Premium
Mitochondrial and myoplasmic [Ca 2+ ] in single fibres from mouse limb muscles during repeated tetanic contractions
Author(s) -
Bruton Joseph,
Tavi Pasi,
Aydin Jan,
Westerblad Håkan,
Lännergren Jan
Publication year - 2003
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2003.00179.x
Subject(s) - stimulation , tetanic stimulation , mitochondrion , chemistry , soleus muscle , fast twitch muscle , anatomy , muscle fatigue , biophysics , calcium , medicine , endocrinology , biochemistry , skeletal muscle , biology , neuroscience , electromyography , receptor , organic chemistry , neurotransmission
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.