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Factors determining the subunit composition of tropomyosin in mammalian skeletal muscle.

ABSTRACT: Adult rat fast-twitch skeletal muscle such as extensor digitorum longus contains alpha- and beta-tropomyosin subunits, as is the case in the corresponding muscles of rabbit. Adult rat soleus muscle contains beta-, gamma- and delta-tropomyosins, but no significant amounts of alpha-tropomyosin. Evidence for the presence of phosphorylated forms of at least three of the four tropomyosin subunit isoforms was obtained, particularly in developing muscle. Immediately after birth alpha- and beta-tropomyosins were the major components of skeletal muscle, in both fast-twitch and slow-twitch muscles. Differentiation into slow-twitch skeletal muscles was accompanied by a fall in the amount of alpha-tropomyosin subunit and its replacement with gamma- and delta-subunits. After denervation and during regeneration after injury, the tropomyosin composition of slow-twitch skeletal muscle changed to that associated with fast-twitch muscle. Thyroidectomy slowed down the changes in tropomyosin composition resulting from the denervation of soleus muscle. The results suggest that the 'ground state' of tropomyosin-gene expression in the skeletal muscle gives rise to alpha- and beta-tropomyosin subunits. Innervation by a 'slow-twitch' nerve is essential for the expression of the genes controlling gamma- and delta-subunits. There appears to be reciprocal relationship between expression of the gene controlling the synthesis of alpha-tropomyosin and those controlling the synthesis of gamma- and delta-tropomyosin subunits.

SUBMITTER: Heeley DH

PROVIDER: S-EPMC1144733 | biostudies-other | 1985 Mar

REPOSITORIES: biostudies-other

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Project description:Parameters of patients' body composition have been suggested as prognostic markers in several clinical conditions including cancer and liver transplantation, but only limited data on its value in critical illness exist to date. In this study, we aimed at evaluating a potential prognostic value of the skeletal muscle mass and skeletal muscle myosteatosis of critically ill patients at admission to the ICU.DesignExploratory observational cohort study.SettingAn urban, academic medical institution.PatientsOne-hundred fifty-five patients treated for critical illness on a medical ICU.InterventionsNone.Measurements and main resultsWe used routine CT scans to assess the patients' individual body composition. The skeletal muscle index as a surrogate for sarcopenia was defined as the total skeletal muscle area at the level of the third lumbar vertebra on axial CT scan, normalized for the patient's height. Myosteatosis was evaluated by assessing the mean skeletal muscle attenuation measured in Hounsfield unit at the same sectional plane. The skeletal muscle index and mean skeletal muscle attenuation at admission to the ICU were significantly higher in patients with long-term survival (180-day or 1-year mortality), while both parameters were comparable between short-term survivors and nonsurvivors (ICU mortality or 30-d mortality). Patients with a skeletal muscle index or mean skeletal muscle attenuation below our established ideal cutoff values (74.95 mm2/cm and 29 Hounsfield unit) showed a significantly reduced overall survival. These findings were confirmed in univariate and multivariate Cox regression analyses. Furthermore, myosteatosis significantly correlated with the time of mechanical ventilation, the duration of hospital stay, and the presence of sepsis.ConclusionsOur data suggest that sarcopenia and myosteatosis represent important prognostic factors in critically ill patients that can be easily obtained from routine CT scans. Both parameters at admission to the ICU yield important information on the patients' long-term outcome and might be used for early clinical decision-making in these patients.

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Factors determining the subunit composition of tropomyosin in mammalian skeletal muscle.

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