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This Article Full Text Full Text (PDF) All Versions of this Article: 92/2/437    most recent expphysiol.2006.036442v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Chen, W. Articles by Thompson, M. W. Search for Related Content PubMed PubMed Citation Articles by Chen, W. Articles by Thompson, M. W.

¹ School of Exercise and Sport Science, Faculty of Health Sciences, The University of Sydney, Sydney, NSW 1825, Australia ² Muscle Development Unit, Children's Medical Research Institute, Locked Bag 23, Wentworthville, NSW 2145, Australia

This study examined the effects of a bout of low-intensity, prolonged downhill exercise on sarcoplasmic reticulum (SR) Ca²⁺-ATPase activity, Ca²⁺ uptake and release in rat red vastus muscle. Ionophore stimulation was determined to assess vesicle integrity by measuring the ratio of Ca²⁺-ATPase activities in the presence and absence of A23187. [GenBank] Observations of the muscle ultrastructure were made to evaluate muscle damage at the level of the myofibrils and SR. Adult male Sprague–Dawley rats (weight, 395 ± 5.9 g) were either assigned as non-exercise controls or subjected to 90 min of downhill treadmill exercise (–16 deg; 15 m min^–1), and then killed immediately, 4, 24, 48, 72 or 144 h after exercise (n = 7). Calcium uptake was significantly lower (P < 0.05) compared with control values (19.25 ± 1.38 nmol min^–1 (mg protein)^–1), by 29 and 36% immediately and 4 h postexercise, respectively, and remained depressed (P < 0.05) 24 h postexercise. Calcium release was also significantly lower (P < 0.05) compared with control values (31.06 ± 2.36 nmol min^–1 (mg protein)^–1), by 37 and 39% immediately and 4 h postexercise, respectively, and remained depressed (P < 0.05) 24 h postexercise. Ca²⁺-ATPase activity measured with ionophore was 31% lower (P < 0.05) 4 h postexercise, and remained lower (P < 0.05) 24 h postexercise. The ratio of Ca²⁺-ATPase activities in the presence and absence of A23187 [GenBank] was not significantly changed after exercise, indicating that membrane integrity was not altered by the exercise. Focal dilatations of the SR were observed immediately and 4 h following exercise, implying that SR may be susceptible to damage in the localized regions of overstretched sarcomeres. The results demonstrate that a bout of low-intensity, prolonged downhill exercise results in a long-lasting depression of SR function that is not fully restored after 2 days of recovery, which may underlie some functional impairments induced by eccentric exercise.

(Received 8 November 2006; accepted after revision 26 November 2006; first published online 30 November 2006)
Corresponding author M. W. Thompson: School of Exercise & Sport Science, The University of Sydney, Sydney, NSW 1825, Australia. Email: m.thompson{at}fhs.usyd.edu.au

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