Functions of Stretch Activation in Heart Muscle

Stretch activation is an intrinsic length-sensing mechanism that allows muscle to function with an autonomous regulation that reduces reliance on extrinsic regulatory systems. This autonomous regulation is most dramatic in asynchronous insect flight muscle and gives rise to wing beat frequencies that exceed the frequency capacity of neural motor control systems. Stretch activation in insect flight muscle allows the contractile features of the flight muscle to be matched and tuned to the wing-thorax-aerodynamic load to ensure proper muscle contraction frequency and effort for flight (Pringle, 1977); a role for which intrinsic autonomous regulation is especially suited. In stretch-sensitive insect flight muscles, neurally controlled intracellular calcium plays a permissive role (it needs to be present at adequate levels to allow the intrinsic stretch activation mechanisms to operate) but it is not the dominant player in force generation or in work production. That role belongs to stretch...