The Effect of Exercise-training on Sarcoplasmic Reticulum Function in Fast and Slow Skeletal Muscle
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The effect of endurance exercise on the capacity of crube homogenates (CH) to sequester Ca2+ was determined in the slow type I soleus, the fast type IIA deep region of the vastus lateralis (DVL), and the fast type IIB superficial region of the vastus lateralis (SVL). The Ca2+ uptake capacity was affected by exercise in a fiber type specific manner. The fast-twitch SVL showed a 35% decrease in the maximal rate of Ca2+ uptake (Vmax) and a significantly lower Km while the slow soleus and fast DVL were unaltered. The time course of Ca2+ uptake, and the peak amount of Ca2+ sequestered was not altered by exercise in any of the muscles studied. The homogenates from the exercise-trained soleus muscles exhibited an increased ability to retain Ca2+ and in this capacity became more like fast muscle.