Immunohistochemical Study Using Monoclonal Antibodies

To investigate the existence of heterogeneity of j-type myosin isozymes (HC,6) 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 HCQ (AI, and 2) was suggested in the atrium. By using affinity chromatography, two molecular variants ofHC# were isolated from the bovine atrium, and differences in the primary structure of 8 and 2 were confirmed by analysis of peptides produced by chymotriptic digestion. In pressure-overloaded human atria, myofibers containing fai and/or 2 increased in accordance with decrement of myofibers containing a-type myosin isozyme (P < 0.01). But they differed in expression during the developmental stage, since 2 did not exist in the early embryonic bovine heart, but t, did. Thus, there are two distinct HCQ whose expression is regulated by at least two factors: pressure overload and developmental stage.