Muscle strength declines with age in part due to a decline of Ca2+ release from sarcoplasmic reticulum calcium stores. Skeletal muscle dihydropyridine receptors (Cav1.1) initiate muscle contraction by activating ryanodine receptors in the sarcoplasmic reticulum. Cav1.1 channel activity is enhanced by a retrograde stimulatory signal delivered by the ryanodine receptor. JP45 is a membrane protein interacting with Cav1.1 and the sarcoplasmic reticulum Ca2+ storage protein calsequestrin (CASQ1). Here we show that JP45 and CASQ1 strengthen skeletal muscle contraction by modulating Cav1.1 channel activity. Using muscle fibres from JP45 and CASQ1 double knockout mice, we demonstrate that Ca2+ transients evoked by tetanic stimulation are the result of massive Ca2+ influx due to enhanced Cav1.1 channel activity, which restores muscle strength in JP45/CASQ1 double knockout mice. We envision that JP45 and CASQ1 may be candidate targets for the development of new therapeutic strategies against decay of skeletal muscle strength caused by a decrease in sarcoplasmic reticulum Ca2+ content.
Malignant hyperthermia is a potentially fatal hypermetabolic disorder triggered by halogenated anesthetics and the myorelaxant succinylcholine in genetically predisposed individuals.Approximately 50% of Malignant Hyperthermia susceptible individuals carry dominant, gain of function mutations in RYR1 (which encodes ryanodine receptor type 1), though they have normal muscle function and no overt clinical symptoms. RyR1 is predominantly expressed in skeletal muscle but also to a lower extent in some immune and smooth muscle cells, suggesting that RYR1 mutations may have a wider range of effects than previously suspected. Consistently, reports describing mild bleeding abnormalities in patients with malignant hyperthermia carrying gain of function RYR1 mutations have appeared. In the present report we sought to determine the 3 frequency and molecular basis for this symptom. We found that some patients with specific RYR1 mutations had abnormally high bleeding scores, whereas their healthy relatives did not. Knock-in mice with the Malignant Hyperthermia Susceptibility RYR1 mutation Y522S (MHS RYR1 Y522S ) had bleeding times that were 3 times longer than their wild-type littermates. Primary vascular smooth muscle cells from RYR1 Y522S knock-in mice exhibited a higher frequency of subplasmalemmal Ca 2+ sparks leading to a more negative resting membrane potential. The bleeding defect of RYR1 Y522S mice and of one patient was reversed by treatment with the RYR1 antagonist dantrolene, and Ca 2+ sparks in primary vascular smooth muscle cells from the MHS RYR1 Y522S mice were blocked by ryanodine or dantrolene. Thus, RYR1 mutations may lead to prolonged bleeding by altering vascular smooth muscle cell function. The reversibility of the bleeding phenotype emphasizes the potential therapeutic value of dantrolene in the treatment of such bleeding disorders.4
The protein mammalian target of rapamycin (mTOR) is a serine/threonine kinase regulating a number of biochemical pathways controlling cell growth. mTOR exists in two complexes termed mTORC1 and mTORC2. Regulatory associated protein of mTOR (raptor) is associated with mTORC1 and is essential for its function. Ablation of raptor in skeletal muscle results in several phenotypic changes including decreased life expectancy, increased glycogen deposits and alterations of the twitch kinetics of slow fibres. In the present paper, we show that in muscle-specific raptor knockout (RamKO), the bulk of glycogen phosphorylase (GP) is mainly associated in its cAMP-non-stimulated form with sarcoplasmic reticulum (SR) membranes. In addition, 3[H]–ryanodine and 3[H]–PN200-110 equilibrium binding show a ryanodine to dihydropyridine receptors (DHPRs) ratio of 0.79 and 1.35 for wild-type (WT) and raptor KO skeletal muscle membranes respectively. Peak amplitude and time to peak of the global calcium transients evoked by supramaximal field stimulation were not different between WT and raptor KO. However, the increase in the voltage sensor-uncoupled RyRs leads to an increase of both frequency and mass of elementary calcium release events (ECRE) induced by hyper-osmotic shock in flexor digitorum brevis (FDB) fibres from raptor KO. The present study shows that the protein composition and function of the molecular machinery involved in skeletal muscle excitation–contraction (E–C) coupling is affected by mTORC1 signalling.
Background-Despite the use of heparin, aspirin, and other antiplatelet agents, acute coronary syndrome patients without ST-segment elevation remain at risk of cardiovascular thrombotic events. Given the role of inflammation in the pathogenesis of arterial thrombosis, we tested the hypothesis that the combination of meloxicam, a preferential COX-2 inhibitor, and heparin and aspirin would be superior to heparin and aspirin alone.
Methods and Results-In an open-label, randomized, prospective, single-blind pilot study, patients with acute coronary syndromes without ST-segment elevation were randomized to aspirin and heparin treatment (nϭ60) or aspirin, heparin, and meloxicam (nϭ60)
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