BRIEF COMMUNICATIONS Histochemical Detection of Specific Isozymes of Myosin

SUMMARY. A histochemical method for distinguishing isozymes of myosin in rat ventricles has been developed. The procedure involves preincubation in pH 10.5, which inhibits Ca-activated ATPase of the V3 isozyme but not the Vi isozyme of myosin. The specificity of the technique has been demonstrated by comparison of results in hearts from young euthyroid and hypothyroid rats, in which the predominant isozymes are, respectively, Vi and V3. The technique is capable of detecting as small a change in the relative amount of Vi as 15 % of the total myosin. Isozymes appear to be uniformly distributed within each ventricular cell. There is only a small difference in the content of Vi among the cells in a ventricular chamber of hearts from young euthyroid and hypothyroid rats, but in the period of rapid transition of isozyme content after thyroidectomy, there is considerable heterogeneity of Vi concentration among the cells. The functional implications of the mixture of isozymes is discussed. (Circ Res 51: 802-809, 1982) VENTRICLES of mammalian hearts can contain more than one type of myosin. In their very important study of rat ventricle, Hoh et al. (1977) found three isozymes of myosin that differed structurally in thei