Shortening of a myofibril during contraction is prevented by light cross-linking with 1-ethyl-3-carbodiimide.
The signal is contributed by approximately 12 labeled actin molecules. In this method, the detection volume is made shallow by TIR illumination, and narrow by confocal aperture inserted in the conjugate image plane. Fluorescence anisotropy, indicating orientation of an actin protomer, is collected from a volume of a few attoliters (10−18 L) by confocal total internal reflection (CTIR) microscopy. This work introduces such a method, which analyzes fluctuations of anisotropy of a few actin molecules in muscle.
Studying cross-bridge dynamics during isometric steady-state contraction requires an equilibrium time-resolved method (not involving application of a transient). It is not self-evident, however, that the mechanical cycle occurs during steady-state isometric contraction where no work is produced. Cyclic interactions of myosin and actin are responsible for contraction of muscle.
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