Mitochondrial and myoplasmic [Ca2+] in single fibres from mouse limb muscles during repeated tetanic contractions
Previous studies on single fast-twitch fibres from mouse toe muscles have shown marked fatigue-induced changes in the free myoplasmic [Ca 2+ ] ([Ca 2+ ] i ), while mitochondrial [Ca 2+ ] remained unchanged. We have now investigated whether muscle fibres from the legs of mice respond in a similar way...
Saved in:
Published in | The Journal of physiology Vol. 551; no. 1; pp. 179 - 190 |
---|---|
Main Authors | , , , , |
Format | Journal Article |
Language | English |
Published |
England
The Physiological Society
15.08.2003
Blackwell Science Inc |
Subjects | |
Online Access | Get full text |
Cover
Loading…
Summary: | Previous studies on single fast-twitch fibres from mouse toe muscles have shown marked fatigue-induced changes in the free
myoplasmic [Ca 2+ ] ([Ca 2+ ] i ), while mitochondrial [Ca 2+ ] remained unchanged. We have now investigated whether muscle fibres from the legs of mice respond in a similar way. Intact,
single fibres were dissected from the soleus and extensor digitorum longus (EDL) muscles of adult mice. To measure [Ca 2+ ] i , indo-1 was injected into the isolated fibres. Mitochondrial [Ca 2+ ] was measured using Rhod-2 and confocal laser microscopy. Fatigue was induced by up to 1000 tetanic contractions (70 Hz)
given at 2 s intervals. In soleus fibres, there was no significant decrease in tetanic [Ca 2+ ] i at the end of the fatiguing stimulation, whereas tetanic force was significantly reduced by about 30 %. In 10 out of 14 soleus
fibres loaded with Rhod-2 and subjected to fatigue, mitochondrial [Ca 2+ ] increased to a maximum after about 50 tetani; this increase was fully reversed within 20 min after the end of stimulation.
The force-frequency curve of the non-responding soleus fibres was shifted to higher frequencies compared to that of the responding
fibres. In addition, eight out of nine Rhod-2-loaded EDL fibres showed similar changes in mitochondrial [Ca 2+ ] during and after a period of fatiguing stimulation. The stimulation-induced increase in mitochondrial [Ca 2+ ] was reduced when mitochondria were depolarised by application of carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone, whereas
it was increased by application of an inhibitor of the mitochondrial Na + /Ca 2+ exchange (CGP-37157). In conclusion, isolated slow-twitch muscle fibres show only modest changes in tetanic force and [Ca 2+ ] i during repeated contractions. The increase in mitochondrial Ca 2+ does not appear to be essential for activation of mitochondrial ATP production, nor does it cause muscle damage. |
---|---|
Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0022-3751 1469-7793 |
DOI: | 10.1113/jphysiol.2003.043927 |