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MATCHING OF SARCOPLASMIC RETICULUM AND CONTRACTILE PROPERTIES IN RAT FAST‐ AND SLOW‐TWITCH MUSCLE FIBRES
Author(s) -
Trinh Huong H,
Lamb Graham D
Publication year - 2006
Publication title -
clinical and experimental pharmacology and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 103
eISSN - 1440-1681
pISSN - 0305-1870
DOI - 10.1111/j.1440-1681.2006.04412.x
Subject(s) - fast twitch muscle , chemistry , endoplasmic reticulum , biophysics , myosin , soleus muscle , anatomy , troponin , sarcolemma , skeletal muscle , medicine , biochemistry , biology , myocardial infarction
SUMMARY1 The twitch characteristics (fast‐twitch or slow‐twitch) of skeletal muscle fibres are determined not only by the contractile apparatus properties of the fibre, but also by the time‐course of Ca 2+ release and re‐uptake by the sarcoplasmic reticulum (SR). The present study examined, in individual fibres from non‐transforming muscle of the rat, whether particular SR properties are matched to the contractile apparatus properties of the fibre, in particular in the case of fibres with fast‐twitch contractile apparatus located in a slow‐twitch muscle, namely the soleus. 2 Force was recorded in single, mechanically skinned fibres from extensor digitorum longus (EDL), gastrocnemius, peroneus longus and soleus muscles. Using repeated cycles in which the SR was emptied of all releasable Ca 2+ and then reloaded, it was possible to determine the relative amount of Ca 2+ present in the SR endogenously, the maximum SR capacity and the rate of Ca 2+ loading. The sensitivity of the contractile apparatus to Ca 2+ and Sr 2+ was used to classify the fibres as fast‐twitch (FT), slow‐twitch (ST) or mixed (< 3% of the fibres examined) and thereby identify the likely troponin C and myosin heavy chain types present. 3 There was no significant difference in SR properties between the groups of FT fibres obtained from the four different muscles, including soleus. Despite some overlap in the SR properties of individual fibres between the FT and ST groups, the properties of the FT fibres in all four muscles studied were significantly different from those of the ST and mixed fibres. 4 In general, in FT fibres the SR had a larger capacity and the endogenous Ca 2+ content was a relatively lower percentage of maximum compared with ST fibres. Importantly, in terms of their SR properties, FT fibres from soleus muscle more closely resembled FT fibres from other muscles than they did ST fibres from soleus muscle.