Constancy and variability of contractile efficiency as a function
of calcium and crossbridge kinetics: simulation.
Yamaguchi, Hiroki, Miyako Takaki, Hiromi Matsubara, Shingo Yasuhara,
and Hiroyuki Suga.
Department of Physiology II, Okayama University Medical School,
Shikatacho, Okayama, 700 JAPAN
APStracts 2:0444H, 1995.
We simulated myocardial Ca2+ (Ca) and crossbridge (CB) kinetics to get
insight into the experimentally observed constancy and variability of
cardiac "contractile efficiency" in generating "total
mechanical energy" under various inotropic and pathological
conditions. The simulation consisted of a Ca transient, Ca
association and dissociation rate constants of troponin C, and CB on
and off rate constants. We evaluated sarcomere-isometric twitch
contractions at a constant muscle length. We assumed that each CB
cycle hydrolyzes one ATP and that the "force-length area"
(FLA) quantifies the total mechanical energy generated by CB cycles
in a twitch contraction. FLA is a linear version of the
"pressure-volume area" (PVA) which quantifies the total
mechanical energy of cardiac twitch contraction and correlates
linearly with cardiac oxygen consumption (Suga: Ventricular
energetics. Physiol Rev 70: 247-277, 1990). The simulation shows that
the contractile efficiency varies with changes in the Ca transient
and Ca and CB kinetics except when they simultaneously speed up or
slow down proportionally. These results point to possible mechanisms
underlying the constancy and variability of cardiac contractile
efficiency.
Received 22 June 1994; accepted in final form 22 September 1995.
APS Manuscript Number H550-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95