Distribution of myosin isozymes in human atrial and ventricular myocardium: Comparison in normal and overloaded heart

We have prepared monoclonal antibodies specific for either atrial or ventricular myosin and defined the isomyosin composition of myocardium in normal and overloaded human hearts. In the atrial myocardium, normal isozymic pattern was V₁ dominant which converted to being V₃ dominant in an overloaded condition. In contrast, normal isomyosin pattern of the ventricular myocardium was exclusively V₃ dominant, and only a small change in the proportion of isomyosin was observed in an overloaded condition. From this, we conclude that isozymic changes in cardiac myosin could occur in the human heart to meet increased work induced by cardiac overload. However, the physiological importance of these isomyosin redistributions in human myocardium seems to be much greater in the atrium than in the ventricle, since larger amounts of V₁ isomyosin which could be transformed to V₃ isomyosin were present in the atrial myocardium.