A new muscle contractile system composed of a thick filament lattice and a single actin filament.
To bridge the gap between the contractile system in muscle and in vitro motility assay, we have devised an A-band motility assay system. A glycerinated skeletal myofibril was treated with gelsolin to selectively remove the thin filaments and expose a single A-band. A single bead-tailed actin filament trapped by optical tweezers was made to interact with the inside or the outer surface of the A-band, and the displacement of the bead-tailed filament was measured in a physiological ionic condition by phase-contrast and fluorescence microscopy. We observed large back-and-forth displacement of the filament accompanied by a large change in developed force. Despite this large tension fluctuation, we found that the average force was proportional to the overlap inside and outside the A-band up to approximately 150 nm and 300 nm from the end of the A-band, respectively. Consistent with the difference in the density of myosin molecules, the average force per unit length of the overlap inside the A-band (the time-averaged force/myosin head was approximately 1 pN) was approximately twice as large as that outside. Thus, we conclude that the A-band motility assay system described here is suitable for studying force generation on a single actin filament, and its sliding movement within a regular three-dimensional thick filament lattice.
Suzuki
Madoka
M
Department of Physics, School of Science and Engineering, Waseda University, Tokyo, Japan.
Fujita
Hideaki
H
Ishiwata
Shin'ichi
S
D008841:Actin Cytoskeleton / Q000737:chemistry; D000199:Actins / Q000737:chemistry* / Q000502:physiology; D000818:Animals; D018260:Gelsolin / Q000737:chemistry; D005990:Glycerol / Q000737:chemistry; D007477:Ions; D008297:Male; D008856:Microscopy, Fluorescence; D008858:Microscopy, Phase-Contrast; D009119:Muscle Contraction; D009132:Muscles / Q000378:metabolism; D011817:Rabbits; D012518:Sarcomeres / Q000378:metabolism; D013997:Time Factors
D000199:Actins; D018260:Gelsolin; D007477:Ions; D005990:Glycerol