Three-dimensional architecture of sarcoplasmic reticulum and T-system in human skeletal muscle.
A modified Golgi method combined with stereoscopy has been used to demonstrate the three-dimensional architecture of the sarcoplasmic reticulum (SR) and the T-system in human skeletal muscle. SR formed a continuous repeating network with a different structure dependent upon the sarcomere position. Intermyofibrillar SR contained three regions: 1) fenestrated collars overlying the M-band region, 2) terminal cisternae overlying the A-I region, and 3) a three-dimensional anastomosed tubular network overlying the Z-band region. Longitudinal and/or transverse SR tubules connected these regions. Subsarcolemmal SR was also composed of three regions: 1) transversely oriented polygonal meshes overlying the M-band, 2) single-layered tubules overlying the Z-band region, and 3) a loose network between the two. In the subsarcolemmal sarcoplasm, where mitochondria were aggregated, SR anastomosed loosely and showed nonfenestrated cisternae beneath the plasma membrane. The T-system was composed of transversely oriented networks overlying the A-I region with occasional longitudinal tubules connecting these networks.
D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D008297:Male; D008854:Microscopy, Electron; D008875:Middle Aged; D009132:Muscles / Q000648:ultrastructure*; D009210:Myofibrils / Q000648:ultrastructure; D012519:Sarcoplasmic Reticulum / Q000648:ultrastructure*; D013194:Staining and Labeling