Biochemical interpretation of tension transients produced by a four-state mechanical model.

We have simulated transient tension responses seen in rabbit psoas and insect flight muscle using a four-state cycle. A wide range of all the rate constants in the cycle and a minimum number of simple mechanical assumptions were used. The rate constants were noted for those cases in which the transient resembled a response seen in real muscle and in which the values of ATP turnover were realistic. The rate constants fell within narrow ranges. With a suitable correspondence of mechanical and biochemical state the actual rate constants were compatible with those determined in biochemical experiments. It was possible to model the effects of temperature, calcium ion concentration, length change and the removal of inorganic phosphate.