Histochemical detection of specific isozymes of myosin in rat ventricular cells.

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 V1 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, V1 and V3. The technique is capable of detecting as small a change in the relative amount of V1 as 15% of the total myosin. Isoenzymes appear to be uniformly distributed within each ventricular cell. There is only a small difference in the content of V1 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 V1 concentration among the cells. The functional implications of the mixture of isozymes is discussed.