Rabbit psoas skeletal muscle fibers were held at constant length and rigor induced by immersion in glycerol. The fibers were quick-frozen by contact with a liquid helium- cooled copper block in a Heuser-type cryopress, and freeze-etched in a Balzers 400 freeze fracture machine. The sample was then rotary-replicated with Pt-C at 24 degrees and visualized in a JEOL 100CX2 transmission electron microscope operated at 100 kev. Images were recorded on Kodak 4489 film at 68,000x magnification. Stereo pairs were taken at +5 and -5 degrees. Films were scanned with a 20 micrometer pixel spacing on a Nikon Coolscan 9000ED scanner.
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