Myosin isozymes in rabbit and human smooth muscles

Although multiple forms of myosin in cardiac and skeletal muscles have been identified, it has not been firmly established that myosin isozymes are present in adult smooth muscle. Myosin, extracted from human thoracic aorta and lower saphenous vein and rabbit aorta and uterus, was analyzed by pyrophosphate gel electrophoresis to determine if myosin isozymes are present in these tissues. In all smooth muscle tissues studied, two myosin isozymes were detected and labelled as smooth muscle 1 and smooth muscle 2, smooth muscle 2 being the faster migrating isozyme. Bovine cultured smooth muscle cells from the media of thoracic aorta also contained two forms of myosin. However, cultured fibroblasts contained only one form of myosin. Extracting myosin from either relaxed or contracting rabbit aortic smooth muscle did not influence the mobilities of smooth muscle 1 and smooth muscle 2 on pyrophosphate gels, suggesting that the degree of light chain phosphorylation did not significantly alter the electrophoretic mobility under our conditions. Smooth muscle 1 and smooth muscle 2 myosins each contain heavy chains (200,000 daltons) and light chains (20,000 and 17,000 daltons) in addition to filamin (235,000 daltons), which is closely associated with the native protein. Myosin peptide maps of rabbit aorta and uterus revealed areas of substantially different banding patterns between smooth muscle 1 and smooth muscle 2 from the same tissue. Similar peptide maps of smooth muscle 1 bands were produced from the different tissues, but the smooth muscle 2 maps were dissimilar.(ABSTRACT TRUNCATED AT 250 WORDS)