A silver-reducing component in rat striated muscle. I: Selective localization at the level of the terminal cistern/transverse tubule system. Light and electron microscope studies with a new histochemical procedure

This study reports the presence of a silver-reducing constituent in rat striated muscle fiber located selectively at the level of the terminal cistern/transverse tubule system. It is related to the T tubule network at or near sites that participate in junctions with terminal cisternae, i.e., at both sides of the T tubule in skeletal muscle (triad) and, predominantly, at one side in the ventricle (dyad). Little reactivity is present in the auricle due to the scarcity of those membrane systems. The longitudinal sarcoplasmic reticulum, the sarcolemma, mitochondria and myofibrils are not outlined by the reaction product. Extraction of low molecular weight substances, nucleic acids and lipids did not suppress the chemical reaction. A new argentaffin (Hg--Ag) technique is described. Ethanol or aldehyde fixed muscles were passed to water, postfixed 6-24 h with mercuric acetate (5% w/v in 1% acetic acid), washed with 1% acetic acid and distilled water, stained 12-24 h at 43 degrees C with ammoniacal silver nitrate (60% w/v) and washed in 10% sodium sulfite (three changes) and water. All steps were carried out in darkness. Postfixation with mercuric acetate proved to be essential for immobilizing the argentaffin component without interfering with its strong argentaffinity. The procedure also provides a simple method for tracing the pathway of transversally oriented membrane systems in skeletal and cardiac muscle cells.