Fig. 1: Key players in skeletal muscle EC coupling: CaV1.1, Stac3 and RyR1.
From: The molecular transition that confers voltage dependence to muscle contraction
CaV1.1 channel macromolecular complex (α1S pore forming subunit (violet), auxiliary subunits β1a (yellow), α2δ−1 (green), and γ1 (black), and Stac3 adapter protein, orange) is thought to be in physical contact with RyR1 (gray). α1S comprises four concatenated repeats (I-IV), each of which includes a voltage-sensing domain (VSD, blue, red, green, and orange) and a quarter of the pore domain (enlargement). RyR1 is embedded in the SR membrane and cannot sense electrical signals in the sarcolemma directly; instead, it uses CaV1.1 voltage-sensing apparatus to gain voltage dependence. During an action potential, the voltage-dependent conformational rearrangements in one or more CaV1.1 VSD(s) are thought to propagate to RyR1, likely via the repeat II-III loop (red)50, which opens and releases Ca2+ from the sarcoplasmic reticulum (SR). (CaV1.1 Protein Data Bank ID 5GJV53, RyR1 Protein Data Bank ID 3J8H66).
