Figure 5.

A typical example of the measurement of tension in an SF. (A) A bright-field image was used to track the electromagnetic needle and the particles. (B) A fluorescent image of the myosin II (arrows) label in the same field of view shown in panel A. Magnetic particles were also found in this fluorescent image perhaps because the particles were autofluorescent. Arrowheads in panels A and B show a magnetic particle that was confirmed to be bound with the SF. Bar = 10 μm. (C–I) Enlarged views of the area around the magnetic particle indicated by the arrowheads in panels A and B when external forces were applied. (C) Merged image of images at F = 0 (green) and 1000 pN (red). Bar = 1 μm. The applied forces were (D) F = 0, (E) F = 210, (F) F = 310, (G) F = 450, (H) F = 770, and (I) F = 1000 pN. (J) The relationship between external force, F, and displacement of the SFs. The displacement increased with an increase in F. (K) Calculated tensions (T_R′, T_L′) from Eqs. 3–6, and data for displacement and F. Fitted linear and dotted lines to plots were obtained by least-squares regression (T_L′ = 2.7 F + 1.2, R² = 0.86; T_R′ = 2.5F + 1.2, R² = 0.85). (In color online.)