3-DIMENSIONAL STRUCTURE OF THE SARCOPLASMIC-RETICULUM AT THE NEUROMUSCULAR-JUNCTIONS OF THE RAT DIAPHRAGM

The three-dimensional structure of the sarcoplasmic reticulum at the n euromuscular junctions of the rat diaphragm was investigated by means of a selective staining technique allowing studies of thick sections c ombined with stereoscopic observations. The sarcoplasmic reticulum (SR ) has different organizations related to the various regions of the po stsynaptic cytoplasm. At the base of the membranous folds or deep regi on, flattened cisternae are smaller and connected by numerous anastomo sed tubules. In the mitochondria-rich region, the SR is composed of la rge flattened cisternae. Between the postsynaptic folds, the SR is for med of poorly anastomosed thin tubes which give rise to single tubules running close to the plasmalemma. The SR is also associated with the Golgi apparatus present in the deeper mitochondria-rich region. This s pecific organization of the SR in the postsynaptic cytoplasm of the ne uromuscular junctions might, like the Golgi apparatus, be involved in the synthesis of some specific proteins, enzymes and receptors.