Contractile properties of single-skinned skeletal muscle fibres of the extensor digitorum longus muscle of the Australian short-nosed echidna
Anthony J. Bakker A D , Ann L. Parkinson B and Stewart I. Head CA Physiology, School of Biomedical and Chemical Sciences, University of Western Australia, Perth, WA 6009, Australia.
B Faculty of Science, University of the Sunshine Coast, Maroochydore DC, Qld 4558, Australia.
C School of Physiology and Pharmacology, University of New South Wales, Sydney, NSW 2052, Australia.
D Corresponding author. Email: abakker@cyllene.uwa.edu.au
Australian Journal of Zoology 53(4) 237-240 https://doi.org/10.1071/ZO05011
Submitted: 1 March 2005 Accepted: 22 June 2005 Published: 6 September 2005
Abstract
Eutherian mammal fast-twitch muscle fibres share similar contractile activation properties, suggesting that these properties are highly conserved in mammals. To investigate this hypothesis, we examined the contractile properties of skeletal muscle from the order Monotremata, a mammalian order that separated from eutherians 150 million years ago. The Ca2+- and Sr2+-activation properties of single mechanically skinned skeletal muscle fibres from the extensor digitorum longus (EDL) muscle of the short-nosed echidna were determined. Sigmoidal curves fitted to force response data plotted as a function of pCa (–log[Ca2+]), had a mean slope of 4.32 ± 0.28 and a mean pCa50 and pCa10 value of 6.18 ± 0.01 and 6.41 ± 0.02 respectively (n = 20). The mean pSr50, pSr10 and slope values of curves fitted to the force-response data after activation with Sr2+ were 4.80 ± 0.03, 5.29 ± 0.07 and 2.75 ± 0.18 respectively (n = 20). The mean pCa50–pSr50 value for the echidna EDL fibres was 1.37 ± 0.04. In five of the echidna fibres, exposure to submaximal Ca2+ concentrations produced myofibrillar force oscillations (mean frequency, 0.13 ± 0.01 Hz), a phenomenon found only in eutherian slow and intermediate muscle fibres. These results show that echidna EDL fibres generally have similar contractile properties to eutherian fast-twitch skeletal muscle fibres, such as those found in the EDL of the rat.
Acknowledgments
We thank Professor M. Rowe and Mr G. Coleman for providing us with the echidna skeletal muscle for these experiments.
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