Calcium model for mammalian skeletal muscle

A model is presented describing quantitatively the events between excitation and force development in skeletal muscle. It consists of a calcium mediated activation model (c.m.a.m.) in series with a force generator model (f.g.m.). The c.m.a.m. was based on intracellular processes such as cisternal Ca-release, Ca-troponin interaction and Ca-uptake by SR. Ca-troponin complex concentration is an output of the c.m.a.m. and input of the f.g.m., the latter being a simplified actinmyosin cross-bridge model. Simulated and measured forces were compared for the rat slow (soleus) muscle. With the present structure and parameter values there is reasonable agreement between simulated and measured forces for single- and double-pulse responses. The parameters of the f.g.m. mainly determine the rising phase of the twitch since the Ca-release is brief and the binding of Ca to troponin is fast. In relaxation the Ca-troponin interaction and the Ca transporting ATPase parameters are also important. The behaviour of the muscle after a second action potential depends strongly on the level of Ca occupancy for both the troponin and Ca transporting ATPase.