Fast calcium removal during single twitches in amphibian skeletal muscle fibres

Citation
C. Caputo et al., Fast calcium removal during single twitches in amphibian skeletal muscle fibres, J MUSCLE R, 20(5), 1999, pp. 555-567
Citations number
39
Categorie Soggetti
Cell & Developmental Biology
Journal title
JOURNAL OF MUSCLE RESEARCH AND CELL MOTILITY
ISSN journal
01424319 → ACNP
Volume
20
Issue
5
Year of publication
1999
Pages
555 - 567
Database
ISI
SICI code
0142-4319(199908)20:5<555:FCRDST>2.0.ZU;2-2
Abstract
Fluorescence signals from the calcium sensitive dyes Fluo-3 or Rhod-2 were obtained simultaneously with isometric tension in single fibres isolated fr om the anterior tibialis muscle of Leptodactylus insularis (20-22 degrees C ). Fluo-3 fluorescence signals were transformed into [Ca2+](i) transients a s previously described. Most of the decay phase of single twitch transient is well fitted by a single exponential (tau of about 10 ms), followed by a slower declining component lasting tens of milliseconds. During short perio ds, 10 to 20 s, of low frequency stimulation, between 0.2 and 5 Hz, the bas al [Ca2+](i) increased slowly from 0.1 to about 0.4 mu M, with only minor c hanges in the exponentially decaying phase. In fibres poisoned with thapsig argin or cyclopiazonic acid (1-2 mu M) the tau of decay of fluorescence or Ca2+ transients of single twitches was very similar to that observed in non -poisoned fibres. Nevertheless, in poisoned fibres challenged with repetiti ve stimulation, the tau of Ca2+ transients decay increased from about 10 ms to > 40 ms, while the basal [Ca2+](i) increased from 0.1 to 2 mu M. Short rest periods (about 5 min) could reverse these effects, indicating that the y were not a direct consequence of SR Ca2+-ATPase inhibition. The correlati on coefficient between tau of decay and basal [Ca2+](i) was > 0.8 (P < 0.00 01). Qualitatively similar results were obtained measuring Rhod-2 fluoresce nce signals. A lumped, two-compartment model could account for these result s. Loading the fibres with EGTA-AM, diminished the effects of prolonged sti mulation observed in poisoned fibres. Moreover, we show that the Na+ - Ca2 exchange mechanism does not participate appreciably in fast Ca2+ removal.