The SR of skeletal muscle: Its structure after quick-freezing and freeze-etching, following field stimulation of single intact muscle fibers

Abstract

It is known that the P faces of freeze-fractured SR of fixed and cryoprotected striated muscle fibers are studded with particles, whereas the E faces remain smooth, except for two staggered rows of pits in the junctional SR (JSR) which face transverse tubules (junctional pits). Freeze-fracture after quick-freezing of native skeletal muscle provides similar images (1). We have used freeze-etching to look at the SR's structure in single intact skeletal muscle fibers (r.temporaria) without stimulation, following varied post-stimulation intervals, and in tetanus. Single intact skeletal muscle fibers were isolated and quick-frozen as previously reported (2). After quick-freezing, the fibers were transferred to a Balzers 301 device and etched for 3 minutes at -100°C, followed by unidirectional Pt evaporation with an electron gun and carbon coating.