Calcium removal kinetics of the sarcoplasmic reticulum atpase in
skeletal muscle.
Getz, Elise E. Burmeister, and Steven L. Lehman.
Department of Biochemistry and Biophysics, University of
California, San Francisco, California, 94143, Department of Human
Biodynamics, University of California, Berkeley, California 94720 and
UCB/UCSF Bioengineering Graduate Group, University of California,
Berkeley, California 94720 and San Francisco, California, 94143
APStracts 3:0355C, 1996.
The models of the sarcoplasmic reticulum (SR) calcium (Ca) pump
presently used to simulate Ca kinetics in muscle fibers are simple,
but inconsistent with data on Ca binding or steady-state uptake. This
paper develops a model of the SR pump that is consistent with data on
both transient and steady-state Ca removal, and has rate constants
identified under near-physiological conditions. The paper also
develops models of the other main Ca binding proteins in skeletal
muscle, troponin-C and parvalbumin. These models are used to simulate
Ca transients in cut fibers, during and after depolarizing pulses.
Simulations using the full SR pump model are contrasted with
simulations using a Michaelis-Menten (MM) approximation to SR pump
kinetics. The MM pump underestimates the amount of Ca released during
depolarization, underestimates the initial rate of Ca binding by the
pump, and overestimates the later rate of Ca pumping. These errors
are due to fast initial binding by the SR pump, which is neglected in
the MM approximation.
Received 24 July 1996; accepted in final form 16 October 1996.
APS Manuscript Number C413-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 November 1996