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

Abstract

Addition of certain chemical agents to the standard lactate dehydrogenase (LDH) incubating medium permits the histochemical display of selective LDH isozymes. On electrophoretic patterns, excess sodium lactate (0.72 to 1.41 M) decreases the intensity of the fast-moving isozymes, and urea (1.28 to 3.79 M) 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. Predominance of the slow-moving isozymes in guinea pig gastrocnemius and of the fast-moving isozymes in guinea pig soleus were observed on the electrophoretic patterns of the muscle extracts and then confirmed on the intact tissues by use of the modified incubating media. These media were also used to localize specific LDH isozymes in normal human muscle fibers. It was concluded that the slow-moving LDH isozymes predominate in the aqueous sarcoplasm of Type I (red) fibers while the fast-moving isozymes predominate in the aqueous sarcoplasm of Type II (white) 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.