FIGURE 5.

Class I and II HDAC inhibitors increase Ca²⁺ sensitivity of myofilaments. A, force-pCa curves generated from skinned fibers that were treated with vehicle (Me₂SO or IgG at 50 μg/ml, n = 5), the HDAC inhibitor trichostatin A (200 nm, n = 6), or anti-HDAC4 antibody (50 μg/ml, n = 6). Note, there is a significant increase (Student's t test, p < 0.05) in Ca²⁺ sensitivity as denoted by a leftward shift in the force-pCa curve generated from TSA and HDAC4 antibody-treated fibers, compared with vehicle-treated fibers. Values are mean ± S.E. B, Ca²⁺ sensitivity of skinned fibers treated with other HDAC inhibitors, MS-275 (5 μm) and Scriptaid (10 μm), and acetyl-CoA (AcCoA, 1 mm). There is a significant increase in Ca²⁺ sensitivity in all skinned fibers treated with HDAC inhibitors and acetyl-CoA (one-way analysis of variance, p < 0.05). Values are mean ± S.E. (n = 4-7). C, maximal activated force generated from different treatments. D and E, after measuring mechanical activity, skinned fibers were analyzed by Western blot analysis. Papillary (Pap.) muscle samples not subjected to skinning were utilized as controls. Note the presence of HDAC4 and PCAF in both papillary muscle and skinned fiber samples. However, other nuclear proteins such as SIRT1 and H2A were not detected in skinned fibers. ^*, signifies statistically significant compared with control (vehicle).