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Exposure of mammalian skeletal muscle to sub-physiological temperatures reduces its ability to function at physiological temperatures

J. Edwards, C. van der Poel and D.G. Stephenson, Department of Zoology, La Trobe University, VIC 3086, Australia.

Most studies using isolated mammalian skeletal muscle preparations are conducted at temperatures well below physiological temperatures (17-25°C) because the performance of isolated mammalian skeletal muscle preparations dramatically and irreversibly drops when preparations are re-exposed to normal body core temperatures around 37°C (Lännergren & Westerblad 1987; Ranatunga 1998; Coupland & Ranatunga 2003). This loss in force may be the result of re-heating the preparation during experimental procedures.

In order to test the hypothesis that re-heating isolated skeletal muscle fibre preparations to physiological temperature causes damage to the muscle, rat EDL fibre bundles were excised (30-50 fibres) either at 22°C or in a temperature-controlled room at 37°C from Long Evans (Hooded) rats killed by halothane overdose in accordance with the LTU Animal Ethics Committee. The muscles were then attached to a force transducer, stretched to optimum length and tetanically stimulated every 10 min until force could not be measured whilst immersed in a Krebs-Ringer solution (KRS) maintained at 37°C. KRS contained (mM); NaCl 122, KCl 2.8, CaCl2 1.3, MgSO4 1.2, KH2PO4 1.2, NaHCO3 25 and D-glucose 5, (constantly bubbled with carbogen: 95% oxygen, 5% carbon dioxide).

The results show that after 30 min of exposure to solution maintained at 37°C, tetanic force dropped dramatically to 3.4 ± 0.1% of initial tetanic force in muscle preparations that were dissected at 22°C and then re-heated, whereas after the same length of time, tetanic force dropped to only 68.0 ± 7.8% of initial tetanic force in muscle preparations dissected and kept throughout at 37°C. This marked decrease in tetanic force appears to be associated with an increase in free radical O2· production when preparations are re-heated. These results show that preventing isolated mammalian skeletal muscle from dropping below core body temperature during dissection helps maintain its function when working at 37°C.

Coupland, M.E. & Ranatunga, K.W. (2003) Journal of Physiology 548(Pt 2), 439-49.

Lännergren, J. & Westerblad, H. (1987) Journal of Physiology 390, 285-93.

Ranatunga, K.W. (1998) Experimental Physiology 83(3), 371-6.


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