Toward the ultimate skeletal model

Abstract

Huxley was OK either for frog at 0 deg, or for frog at 20 deg, but not both together. Problems with shortening heat, which is monotonic in reality but not in the model. So search for improvements, initially trying to account only for isometric data. Cross co-operativity is the most important factor: a formed cross-bridge can expose adjacent binding sites. It is needed to account for the steepness of the force-stimulation curve. Co-operativity also causes the force produced by high frequencies of stimulation to linger (an effect much reduced if the muscel chnages length). By lumping non-rate-limiting steps, come out with a two state crossbridge model and a two-state Ca model. Zahalek no faster than Huxley with 20-40 bins, but can get by with rectangular rather than Gaussian distributions for Zahalek, which is much faster. NB isometric does in fact have 1% shortening: it appears that shortening velocity has a big effect on detachment rates.