Figure 5.

Effects of compounds on skeletal and cardiac myofibrillar ATPase activity at high and low calcium concentrations. A, Ca²⁺-dependent ATPase activation of rabbit fast skeletal myofibrils (black filled squares, n = 8 independent preparations) and bovine cardiac myofibrils (red open squares, n = 10 independent preparations), without compounds. ATPase activities are normalized to the respective maximum ATP turnover rate at saturating Ca²⁺ concentration. B, concentration-dependent effects of mavacamten, a known cardiac-specific myosin inhibitor. C, effect of 50 μm compounds on ATPase activities at pCa 4, and D, at pCa 8, expressed as percent change in ATPase activity. Error bars indicate standard deviation (n ≥ 8). Significant difference (*) in drug effects on skeletal versus cardiac myofibril was established with Student's t test, p < 0.05.