THE LOCATION OF SODIUM IN THE TRANSVERSE TUBULES OF SKELETAL MUSCLE

Abstract

The location of Na was studied by electron microscopy in the frog sartorius muscles fixed in a glutaraldehyde medium containing KSb (OH)g and postfixed in osmium tetroxide. A dense precipitate of sodium pyroantimonate only was observed inside the transverse tubules of the T system, whereas the sarcoplasmic reticulum and interfibrillar areas were completely free of the precipitate. The outer region of the sarcolemma showed profuse precipitate. The fluid inside the transverse tubules probably has a high or higher concentration of Na than the rest of the muscle fiber which indicates the communication of these tubules with the extracellular space. However, there is a possibility that the reagent utilized did not penetrate the plasma membrane of the muscle fibers.