Stepwise changes in crossbridge state and sarcomere length: do lattice constraints play a critical role?

Observed abrupt and stepwise changes in crossbridge state induced by MgPPi in skeletal fibers using spin label techniques as well as stepwise changes in sarcomere length in actively contracting fibers are considered in terms of a model based on the principles of catastrophe theory and nucleation of structural transitions in mechanically constrained polymeric assemblies.