Protein kinase C α and ε phosphorylation of troponin and myosin binding protein C reduce Ca2+ sensitivity in human myocardium

Previous studies indicated that the increase in protein kinase C (PKC)-mediated myofilament protein phosphorylation observed in failing myocardium might be detrimental for contractile function. This study was designed to reveal and compare the effects of PKCα- and PKCε-mediated phosphorylation on myofilament function in human myocardium. Isometric force was measured at different [Ca2+] in single permeabilized cardiomyocytes from failing human left ventricular tissue. Activated PKCα and PKCε equally reduced Ca2+ sensitivity in failing cardiomyocytes (ΔpCa50 = 0.08 ± 0.01). Both PKC isoforms increased phosphorylation of troponin I- (cTnI) and myosin binding protein C (cMyBP-C) in failing cardiomyocytes. Subsequent incubation of failing cardiomyocytes with the catalytic subunit of protein kinase A (PKA) resulted in a further reduction in Ca2+ sensitivity, indicating that the effects of both PKC isoforms were not caused by cross-phosphorylation of PKA sites. Both isozymes showed no effects on maximal force and only PKCα resulted in a modest significant reduction in passive force. Effects of PKCα were only minor in donor cardiomyocytes, presumably because of already saturated cTnI and cMyBP-C phosphorylation levels. Donor tissue could therefore be used as a tool to reveal the functional effects of troponin T (cTnT) phosphorylation by PKCα. Massive dephosphorylation of cTnT with alkaline phosphatase increased Ca2+ sensitivity. Subsequently, PKCα treatment of donor cardiomyocytes reduced Ca2+ sensitivity (ΔpCa50 = 0.08 ± 0.02) and solely increased phosphorylation of cTnT, but did not affect maximal and passive force. PKCα- and PKCε-mediated phosphorylation of cMyBP-C and cTnI as well as cTnT decrease myofilament Ca2+ sensitivity and may thereby reduce contractility and enhance relaxation of human myocardium

Cardiac myosin binding protein C phosphorylation in cardiac disease

Perturbations in sarcomeric function may in part underlie systolic and diastolic dysfunction of the failing heart. Sarcomeric dysfunction has been ascribed to changes in phosphorylation status of sarcomeric proteins caused by an altered balance between intracellular kinases and phosphatases during the development of cardiac disease. In the present review we discuss changes in phosphorylation of the thick filament protein myosin binding protein C (cMyBP-C) reported in failing myocardium, with emphasis on phosphorylation changes observed in familial hypertrophic cardiomyopathy caused by mutations in MYBPC3. Moreover, we will discuss assays which allow to distinguish between functional consequences of mutant sarcomeric proteins and (mal)adaptive changes in sarcomeric protein phosphorylation

La problématique de l’éclairage et de la modulation dans “Le Poème pulvérisé” de René Char

L'après-guerre est un temps de rupture pour René Char. L’engagement résistant terminé, la fin de la guerre lui apporte un sentiment de solitude qui donne à sa poésie un chemin différent. Avec "Le Poème pulvérisé" la poésie devient une lutte contre l'inéluctable avancée du temps. Contre cette linéarité du temps le poète retrouve des instants exceptionnels qui sortent l'homme de sa chute continuelle vers la mort. La langue se morcelle en mots qui sont là-devant et dans ce morcèlement qui module, le poète retrouve des moments éclairants qui offrent une modalité d'existence authentique. Ce mémoire se propose d'analyser comment la familiarité quotidienne qui tombe en miettes relève la présence fulgurante d'un état ekstatique. Transformation et échange entre différents éléments, la modulation ne suppose pas la conversion d'un élément en son contraire, mais l'actualisation d'un troisième élément authentique qui devient leur fondement. Nous analysons la modulation à tous les niveaux de la poésie : stylistique, narratif, symbolique et ontologique pour dégager les instances d'une langue fragmentée où l'instant ne se situe pas dans la succession chronologique du temps, il est l'exception, il est le temps de l'éclairage.Arts, Faculty ofFrench, Hispanic, and Italian Studies, Department ofGraduat