A MORPHOLOGICAL AND CYTOCHEMICAL STUDY OF SARCOPLASMIC RETICULUM AND T SYSTEM OF FISH EXTRAOCULAR MUSCLE

The sarcolemma and T system and the sarcoplasmic reticulum were studied in a fast acting muscle, the extraocular muscle of Fundulus grandis. The predominant morphological fiber type contained abundant glycogen, a highly developed T system with triads at the A-I junction and a well developed sarcoplasmic reticulum. The numerous tubular profiles of T system and sarcoplasmic reticulum with their characteristic contents made this fiber especially suitable for cytochemical investigation. Revel's thorium dioxide technique for the ultrastructural localization of tissue polyanions was applied to thin sections of extraocular muscle. The results confirmed an earlier report by Goldstein and Philpott on fish branchial muscle. The polyanionic material was associated with the sarcolemma, the T system and the sarcoplasmic reticulum of these fibers. Both the distribution and the amount of polyanionic substance associated with these physiologically important membrane systems support the idea that the reactive material serves as an anionic substrate for binding cationic calcium. © 1969 Springer-Verlag.