CA2-FORCE RELATIONSHIP OF FROG SKELETAL-MUSCLE - A DYNAMIC-MODEL FOR PARAMETER-ESTIMATION()

A simple mathematical model describing the dynamic connection between Ca2+ and force generation in intact skeletal muscle from the frog has been developed from isometric force responses to cytosolic Ca2+ concen tration ([Ca2+](c)) transients during tetanic and twitch contractions. The main element of the model is a two-state cross-bridge cycle chara cterized by the fractional rate of cross-bridge attachment (f(app)) an d the fractional rate of cross-bridge detachment (g). While g* is con stant, f(app) is time varying and regulated by both [Ca2+](c) and forc e. Having only four adjustable parameters, the model is mathematically unique, thereby allowing precise parameter estimation from the dynami c Ca2+ and force data. The model should be useful for developing insig hts into the relative importance for force generation and relaxation o f 1) the size and shape of the Ca2+ transient, 2) the sensitivity of t he fractional rate of cross-bridge attachment to both the [Ca2+](c) an d the force responses, and 3) the fractional rate of cross-bridge deta chment, which is insensitive to both Ca2+ and force.