Étude du remodelage morphologique et électrophysiologique des cardiomyocytes ventriculaires chez le rat hypertendu TGR (mREN )27 et le rat obèse DIO

Le remodelage cardiaque regroupe les modifications survenant lorsque le cœur est soumis à diverses contraintes. Elles se traduisent notamment au niveau cellulaire par des changements électrophysiologiques. Grâce à la technique du " patch-clamp ", nous les avons étudiées au niveau des cardiomyocytes ventriculaires du rat hypertendu TGR (mREN2)27 et dans un modèle d'obésité, le rat DIOs (Diet Induced Obesity sensitive). Chez le rat TGR de 10 semaines, nos résultats montrent que le facteur surcharge de pression ne peut être seul à l'origine des modifications électrophysiologiques (allongement du potentiel d'action et réduction du courant Ito). De plus, l'étude à 14 mois met en évidence les interactions entre le remodelage lié au vieillissement et celui lié à l'hypertension artérielle. Enfin, chez les rats DIOs nos résultats suggèrent que la résistance à la leptine pourrait conduire l'échangeur Na-Ca à un fonctionnement arythmogèneLYON1-BU.Sciences (692662101) / SudocSudocFranceF

Accounting for cardiac t-tubule increase with age and myocyte volume to improve measurements of its membrane area and ionic current densities

International audienceIn-silico models of cardiac myocytes allow simulating experiments in numbers on series of myocytes as well as on large populations of myocytes assembled in 3D structures. The simulated myocyte populations should have realistic values and statistical dispersions of biophysical parameters such as myocyte dimensions and volume and areas of the peripheral membrane and transverse-axial tubular system (TATS). Dependencies among these variables also have to be taken into account. In this work, we propose a quantitative representation of the changes in the fraction of membrane area in the TATS that integrates published dependencies with body weight (age) and size of rat ventricular cardiac myocytes while respecting the above constraints. Imposing a constant total membrane area-to-volume ratio appears to account for the increase of this fraction with myocyte size (i.e.: volume) within a given age group. The agreement of our results with published data was discussed and reasons for discrepancies were analysed. On the basis of our framework, strategies are proposed for minimizing the influence of non-random dispersion related to myocyte volume on measurements of the area of TATS and surface membrane compartments and of ionic current densities. The next step will be to quantitatively compare these strategies by evaluating the impact of myocyte morphological parameters and their dependencies, sample size, biases and errors, on the output of experiments

Caveolin-3 is a direct molecular partner of the Cav1.1 subunit of the skeletal muscle L-type calcium channel.

International audienceCaveolin-3 is the striated muscle specific isoform of the scaffolding protein family of caveolins and has been shown to interact with a variety of proteins, including ion channels. Mutations in the human CAV3 gene have been associated with several muscle disorders called caveolinopathies and among these, the P104L mutation (Cav-3(P104L)) leads to limb girdle muscular dystrophy of type 1C characterized by the loss of sarcolemmal caveolin. There is still no clear-cut explanation as to specifically how caveolin-3 mutations lead to skeletal muscle wasting. Previous results argued in favor of a role for caveolin-3 in dihydropyridine receptor (DHPR) functional regulation and/or T-tubular membrane localization. It appeared worth closely examining such a functional link and investigating if it could result from the direct physical interaction of the two proteins. Transient expression of Cav-3(P104L) or caveolin-3 specific siRNAs in C2C12 myotubes both led to a significant decrease of the L-type Ca(2+) channel maximal conductance. Immunolabeling analysis of adult skeletal muscle fibers revealed the colocalization of a pool of caveolin-3 with the DHPR within the T-tubular membrane. Caveolin-3 was also shown to be present in DHPR-containing triadic membrane preparations from which both proteins co-immunoprecipitated. Using GST-fusion proteins, the I-II loop of Ca(v)1.1 was identified as the domain interacting with caveolin-3, with an apparent affinity of 60nM. The present study thus revealed a direct molecular interaction between caveolin-3 and the DHPR which is likely to underlie their functional link and whose loss might therefore be involved in pathophysiological mechanisms associated to muscle caveolinopathies

New mode of action for a knottin bioinsecticide: Pea Albumin 1 subunit b (PA1b) is the first peptidic inhibitor of V-ATPase.

International audiencePA1b (for Pea Albumin 1 subunit b) is a plant bioinsecticide lethal for several pests which are important in agriculture or human health. PA1b belongs to the inhibitory cystine knot (ICK) family or knottin family. Originating from a plant (the garden pea) commonly eaten by humans without any known toxic or allergic effects, PA1b is a candidate for transgenic applications and is one of the most promising biopesticide for pest control. Using whole-cell patch clamp techniques on Sf9 PA1b-sensible Lepidopteran insect cells, we discover that PA1b reversibly blocks ramp membrane currents in a dose dependent manner (EC50 = 0.52 uM). PA1b has the same effect as bafilomycin, a specific inhibitor of the vacuolar proton pump (V-H+-ATPase), and the PA1b-sensitive current depends on the internal proton concentration. Biochemical assays on purified V-ATPase from the Lepidopteran model Manduca sexta showed that PA1b inhibits the V1V0-H+ ATPase holoenzyme activity (IC50 ca. 70 nM), by interacting with the membrane bound V0 part of the V-ATPase. V-ATPase is a complex protein which is increasingly studied because of its numerous physiological roles. In the midgut of insects, V-ATPase activity is essential for energizing nutrient absorption and the results reported in this paper explain the entomotoxic properties of PA1b. Targeting V-ATPase is a promising means of combating insect pests, and PA1b represents the first peptidic V-ATPase inhibitor. The search for V-ATPase inhibitors is currently booming, since it has been demonstrated that V-ATPase plays a role in so many physiological processes