Figure 4.

Simultaneous stretching and shortening of α-actinin periodicity in contracting stress fibers. (A) Well-spread Swiss 3T3 cell maintained in serum showing GFP-α-actinin distribution before stimulation. (B) Enlarged area from (A) illustrating sarcomeric unit of stress fibers and center-to-center spacing used to measure “sarcomere” length. (C-E) Measurements of sarcomere length over time showed no change in unstimulated cells (C), but revealed simultaneous stretching and shortening of sarcomeres in cells stimulated with 5 nM calyculin A (D) or LPA (E).