Isolation and characterization of two beta-type cardiac myosin in the canine atrium.

Recently, we demonstrated that more beta-type myosin heavy chain (HC) was expressed in the overloaded atrium, and that there were 2 structurally different beta-type myosin heavy chains in the bovine heart. To determine the existence of the 2 beta-type HC in other animals and to clarify the characteristics of these beta-type HCs, we produced tricuspid regurgitation and pulmonary stenosis in the canine heart, and performed an immunological study using 3 monoclonal antibodies, 2 beta-type specific antibodies (HMC14 and 50) and 1 alpha-type specific antibody (CMA19). In an immunohistochemical study, serial cryostat sections revealed that some myofibers reacted with HMC50 (HC beta 2), but almost no fibers were labeled with HMC14 in the normal atrium. However, in overloaded atria, not only HC beta 2 but the HC, reacted with HMC14 (HC beta 1). By affinity chromatography, HC beta 2 was fractionated from normal atrial myosin using HMC50 and HC beta 1 was fractionated from overloaded atrial myosin using HMC14. These 2 HC beta's were subjected to digestion by alpha-chymotrypsin, staphylococcus aureus V8 protease, and cyanogen bromide, and proved to have different peptide fragments. In respect to enzymatic properties, the Ca2+-activated ATPase activities of HC beta 1 and beta 2 were almost the same but lower than that of HC alpha. We concluded that the isozymic transition of HC alpha to HC beta in the atrium was experimentally induced by hemodynamic overload and that HC beta 1, which was hardly recognized in the normal atrium but highly induced by overload, was structurally different from HC beta 2, as expressed in the normal atrium.