Ligand binding and cooperative interactions among the subunits of the tetrameric Ca2+ release channel complex of sarcoplasmic reticulum.

Abstract

In skeletal muscle, rapid release of Ca2+ ions from the intracellular membrane compartment, sarcoplasmic reticulum, (SR) is triggered by a surface membrane action potential that is communicated to the SR at specialized areas where the “junctional” SR comes in close contact with the surface membrane and tubular infoldings of the surface membane (T-tubule); at these areas protein bridges are present which span the gap between the two membrane systems (Peachey and Franzini-Armstrong, 1983). These structures have been variously termed “feet” (Franzini-Armstrong, 1970), “bridges” (Somlyo, 1979), “pillars” (Eisenberg and Eisenberg, 1982) or “spanning proteins” (Caswell and Brandt, 1989) and are now believed to be identical with the ryanodine receptor or SR Ca2+ release channel (for reviews see Lai and Meissner, 1989; Fleischer and Inui, 1989).