title: Ultra-high-resolution scanning electron microscopy of the sarcoplasmic reticulum of the rat atrial myocardial cells.
abstract: The sarcoplasmic reticulum (SR) of mammalian ventricular and atrial muscles share common features but also differ because T-tubules are rare and extended junctional SR is exclusively seen in the atrium. This scanning electron microscope (SEM) study was undertaken to clarify the three-dimensional organization of the rat atrial SR system. Specific preparations were examined with an ultra-high-resolution SEM.
  
  
  
  Fixed right rat atria were frozen, fractured, and macerated by the aldehyde-osmium-DMSO-osmium method to remove myofibrils and cytoplasmic matrix. Left exposed were mitochondria, SR, and sarcolemma. Dried specimens were then impregnated by osmium-hydrazine and examined without metal coating.
  
  
  
  In place of conventional T-tubules, a prominent type of sarcotubules, Z-tubules, were found at the Z-line level. Branches from these tubules joined the cisternal SR, which was 100-300 nm in diameter and localized near the Z-line, and formed extensive SR meshworks and polygonal patches. Bulbous swellings, the corbular SR, were also evident. Sarcotubular reticulum completely surrounded each myofibril. The intermyofibrillar SR, especially Z-tubules, joined the peripheral subsarcolemmal SR, which was also arranged as a meshwork and was closely apposed to the sarcolemma.
  
  
  
  These SEM observations confirm the organization of the rat atrial SR system and present new, detailed, three-dimensional images of Z-tubules, cisternal SR, extended junctional SR, and peripheral SR, which provide further structural insight.
authors.affiliation: Department of Surgery, Kochi Medical School, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Yamasaki
authors.forename: Y
authors.initials: Y
authors.lastname: Furuya
authors.forename: K
authors.initials: K
authors.lastname: Araki
authors.forename: K
authors.initials: K
authors.lastname: Matsuura
authors.forename: M
authors.initials: M
authors.lastname: Kobayashi
authors.forename: T
authors.initials: T
authors.lastname: Ogata
mesh_terms: D000818:Animals; D006325:Heart Atria / Q000648:ultrastructure; D008297:Male; D008855:Microscopy, Electron, Scanning / Q000379:methods*; D009206:Myocardium / Q000648:ultrastructure*; D051381:Rats; D017208:Rats, Wistar; D012508:Sarcolemma / Q000648:ultrastructure; D012519:Sarcoplasmic Reticulum / Q000648:ultrastructure*; D016707:Tissue Fixation / Q000379:methods