AJP - Cell Physiology, Vol 271, Issue 6 C2062-C2071, Copyright © 1996 by American Physiological Society
Ca(2+)-force relationship of frog skeletal muscle: a dynamic model for parameter estimation
D. M. Shames, A. J. Baker, M. W. Weiner and S. A. Camacho
Department of Medicine (Cardiology), University of California, San Francisco 94143, USA.
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+ concentration
([Ca2+]c) transients during tetanic and twitch contractions. The main
element of the model is a two-state cross-bridge cycle characterized by the
fractional rate of cross-bridge attachment (f(app)) and the fractional rate
of cross-bridge detachment (g*). While g* is constant, f(app) is time
varying and regulated by both [Ca2+]c and force. Having only four
adjustable parameters, the model is mathematically unique, thereby allowing
precise parameter estimation from the dynamic Ca2+ and force data. The
model should be useful for developing insights into the relative importance
for force generation and relaxation of 1) the size and shape of the Ca2+
transient, 2) the sensitivity of the fractional rate of cross-bridge
attachment to both the [Ca2+]c and the force responses, and 3) the
fractional rate of cross-bridge detachment, which is insensitive to both
Ca2+ and force.
