Contents
|
|
Programme
Contents
|
Recently we showed that mdx (animal model of Duchenne muscular dystrophy) muscle fibres are more susceptible to stretch-induced muscle damage and there is an associated rise in resting [Ca2+]i (Yeung et al., 2005). We propose that elevated [Ca2+]i causes reactive oxygen species (ROS) production, leading to muscle damage. Thus treatment with ROS scavenger may exert a protective effect against stretch-induced muscle damage. To test this hypothesis, single fibres isolated from the flexor digitorum brevis of the mdx mice were subjected to 10 stretched contractions (eccentric contractions), stretched by 30 % of optimal length (Lo) during each tetanus. Measurements of intracellular calcium with fluo-4 were obtained using confocal microscopy. Calibration of fluo-4 intensities were performed using the procedure described by Kao et al. (1989).
The resting [Ca2+]i in the mdx fibres was 227 ± 44 nM (n = 5), significantly higher than that in the wild-type fibres (100 ± 6 nM, n=3, P < 0.05). Under control conditions in the mdx muscle, [Ca2+]i increased slowly following stretched contractions to 690 ± 64 nM (n= 9) after 20 min. The ROS scavenger 4,5-dihydroxy-1,3-benzenedisulfonic acid (Tiron, 5 mM) was applied during and for 30 min following the stretched contractions in 6 mdx fibres. Not only did Tiron prevent the rise in [Ca2+]i (145 ± 21 nM, P<0.0001) at 20 min, it also improved the force following stretched contractions from 35 ± 4% to 59 ± 7 % (P<0.05).
These results indicate that production of ROS play a role in stretch-induced muscle damage in mdx fibres and, further, suggest that ROS may have a role in the activation of stretch-activated channels which produce the Ca2+ entry.
Kao, J.P., Harootunian, A.T. & Tsien, R.Y. (1989) Journal of Biological Chemistry, 264, 8179-84.
Yeung, E.W., Whitehead, N.P., Suchyna, T.M., Gottlieb, P.A., Sachs, F. & Allen, D.G. (2005) Journal of Physiology 562, 367-80.