Figure 8.

Sarcomere length traces exhibited a prominent “bump” during lightly loaded shortening following sMyBP-C dephosphorylation by lambda phosphatase treatment (red). (A and B) Representative sarcomere length shortening into the C-zone traces following PKA (A, green) and lambda phosphatase (B, red). Trace averages are shown in purple following PKA (A) and lambda phosphatase (B). (C) Sarcomere length trace bumps were manipulated by slight alteration of load clamps. Increasing the load clamp by ∼5% intervals caused a greater time delay in the sarcomere bump, i.e., sarcomeres shortened more slowly ostensibly causing thin filaments to engage the C-zone at a later time point. (D) Sarcomere length traces exhibited a biphasic lengthening when exiting the apparent C-zone (black; n = 3). The rate of lengthening increased as sarcomeres lengthened beyond ∼3.05 µm. When the fiber preparation was stretched to a sarcomere length of ∼3.08 µm, the sarcomeres exhibited a more linear lengthening during supra-isometric load clamps (gray).