulates in the rodent ventricle at the acute phase of an experimental overload. In humans, alpha-skeletal actin accounts for over half of total actin; this ratio remains the same during heart failure. In experimental models of hemodynamic overload, and during heart failure in humans, expression of Ca(2+)-ATPase in the sarcoplasmic reticulum is reduced. This decrease may partly account for the changes in cardiac relaxation observed in these circumstances. The atrial natriuretic factor gene in the ventricular myocardium is also activated, permitting the ventricle to participate in the regulation of its loading conditions. Several mechanical and neurohumoral factors have been proposed as triggers for this gene reprogramming. Research is currently focussed on signal transduction mechanisms, and in particular identification of the transcription factors involved.

Animals↗
PubMed1992

Contractile proteins and sarcoplasmic reticulum calcium-ATPase gene expression in the hypertrophied and failing heart.

The physiology of myocardial contractility has been studied for over a century, but only recently has molecular biology provided new insights into the mechanisms responsible for the alterations of contraction and relaxation observed during cardiac hypertrophy and heart failure. Pressure and volume overload produce in the myocyte both qualitative changes characterized by protein isoform switches and quantitative changes characterized by modulation of single genes through a mechanogenic transduction the pathways of which are largely unknown. The qualitative changes involve differential expression of multigene families of contractile proteins, especially myosin heavy chain (MHC) and actin. All situations of pressure overload, or of combined pressure and volume overload activate the beta-MHC gene and deactivate the alpha-MHC one, which leads to a slower, more efficient contraction. In rat, pressure overload transitorily activates the alpha-skeletal actin gene, and both the timing and the distribution of the newly formed beta-MHC and alpha-skeletal actin mRNAs differ. We recently found that the isoactin pattern is the same in patients with end-stage heart failure as that of control human hearts. Moreover, both in rat and human, expression of isomyosins and isoactins are not coordinated, neither during ontogeny nor senescence. All this suggests the existence of several regulatory mechanisms activated during normal cardiac growth or by a mechanical trigger, and preliminary results indicate that it is possible to perform nuclear run-on assays in order to analyze the transcriptional step of these isogenes.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed1992

Switches in cardiac muscle gene expression as a result of pressure and volume overload.

In the mammalian heart, the expression of genes encoding proteins responsible for contraction, relaxation, and endocrine function changes in hypertrophy resulting from hemodynamic overload. Different mechanisms are involved in this mechanogenic transduction, including 1) differential expression of myosin and actin multigene families, which may account for the decreased velocity of contractile element shortening in hypertrophied heart, 2) nonactivation of the sarcoplasmic reticulum Ca(2+)-ATPase gene, which may explain the increased duration of isometric relaxation, and finally 3) activation in the ventricle of the atrial natriuretic factor gene that is responsible in part for the high plasma levels of this peptide. It is increasingly apparent that these changes are independently regulated, but little is known about the mechanisms underlying this regulation. Preliminary results indicate that it is now possible to analyze the early time course or transcription for each gene after the imposition of hemodynamic overload. This should significantly enhance our understanding of the regulatory mechanisms involved in the phenoconversions of the hemodynamically overloaded heart.

Actins↗
PubMed1992

Effects of chronic growth hormone excess on cardiac contractility and myosin phenotype in the rat.

The effects of chronic growth hormone (GH) hypersecretion on intrinsic contractile properties of the myocardium were studied in rats bearing a GH-secreting tumour. Body weight and heart weight increased, but no true cardiac hypertrophy was observed. The maximum active force of left ventricular papillary muscle was increased, and the maximum shortening velocity of the unloaded muscle was unaltered. This was despite a marked shift of the myosin isoforms towards the low ATPase activity V3 form, which was associated with a similar shift of myosin mRNAs. Total ATPase activity, measured on frozen sections, was unaltered suggesting, together with the results of the mechanical study, an increase in the number of active enzymatic sites. Studies performed on skinned fibres confirmed the increased myocardial contractility, thus suggesting that myocardial adaptation to chronic GH excess occurred, at least in part, at the level of the myofibrillar contractile apparatus.

Animals↗
PubMed1991

Skeletal actin mRNA increases in the human heart during ontogenic development and is the major isoform of control and failing adult hearts.

Expression of the two sarcomeric actins, alpha-skeletal and alpha-cardiac, is regulated in the rodent heart in response to developmental, hormonal, and hemodynamic stimuli. Little is known in man, except that both isogenes were found to be coexpressed in three adult ventricles. In this report, we investigated the isoactin mRNA composition in ventricles from 21 control patients (4 fetal, 5 juvenile, 12 adult) and from 15 patients undergoing cardiac transplantation (5 idiopathic dilated cardiomyopathies, 5 ischemic myopathies with myocardial infarcts, 5 diverse etiologies) by two different and complementary techniques: RNA dot blot analysis with specific cDNA probes, and primer extensions with an oligonucleotide common to alpha-cardiac and alpha-skeletal actins. In the case of dot blot analysis, quantification of each isoform was performed by using as standards RNA transcripts obtained from cloned human alpha-actin sequences, and the total amount of sarcomeric actin mRNA was evaluated as a function of total poly(A+)RNA. We found that both isogenes are always coexpressed, and that the isoactin pattern changes during development. In utero and in neonatal hearts, alpha-skeletal actin mRNA represents less than or equal to 20% of sarcomeric actins, it increases to 48 +/- 6% during the first decade after birth and becomes the predominant isoform of adult hearts (60.4 +/- 8.5%). The 15 adult failing hearts exhibited the same isoactin pattern as the control ones (62.84 +/- 11.06%), and there was no difference in expression between patients with dilated cardiomyopathy or ischemic heart disease. These observations demonstrate that cardiac development in man, in contrast to rodent heart, is characterized by an up-regulation of the skeletal actin gene, the expression of which does not change in hypertrophied and failing hearts, and suggest that the actin and myosin heavy chain families are independently regulated in human heart.

Actins↗
PubMed1990

Synthesis and secretion of atrial natriuretic factor during chronic hypoxia: a study in the conscious instrumented rat.

1. To investigate the mechanisms leading to enhanced synthesis and release of atrial natriuretic factor during chronic hypoxia, we measured immunoreactive plasma atrial natriuretic factor, blood gases, packed cell volume, pulmonary artery pressure and systemic artery pressure in male Sprague-Dawley rats exposed to 1, 2 or 3 weeks of normobaric hypoxia. Rats were implanted with pulmonary and carotid artery catheters and studied conscious, 23 h after return to hypoxia. 2. The concentration of atrial natriuretic factor messenger RNA was measured in the right and left ventricular free walls of rats exposed to 3 weeks of hypoxia and in normoxic control rats. 3. There was a trend for plasma atrial natriuretic factor to increase with the duration of exposure to hypoxia but only the 3-week hypoxic rats had a significantly higher level (1080 +/- 193 pg/ml) than the normoxic control rats (318 +/- 46 pg/ml, P less than 0.05, mean +/- SEM). When all the data from normoxic and hypoxic rats were considered together, plasma atrial natriuretic factor was positively correlated with packed cell volume (r = 0.66, P less than 0.001), pulmonary artery pressure (r = 0.68, P less than 0.002), and the index of right ventricular hypertrophy (r = 0.54, P less than 0.01), but after analysis of partial correlation, packed cell volume was the only independent contributing factor to the variance in the level of plasma atrial natriuretic factor (r2 = 0.24).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Urinary cyclic guanosine monophosphate as an indicator of experimental congestive heart failure in rats.

STUDY OBJECTIVE--The aim was to investigate the relationship between urinary cyclic guanosine monophosphate (GMP) excretion and activation of the heart endocrine function in two rat models of cardiac failure. DESIGN--Left ventricular infarction and aging in spontaneously hypertensive rats (SHR) are two models that could lead to congestive heart failure. In the first the degree of failure depends on the length of the infarcted area. In the second the degree of failure depends on time. Urinary cyclic GMP, plasma atrial natriuretic factor (ANF), and degree of congestive heart failure were evaluated in both models. EXPERIMENTAL ANIMALS--31 male Wistar rats were used for myocardial infarction and sham operated controls. Spontaneously hypertensive (SHR) rats (2, 6, 12 and 24 months old, n = 10 per group) were used for the age overload studies. MEASUREMENTS AND MAIN RESULTS--In myocardial infarction, the amount of left ventricular ANF mRNA, plasma ANF concentration, and urinary cyclic GMP excretion were correlated and were proportional to the degree of cardiac failure, as assessed by the increase in right ventricular mass and the decrease in blood pressure. In male SHR (aged 6-24 months), plasma ANF and urinary cyclic GMP were correlated, increased with age, and were proportional to the heart to body weight ratio. These correlations between plasma ANF, daily urinary cyclic GMP excretion, and left ventricular hypertrophy persisted in two year old SHR. The presence of pleural extravasation in these old animals was also characterised by significant increases in both plasma ANF and urinary cyclic GMP. The plasma ANF and the daily urinary cyclic GMP excretion were negative prognostic indicators of life expectancy in two year old SHR. CONCLUSIONS--Urinary cyclic GMP excretion, correlated with the plasma ANF level, is a non-invasive indicator of congestive heart failure in two models of overloaded left ventricle in rats.

Aging↗
PubMed1990

Function of the sarcoplasmic reticulum and expression of its Ca2(+)-ATPase gene in pressure overload-induced cardiac hypertrophy in the rat.

The reduction in Ca2+ concentration during diastole and relaxation occurs differently in normal hearts and in hypertrophied hearts secondary to pressure overload. We have studied some possible molecular mechanisms underlying these differences by examining the function of the sarcoplasmic reticulum and the expression of the gene encoding its Ca2(+)-ATPase in rat hearts with mild and severe compensatory hypertrophy induced by abdominal aortic constriction. Twelve sham-operated rats and 31 operated rats were studied 1 month after surgery. Eighteen animals exhibited mild hypertrophy (left ventricular wt/body wt less than 2.6) and 13 animals severe hypertrophy (left ventricular wt/body wt greater than 2.6). During hypertrophy we observed a decline in the function of the sarcoplasmic reticulum as assessed by the oxalate-stimulated Ca2+ uptake of homogenates of the left ventricle. Values decreased from 12.1 +/- 1.2 nmol Ca2+/mg protein/min in sham-operated rats to 9.1 +/- 1.5 and 6.7 +/- 1.1 in rats with mild and severe hypertrophy, respectively (p less than 0.001 and p less than 0.001, respectively, vs. shams). This decrease was accompanied by a parallel reduction in the number of functionally active CA2(+)-ATPase molecules, as determined by the level of Ca2(+)-dependent phosphorylated intermediate: 58.8 +/- 7.4 and 48.1 +/- 13.5 pmol P/mg protein in mild and severe hypertrophy, respectively, compared with 69.7 +/- 8.2 in shams (p less than 0.05 and p less than 0.01, respectively, vs. shams). Using S1 nuclease mapping, we observed that the Ca2(+)-ATPase messenger RNA (mRNA) from sham-operated and hypertrophied hearts was identical. Finally, the relative level of expression of the Ca2(+)-ATPase gene was studied by dot blot analysis at both the mRNA and protein levels using complementary DNA clones and a monoclonal antibody specific to the sarcoplasmic reticulum Ca2(+)-ATPase. In mild hypertrophy, the concentrations of Ca2(+)-ATPase mRNA and protein in the left ventricle were unchanged when compared with shams (mRNA, 93.8 +/- 10.6% vs. sham, NS; protein, 105.5 +/- 14% vs. sham, NS). in severe hypertrophy, the concentration of Ca2(+)-ATPase mRNA decreased to 68.7 +/- 12.9% and that of protein to 80.1 +/- 15.5% (p less than 0.001 and p less than 0.05, respectively), whereas the total amount of mRNA and enzyme per left ventricle was either unchanged or slightly increased. The slow velocity of relaxation of severely hypertrophied heart can be at least partially explained by the absence of an increase in the expression of the Ca2(+)-ATPase gene and by the relative diminution in the density of the Ca2+ pumps.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Altered sarcoplasmic reticulum Ca2(+)-ATPase gene expression in the human ventricle during end-stage heart failure.

A decrease in the myocardial level of the mRNA encoding the Ca2(+)-ATPase of the sarcoplasmic reticulum (SR) has been recently reported during experimental cardiac hypertrophy and failure. To determine if such a deficit occurs in human end-stage heart failure, we compared the SR Ca2(+)-ATPase mRNA levels in left (LV) and right ventricular (RV) specimens from 13 patients undergoing cardiac transplantation (6 idiopathic dilated cardiomyopathies; 4 coronary artery diseases with myocardial infarctions; 3 diverse etiologies) with control heart samples using a rat cardiac SR Ca2(+)-ATPase cDNA probe. We observed a marked decrease in the mRNA for the Ca2(+)-ATPase relative to both the 18S ribosomal RNA and the myosin heavy chain mRNA in LV specimens of patients with heart failure compared to controls (-48%, P less than 0.01 and -47%, P less than 0.05, respectively). The LV ratio of Ca2(+)-ATPase mRNA to 18S RNA positively correlated with cardiac index (P less than 0.02). The RV ratio correlated negatively with systolic, diastolic and mean pulmonary arterial pressures (P less than 0.02, P less than 0.02, and P less than 0.01, respectively). We suggest that a decrease of the SR Ca2(+)-ATPase mRNA in the myocardium plays an important role in alterations of Ca2+ movements and myocardial relaxation reported during human end-stage heart failure.

Adult↗
PubMed1990

Effects of chronic growth hormone hypersecretion on intrinsic contractility, energetics, isomyosin pattern, and myosin adenosine triphosphatase activity of rat left ventricle.

We studied papillary muscle mechanics and energetics, myosin phenotype, and ATPase activities in left ventricles from rats bearing a growth hormone (GH)--secreting tumor. 18 wk after tumor induction, animals exhibited a dramatic increase in body weight (+101% vs. controls) but no change in the ventricular weight/body weight ratio. The maximum isometric force of papillary muscles normalized per cross-sectional area rose markedly (+42%, P less than 0.05 vs. controls), whereas the maximum unloaded shortening velocity did not change. This was observed despite a marked isomyosin shift towards V3 (32 +/- 5% vs. 8 +/- 2% in controls, P less than 0.001). Increased curvature of the force-velocity relationship (+64%, P less than 0.05 vs. controls) indicated that the muscles contracted more economically, suggesting the involvement of V3 myosin. Total calcium- and actin-activated myosin ATPase activities assayed on quickly frozen left ventricular sections were similar in tumor-bearing rats and in controls. After alkaline preincubation, these activities only decreased in tumor-bearing rats, demonstrating that V3 enzymatic sites were involved in total ATPase activity. These data demonstrate that chronic GH hypersecretion in the rat leads to a unique pattern of myocardial adaptation which allows the muscle to improve its contractile performance and economy simultaneously, thanks to myosin phenoconversion and an increase in the number of active enzymatic sites.

Actomyosin↗