Heterogeneity of beta-type myosin isozymes in the human heart and regulational mechanisms in their expression. Immunohistochemical study using monoclonal antibodies.

To investigate the existence of heterogeneity of beta-type myosin isozymes (HC beta) in human hearts, immunohistochemical studies using monoclonal antibodies (MoAbs) raised against human ventricular myosin heavy chains were performed. Two types of MoAbs recognized some muscle fibers in the atrium, whereas both reacted with all ventricular muscle fibers. Since atrial muscle fibers reactive with each MoAb were found to be clearly different, the existence of two immunologically distinct HC beta (beta 1, and beta 2) was suggested in the atrium. By using affinity chromatography, two molecular variants of HC beta were isolated from the bovine atrium, and differences in the primary structure of beta 1 and beta 2 were confirmed by analysis of peptides produced by chymotryptic digestion. In pressure-overloaded human atria, myofibers containing beta 1 and/or beta 2 increased in accordance with decrement of myofibers containing alpha-type myosin isozyme (P less than 0.01). But they differed in expression during the developmental stage, since beta 2 did not exist in the early embryonic bovine heart, but beta 1 did. Thus, there are two distinct HC beta whose expression is regulated by at least two factors: pressure overload and developmental stage.