Increasing myosin light chain 3f (MLC3f) protects against a decline in contractile velocity

Disuse induces adaptations in skeletal muscle, which lead to muscle deterioration. Hindlimb-unloading (HU) is a well-established model to investigate cellular mechanisms responsible for disuse-induced skeletal muscle dysfunction. In myosin heavy chain (MHC) type IIB fibers HU induces a reduction in contraction speed (Vo) and a reduction in the relative myosin light chain 3f (MLC3f) protein content compared with myosin light chain 1f (MLC1f) protein. This study tested the hypothesis that increasing the relative MLC3f protein content via rAd-MLC3f vector delivery would attenuate the HU-induced decline in Vo in single MHC type IIB fibers. Fischer-344 rats were randomly assigned to one of three groups: control, HU for 7 days, and HU for 7 days plus rAd-MLC3f. The semimembranosus muscles were injected with rAd-MLC3f (3.75 x 1011-5 x 1011 ifu/ml) at four days after the initiation of HU. In single MHC type IIB fibers the relative MLC3f content decreased by 25% (12.00±0.60% to 9.06±0.66%) and Vo was reduced by 29% (3.22±0.14fl/s vs. 2.27±0.08fl/s) with HU compared to the control group. The rAd-MLC3f injection resulted in an increase in the relative MLC3f content (12.26±1.19%) and a concomitant increase in Vo (2.90±0.15fl/s) of MHC type IIB fibers. A positive relationship was observed between the percent of MLC3f content and Vo. Maximal isometric force and specific tension were reduced with HU by 49% (741.45±44.24μN to 379.09±23.77μN) and 33% (97.58±4.25kN/m2 to 65.05±2.71kN/m2), respectively compared to the control group. The rAd-MLC3f injection did not change the HU-induced decline in force or specific tension. Collectively, these results indicate that rAd-MLC3f injection rescues hindlimb unloading-induced decline in Vo in MHC type IIB single muscle fibers.Published versio

Reduced current density and surface expression of a CLCN1 mutation causing dominant or recessive myotonia in Costa Rica

Mutations in CLCN1 coding for the muscle ClC-1 Cl- channel lead to dominant (Thomsen's disease) of recessive (Becker's disease) myotonia. Here we characterized several CLCN1 mutations identified in Costa Rica myotonia patients: Q412P (Morales 2008. RevBiolTrop 56:1), R105C, Q154R, and F167L (R105C and F167L have been described earlier in German families (Meyer-Kleine 1995. AmJHumGenet57:1325, Zhang 2000. Neurology54:937). In different families, the Q412P mutation was found to be inherited both in recessive and dominant fashion. We studied the Cl- currents generated by these mutants in Xenopus oocytes using electrophysiological techniques, and for the Q412P mutant also surface membrane expression. Assaying for fast and common gating properties and single channel conductance, we found that none of the mutations exhibited significant alterations of gating parameters or conductance. In fact, mutations R105C, Q154R, and F167L were indistinguishable from WT ClC-1 (in agreement with earlier studies for R105C and F167L (Desaphy 2013, ExpNeurol 248:530). However, mutation Q412P displayed a dramatically reduced current density and a reduced surface expression. However, mimicking the heterozygous status of patients by co-injecting WT and mutant RNA in a 1:1 ratio did not reveal a significant reduction of current density compared to the injection of the half amount of WT. Our results indicate that Q412P does not exert a dominant negative effect on WT and that the pathophysiology of the R105C, Q154R, and F167L mutations is not due to reduced open probability or single channel current, but that these mutations must affect mechanisms that are not well reproduced in a non-skeletal muscle expression systems. The lack of dominance of Q412P might be due to early protein degradation (before being able to interact with WT subunits) or to a silent phenotype in WT/Q412P heteromers.Telethon Italy (grant GGP 12008 to M.P.), the Jepa Limmatfoundation, the Compagnia San Paolo (M.P.); SAF2012-31486, 2012 SGR719 and ICREA Academia Prize (RE)Universidad de Costa Rica/[742-B4-318]/UCR/Costa RicaConsejo Nacional para Investigaciones Científicas y Tecnológicas/[]/CONICIT/Costa RicaMinisterio de Ciencia, Innovación, Tecnología y Telecomunicaciones/[]/MICITT/Costa RicaTelethon Italia/[GGP 12008]/ItaliaJepa-Limmat Foundation/[]//ItaliaCompagnia di San Paolo/[]//ItaliaCompagnia di San Paolo/[SAF2012-31486]//ItaliaCompagnia di San Paolo/[2012 SGR719]//ItaliaICREA Acadèmia Prize/[]/EspañaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias de la Salud::Instituto de Investigaciones en Salud (INISA)UCR::Vicerrectoría de Docencia::Salud::Facultad de Medicin

Indicators of physical stress during hindlimb suspension in Wistar rats / Indicadores de stress físico durante a suspensão dos membros inferiores em ratos Wistar

Hindlimb suspension (HS) has been used in animal research as a microgravity simulation model. However, physical stress to the animals during suspension has received little attention. The purpose of this work was to investigate physical stress, oxidative stress, and cross-sectional area (CSA) in rats submitted to hindlimb suspension. Twelve male Wistar rats were allocated into two groups: control (CON, n = 6); hindlimb suspension (HS, n = 6), for ten days. The following signs of physical stress were monitored: bristly hair, spleen hair, edema in the nose, edema or necrosis in the tail, edema in the hind legs, aggressiveness, redness in the dorsal region, body weight loss, and food intake. Samples of the soleus and tibialis anterior were prepared for CSA and carbonylated proteins analysis. The frequency of the signs of stress, except redness in the dorsal region, was significantly higher (P <.05) in the HS group. CSA of soleus (816.6µm2, 95%CI: 866.3-904.0 vs 1158.8mm2, 95%CI: 1171.9-1214.2) and tibialis anterior (1041.5µm2, 95%CI: 1119.1-1185.2 vs 1429.8µm2, 95%CI: 1479.2-1566.4) were lower in the HS group (P <.05). Carbonylated proteins in the soleus (2779.0 ± 1319.8 AU vs 1063.2 ± 289.2 AU) and tibialis anterior (1155.8 AU, 95%CI: 80.0-4064.5 vs 108.4 AU, 95%CI: 35.5-320.7) were higher in the HS group (P <.05). The suspension model evokes oxidative stress and reduced CSA. However, several signs of physical stress can occur. This indicates that hindlimb suspension models may introduce confounding factors that influence muscle atrophy and should be used cautiously.

Gas-phase basicity of methionine.

International audienceProton affinity and protonation entropy of methionine (Met) were determined by the extended kinetic method from ESI-Q-TOF tandem mass spectrometry experiments. The values, PA(Met) = 937.5 +/- 2.9 kJ mol(-1) and Delta(p)S degrees (Met) = - 22 +/- 5 J mol(-1) K(-1), lead to gas-phase basicity GB(Met) = 898.2 +/- 3.2 kJ.mol(-1). Quantum chemical calculations using density functional theory confirm that the proton affinity of Met is indeed in the 940 kJ mol(-1) range and that a significant entropy loss, of at least - 25 J mol(-1) K(-1), occurs upon protonation. This last point is evidenced here for the first time and suggests revision of the tabulated protonation thermochemistry of Met. A comparison with previous experimental data allows us to propose the following evaluated thermochemical values: PA(Met) = 943 +/- 4 kJ mol(-1) and Delta(p)S degrees (Met) = - 35 +/- 15 J mol(-1) K(-1) and GB(Met) = 900 +/- 2 kJ mol(-1)

Molecular determinants of state-dependent block of voltage-gated sodium channels by pilsicainide

Background and purpose: Pilsicainide, an anti-arrhythmic drug used in Japan, is described as a pure sodium channel blocker. We examined the mechanisms by which it is able to block open channels, because these properties may be especially useful to reduce hyperexcitability in pathologies characterized by abnormal sodium channel opening. Experimental approach: The effects of pilsicainide on various heterologously expressed human sodium channel subtypes and mutants were investigated using the patch clamp technique. Key results: Pilsicainide exhibited tonic and use-dependent effects comparable to those of mexiletine and flecainide on hNav1.4 channels. These use-dependent effects were abolished in the mutations F1586C and Y1593C within segment 6 of domain IV, suggesting that the interaction of pilsicainide with these residues is critical for its local anaesthetic action. Its affinity constants for closed channels (KR) and channels inactivated from the closed state (KI) were high, suggesting that its use-dependent block (UDB) requires the channel to be open for it to reach a high-affinity blocking site. Accordingly, basic pH, which slightly increased the proportion of neutral drug, dramatically decreased KR and KI values. Effects of pilsicainide were similar on skeletal muscle hNav1.4, brain hNav1.1 and heart hNav1.5 channels. The myotonic R1448C and G1306E hNav1.4 mutants were more and less sensitive to pilsicainide, respectively, due to mutation-induced gating modifications. Conclusions and implications: Although therapeutic concentrations of pilsicainide may have little effect on resting and closed-state inactivated channels, it induces a strong UDB due to channel opening, rendering the drug ideally suited for inhibition of high-frequency action potential firing