Gliding velocities of actin filaments and native ventricular and M. soleus thin filaments on native tissue purified ventricular and M. soleus β-/slow myosin on a nitrocellulose-coated assay chamber surface. (A) Movement of F-actin (0.101 ± 0.007 µm/s SE, n = 7 assay chambers) and of M. soleus native thin filaments (0.082 ± 0.004 µm/s SE, n = 21) on M. soleus myosin. (B) Movement of F-actin on ventricular β-myosin molecules (0.200 ± 0.010 µm/s SE, n = 6) was significantly slower than that of thin filaments prepared from ventricular myofibrils (0.604 ± 0.029 µm/s SE, n = 28). (C) Native thin filaments purified from M. soleus were translocated significantly slower by M. soleus myosin (0.082 ± 0.004 µm/s SE, n = 21, T = 23°C) than by ventricular myosin (0.247 ± 0.016 µm/s SE, n = 21). (D) M. soleus myosin molecules moved cardiac thin filaments significantly slower (0.247 ± 0.009 µm/s SE, n = 19) than ventricular myosin molecules (0.604 ± 0.029 µm/s SE, n = 28). Data points represent mean gliding velocities of individual assay chambers, while bars represent mean values ± SE. Data could be described by normal distributions (intrinsic curves).