SDS-PAGE and Western blot analyses of native tissue purified ventricular and M. soleus myosin heavy and light chain composition. (A) 8% (top) and 6.5% (bottom) SDS-PAGE analyses of MyHCs in ventricular and M. soleus myosin. Rabbit M. psoas myosin containing mainly MyHC-IIb and atrial myosin containing both α- and β-MyHC served as references. No α-MyHC could be detected in myosin purified from ventricular tissue, while M. soleus myosin contained traces of MyHC-IIa (faint upper band). (B) 15% SDS-PAGE analysis of MLCs in atrial, ventricular, and M. soleus myosin preparations. Atrial myosin contained the ELC MLC1a and RLC MLC2a, while ventricular myosin contained ELC MLC1sb/v and RLC MLC2s/v. In addition to the latter two light chains, M. soleus myosin contained the ∼0.7 kD larger ELC MLC1sa. (C) Western blot analysis of MLCs in atrial and ventricular myosin preparations. Both atrial and ventricular ELCs MLC1a and MLC1s/v were immunolabeled by the antibody anti-MYL4 (top), and no signal of MLC1a was detected in ventricular myosin preparations. The atrial RLC (MLC2a) was labeled with an MLC2a specific antibody (bottom) and was absent in ventricular myosin samples. Source data are available for this figure: SourceData F3.