Skeletal muscles of rabbits, chickens, frogs and fishes were studied by bright field, phase contrast and polarization microscopy after treatment with: (1) Alcian Blue, pH 2.5, (2) Alcian Blue, pH 1.0, (3) low iron diamine, (4) high iron diamine, (5) dialyzed iron, pH 2.0, and (6) colloidal iron, pH 1.5. A prominent aspect of each of the muscles studied was transverse muscle bands which stained with Alcian Blue at pH 2.5, low iron diamine and dialyzed and colloidal iron reagents. Staining of transverse bands was not very intense with these reagents, suggesting that the materials demonstrated occurred in relatively low concentrations. Staining of transverse bands in chicken, frog and fish muscles was observed also after treatment with Alcian Blue at pH 1.0 or with high iron diamine. Staining of rabbit muscle with Alcian Blue at pH 1.0 or with high iron diamine was not detectable even after the most effective fixatives employed in this study, viz., Carony's fixative or buffered HgCl2. Phase contrast and polarization microscopy indicated that the transverse bands stained by the reagents employed corresponded to the I bands in agreement with previous electron cytochemical studies of skeletal muscles treated with dialyzed iron at controlled pH. Methylation for 4 hr at 60°C prevented I band staining with Alcian Blue and dialyzed iron in each of the muscles studied. Treatment of muscle sections with Vibrio cholerae neuraminidase, testicular hyaluronidase or ribonuclease under optimal conditions did not prevent Alcian Blue staining of I bands. Trypsin treatment of muscle sections did not prevent I band staining except when digestion was prolonged to the point that muscle striations were no longer recognizable. Saponification prior to hyaluronidase treatment reduced I band staining in each of the muscles studied. Saponification alone and saponification prior to neuraminidase digestion left I band alcianophilia intact. It was concluded that myofibrillar I bands of rabbit, chicken, frog and fish skeletal muscles contain acid mucosubstances. It was suggested that in each of these organisms an esterified, hyaluronic acid-like molecule is present within the I bands. Sulfated mucosaccharides occur as additional components in the I bands of fish, chicken and frog skeletal muscles; sulfated mucosaccharides apparently are not present in rabbit muscle I bands. Available evidence indicates that sialomucins are not present in the myofibrils of the organisms studied. The possible functional significance of I band acid mucosubstances in vertebrate skeletal muscles was discussed.
CYTOCHEMICAL LOCALIZATION OF ACID MUCOSUBSTANCES WITHIN RABBIT, CHICKEN, FROG AND FISH SKELETAL MUSCLE FIBERS
