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Am J Physiol Cell Physiol (March 7, 2007). doi:10.1152/ajpcell.00052.2007
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Submitted on February 5, 2007
Accepted on March 5, 2007

Effects of elevated physiological temperatures on sarcoplasmic reticulum function in mechanically skinned muscle fibers of the rat

Chris van der Poel1 and D George Stephenson2*

1 Zoology, La Trobe University, Melbourne, Victoria, Australia
2 Zoology, LaTrobe University, Melbourne, Victoria, Australia

* To whom correspondence should be addressed. E-mail: george.stephenson{at}latrobe.edu.au.

Properties of the sarcoplasmic reticulum (SR) with respect to Ca2+-loading and release were measured in mechanically-skinned fiber preparations from isolated extensor digitorum longus (EDL) muscles of the rat that were either kept at room temperature (23°C) or exposed to temperatures in the upper physiological range for mammalian skeletal muscle (30min at 40°C or 43°C). The ability of the SR to accumulate Ca2+ was significantly reduced by a factor of 1.9-2.1 after the temperature treatments due to a marked increase in SR Ca2+-leak, which persisted for at least 3 hours after treatment. Results with blockers of Ca2+-release channels (Ruthenium Red) and SR Ca2+-pumps (2,5-di(tert-butyl)-1,4-hydroquinone (TBQ)), indicate that the increased Ca2+-leak was not through the SR Ca2+-release channel or the SR Ca2+-pump, although it is possible that the leak pathway was via oligomerised Ca2+-pump molecules. No significant change in the maximum SR Ca2+-ATPase activity was observed after the temperature treatment, although there was a tendency for a decrease in the SR Ca2+-ATPase. The observed changes in SR properties were fully prevented by the superoxide (O2-) scavenger Tiron (20mM) indicating that the production of O2- at elevated temperatures is responsible for the increase in SR Ca2+-leak. Results show that physiologically relevant elevated temperatures (i) induce lasting changes in SR properties with respect to Ca2+-handling which contribute to a marked increase in the SR Ca2+-leak and consequently to the reduction in the average coupling ratio between Ca2+-transport and SR Ca2+-ATPase and muscle performance, and (ii) that these changes are mediated by temperature-induced O2- production.




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