Fig. 5

Relaxation process of smooth muscle. The fast cross-bridges (AM fast cycling) activated by Ca²⁺ dissociate once (A + M) with time constant (τ fast-detach) by lowering Ca²⁺ concentration. Then the dissociated myosin binds to actin, and forms slow cycling bridges (AM slow) with time constant (τ slow-attach), and then finally detaches (A + M) with time constant (τ slow-detach). The rate of re-attachment of the detached cross-bridges denotes A