Rods in the terminal cisternae of skeletal muscle

Abstract

The purpose of the study was to investigate rod-like structures (rods) in the terminal. Cisternae membrane of freeze fracture replicas of fast- and slow-twitch mammalian muscle. The 9 × 50 nm rods crossed the junctional gap perpendicular to the T-tubule membrane and terminated near indentations. Rods are likely to have a structural basis because (1) grooves were seen in the complimentary membrane leaflet, (2) rods were seen in tissue fixed in 0.5, 5, or 6% glutaraldehyde or 5% acrolein, (3) rods were seen in tissue fractured over a range of temperatures from −40 to −196°C, (4) the number of rods was correlated with the contractile properties of fibers, and (5) the density of rods increased when fibers were depolarized before fixation. The rods are in a unique location that would allow them to participate in excitation-contraction coupling, perhaps by transmitting an electrical signal from the T-tubule membrane to calcium release sites in the terminal cisternae.