Monitoring the structural behavior of troponin and myoplasmic free Ca2+ concentration during twitch of frog skeletal muscle.
The interaction of troponin molecules on the thin filament with Ca(2+) plays a key role in regulating muscle contraction. To characterize the structural changes of troponin caused by Ca(2+) and crossbridge formation, we recorded the small-angle x-ray intensity and the myoplasmic free Ca(2+) concentration using fluo-3 AM in the same frog skeletal muscle during twitch elicited by a single electrical pulse at 16 degrees C. In an overstretched muscle, the intensity of the meridional reflection from troponin at 1/38.5 nm(-1) began to change at 4 ms after the stimulus, reached a peak at 10 ms, and returned to the resting level with a halftime of 25 ms. The concentration of troponin-bound Ca(2+) began to increase at 1-2 ms after the stimulus, reached a peak at 5 ms, and returned to the resting level with a halftime of 40 ms, indicating that troponin begins to change conformation only after a sizable amount of Ca(2+) has bound to it, and returns to the resting structure even when there is still some bound Ca(2+). In a muscle with a filament overlap, crossbridge formation appears to slow down Ca(2+) release from troponin and have a large effect on its conformation.
Matsuo
Tatsuhito
T
Research and Utilization Division, Japan Synchrotron Radiation Research Institute, Hyogo, Japan.
Iwamoto
Hiroyuki
H
Yagi
Naoto
N
D008841:Actin Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D000814:Aniline Compounds / Q000378:metabolism; D000818:Animals; D001001:Anura; D001696:Biomechanical Phenomena; D002118:Calcium / Q000378:metabolism*; D003931:Diacetyl / Q000031:analogs & derivatives / Q000494:pharmacology; D007700:Kinetics; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D009210:Myofibrils / Q000187:drug effects / Q000378:metabolism*; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence; D017356:Synchrotrons; D013997:Time Factors; D014336:Troponin / Q000737:chemistry* / Q000378:metabolism; D014961:X-Ray Diffraction; D014966:Xanthenes / Q000378:metabolism
D000814:Aniline Compounds; D014336:Troponin; D014966:Xanthenes; C004717:diacetylmonoxime; C059715:Fluo-3; D003931:Diacetyl; D002118:Calcium