Glycogen content and excitation-contraction coupling in mechanically skinned muscle fibres of the cane toad
Article first published online: 7 SEP 2004
The Journal of Physiology
Volume 519, Issue 1, pages 177–187, August 1999
How to Cite
Stephenson, D. G., Nguyen, L. T. and Stephenson, G. M. M. (1999), Glycogen content and excitation-contraction coupling in mechanically skinned muscle fibres of the cane toad. The Journal of Physiology, 519: 177–187. doi: 10.1111/j.1469-7793.1999.0177o.x
- Issue published online: 7 SEP 2004
- Article first published online: 7 SEP 2004
- (Received 4 February 1999; accepted after revision 5 May 1999)
- 1Mechanically skinned skeletal muscle fibres from the twitch region of the iliofibularis muscle of cane toads were used to investigate the relationship between fibre glycogen content and fibre capacity to respond to transverse tubular (T-) system depolarization.
- 2A large proportion of total fibre glycogen remained in mechanically skinned muscle fibres exposed to aqueous solutions. This glycogen pool (about 80 % of total fibre glycogen) was very stable when the preparation was incubated in a rigor solution (pH 7.0) but decreased gradually at a rate of 0.59 ± 0.20 % min−1 in a relaxing solution (200 nM [Ca2+]). The rate was considerably higher (2.66 ± 0.38 % min−1) when the preparations were exposed to 30 μM [Ca2+]. An even greater rate of glycogen loss was found after T-system depolarization-induced contractions. The Ca2+-dependent loss of fibre glycogen was caused by endogenous glycogenolytic processes.
- 3Silver stained SDS gels of components eluted into relaxing solution from single skinned fibres revealed a rapid (2 min) loss of parvalbumin and at least 10 other proteins varying in molecular mass between 10 and 80 kDa but there was essentially no loss of myosin heavy and light chains and actin. Subsequent elution for a further 30 min in either relaxing or maximally Ca2+-activating solution did not result in additional, appreciable detectable loss of fibre protein.
- 4Depletion of fibre glycogen was associated with loss of fibre ability to respond to T-system depolarization even though the bathing solutions contained high levels of ATP (8 mM) and creatine phosphate (10 mM).
- 5The capacity of mechanically skinned fibres to respond to T-system depolarization was highly positively correlated (P < 0.0001) with initial fibre glycogen concentration.
- 6In conclusion, the results show that (i) the capacity of skeletal muscle to respond to T-system depolarization is related directly or indirectly to the non-washable glycogen pool in fibres, (ii) this relationship holds for conditions where glycogen is not required as a source of energy and (iii) the mechanically skinned fibre preparation is well suited to study the regulation of endogenous glycogenolytic enzymes.