ISOZYME HISTOCHEMISTRY: THE DISPLAY OF SELECTIVE LACTATE DEHYDROGENASE ISOZYMES IN SECTIONS OF SKELETAL MUSCLE

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Abstract
The addition of chemical agents to the standard lactate dehydrogenase (LDH) incubating medium permits the histochemical display of selective LDH isozymes. Excess lactate decreases the intensity of the fast-moving isozymes, and urea decreases the intensity of the slow-moving isozymes. Application of these modified incubating media to histologic sections allows the display of selective LDH isozymes in unhomogenized tissues. Thus, predominance of the slow-moving LDH isozymes in guinea pig gastroenemius and of the fast-moving isozymes in guinea pig soleus were found on the electrophoretic patterns of the muscle extracts and confirmed on the intact tissues. The modified incubating media were used to localize specific LDH isozymes in normal human skeletal muscle. Ry extraction of the sections with saline or acetone the intracellular sites of isozyme activity were identified with recognized cell constituents. It was concluded that the slow-moving LDH isozymes predominate in the aqueous sarcoplasm of Type I fibers while the fast-moving isozymes predominate in the aqueous sarcoplasm of Type II fibers and in the mitochondria and lipid-mitochondrial complexes. The Pattern of dark and light fibers, seen after incubation in the standard LDH medium, was found to be due to the greater activity of the slow-moving isozymes in the Type I than the Type II fibers. Thus technique of isozyme histochemistry thus allows study of the intracellular localizations and the biochemical roles of specific LDH isozymes in skeletal muscles.