The Fine Structural Differences in Human Muscle Fiber Types Based on Peroxidatic Activity

Abstract

In normal human skeletal muscle stained with diaminobenzidine (DAB) two distinct fiber types were identified. The DAB staining persisted after fixation in glutaraldehyde and formalin. The fibers “rich” (dark) in DAB were the same as type I fibers in both regular myofibrillar ATPase (pH 9.4) and NADH-TR stains and the DAB “poor” (light) fibers correlated with type II fibers. In muscle fixed in glutaraldehyde and prepared for electron microscopy, DAB staining was done during processing permitting identification of type I and type II fibers in one micron thick sections of epoxy resin embedded material. When these fibers were identified in the electron microscope they showed consistent differences in fine structure: type I fibers had wider Z-bands (1211 Å diameter) compared to type II fibers (812 Å diameter); the number of mitochondria per micron² A-band area was 0.839 for type I fibers compared to 0.549 for type II fibers; and the number of lipid droplets per micron² A-band area was 0.070 for type I fibers and 0.010 for type II fibers.