IMMUNOHISTOCHEMICAL DIFFERENTIATION OF FIBER TYPES IN HUMAN SKELETAL-MUSCLE USING MONOCLONAL-ANTIBODIES TO SLOW AND FAST ISOFORMS OF TROPONIN-I SUBUNIT

The cDNA sequence of troponin I (TnI), one of the subunits of the skel etal muscle regulatory protein, differs between slow-twitch muscle and fast-twitch muscle. We prepared monoclonal antibodies to the slow and fast isoforms of human TnI for the purpose of differentiating muscle fiber types :in human neuromuscular disorders. Slow TnI antibody was l abeled with tetramethylrhodamine isothiocyanate while fast TnI antibod y was labeled with fluorescein isothiocyanate; then these two antibodi es were mixed, This mixture was then used to stain biopsied muscle fro m patients with neuromuscular disorders. It was possible to differenti ate muscle fibers into slow, fast and intermediate fibers having vario us contents of slow and fast TnI, In tissue composed of small muscle f ibers, this method facilitated differentiation of types of muscle fibe rs by allowing staining of only a single section, The usefulness of ou r technique using slow and fast TnI antibodies is discussed in compari son with ATPase staining, Because our staining method can distinguish slow and fast fiber components, it is useful for clinical application.