Intracellular calcium signals measured with indo-1 in isolated skeletal muscle fibres from control and mdx mice.
1. Intracellular free calcium concentration ([Ca2+]i) was measured with the fluorescent indicator indo-1 in single skeletal fibres enzymatically isolated from the flexor digitorum brevis and interosseus muscles of control and dystrophic mdx C57BL/10 mice. Measurements were taken from a portion of fibre that was voltage clamped to allow detection of depolarization-induced changes in [Ca2+]i. 2. The mean (+/- s.e.m.) initial resting [Ca2+]i from all control and mdx fibres tested was 56 +/- 5 nM (n = 72) and 48 +/- 7 nM (n = 57), respectively, indicating no significant overall difference between the two groups. However, when comparing a batch of control and mdx fibres obtained from mice older than approximately 35 weeks, resting [Ca2+]i was significantly lower in mdx (16 +/- 4 nM, n = 11) than in control fibres (71 +/- 10 nM, n = 14). 3. Changes in [Ca2+]i elicited by short (5-35 ms) depolarizing pulses from -80 to 0 mV showed similar properties in control and mdx fibres. After a 5 ms duration pulse the mean time constant of [Ca2+]i decay was, however, significantly elevated in mdx as compared to control fibres, by a factor of 1.5-2. For longer pulses, no significant difference could be detected. 4. In response to 50 ms duration depolarizing pulses of various amplitudes the threshold for detection of an [Ca2+]i change and the peak [Ca2+]i reached for a given potential were similar in control and mdx fibres. 5. Overall results show that mdx skeletal muscle fibres are quite capable of handling [Ca2+]i at rest and in response to membrane depolarizations.
Collet
C
C
Laboratoire de Physiologie des Elements Excitables, CNRS UMR 5578, Universite Claude Bernard Lyon 1, 43 boulevard du 11 Novembre 1918, 69622 Villeurbanne Cedex, France.
Allard
B
B
Tourneur
Y
Y
Jacquemond
V
V
D000367:Age Factors; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005456:Fluorescent Dyes; D005470:Fluorometry; D007211:Indoles; D008297:Male; D051379:Mice; D018101:Mice, Inbred mdx; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D018408:Patch-Clamp Techniques
D005456:Fluorescent Dyes; D007211:Indoles; C048960:indo-1; D002118:Calcium