Molecular Insights into Excitation-Contraction Coupling
This extract was created in the absence of an abstract.
Excerpt
Excitation-contraction (E-C) coupling represents an essential feature of muscle function. In skeletal muscle, depolarization of transverse tubules (T tubules), infoldings of the cell-surface membrane, causes Ca++ to be released from the sarcoplasmic reticulum (SR) without requiring entry of extracellular Ca++ (Armstrong et al. 1972); the Ca++ released from the SR triggers contraction. One hypothesis for how skeletal muscle E-C coupling occurs is that a “voltage sensor” located in the T-tubular membrane is responsible for controlling the release of Ca++ from the SR (Schneider and Chandler 1973). Specifically, T-tubular depolarization induces a molecular rearrangement of the voltage sensor, which is postulated to gate calcium flow across the SR. Consistent with this hypothesis is the presence in skeletal muscle of voltage-dependent intramembrane charge movement (Schneider and Chandler 1973). The mechanism of depolarization-contraction coupling in cardiac muscle differs from that in skeletal muscle in that Ca++ influx across the sarcolemma is required for...
