Fluorescence changes from single striated muscle fibres injected with labelled troponin C (TnCDANZ).
A fluorescently labelled derivative of the calcium binding subunit of troponin, TnC, has been injected into isolated striated muscle fibres from the barnacle Balanus nubilus. The Ca2+ affinity of isolated TnC is close to that of intact troponin when located in the thin filament. Excitation of the TnCDANZ within the muscle cell (325nm) revealed a marked fluorescence at 510 nm and was similar to that observed in vitro, which was absent at 400 or 600 nm after subtraction of the fibre autofluorescence. High Ca2+ salines increased the fluorescence at 510 nm by roughly 2 times. Single voltage clamp pulses produced a rapid rise in fluorescence at 510 nm after allowing for any non-specific changes at 400 nm, and this signal preceded force development by approx. 55 ms at 22 degrees C. It reached a maximum at the same time as force and subsequently decayed more slowly. The fluorescence signal increased in magnitude with increase in stimulus intensity. These results suggest that Ca2+ attaches rapidly to the contractile filament, but is lost relatively slowly and imply a slow decay of the activation process.
D000818:Animals; D002118:Calcium / Q000378:metabolism; D003619:Dansyl Compounds; D005456:Fluorescent Dyes; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism; D009119:Muscle Contraction / Q000187:drug effects; D009132:Muscles / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D001468:Thoracica; D014336:Troponin / Q000031:analogs & derivatives
D003619:Dansyl Compounds; D005456:Fluorescent Dyes; D014336:Troponin; C043338:dansylaziridine-troponin C; D008274:Magnesium; D002118:Calcium