Parvalbumin relaxes frog skeletal muscle when the sarcoplasmic
reticulum ca-atpase is inhibited.
Jiang, Y., J. David Johnson, and Jack A. Rall.
Departments of Physiology and Medical Biochemistry, Ohio State
University, Columbus, Ohio 43210
APStracts 2:0294C, 1995.
Inhibition of sarcoplasmic reticulum (SR) Ca-ATPase with 2,5-di(tert
-butyl)-1,4-benzohydroquinone (TBQ) in frog skeletal muscle fibers at
10 oC prolonged the half-time of the fall of the Ca2+ transient by
62% and of twitch force by 100% and increased peak force by 120%
without increasing the amplitude of the Ca2+ signal. In the presence
of TBQ the rate of relaxation and the rate of fall of Ca2+ became
progressively slower in a series of twitches until relaxation failed.
Relaxation rate decreased with a time course (2 s-1) which was
similar to the Mg2+ off rate from purified parvalbumin (PA) (3.6 s
-1). TBQ slowed the rate of fall of Ca2+ (5 fold) and of force (8
fold) in a 0.3 s tetanus such that the rate of fall of Ca2+ (2.5 s-1)
was similar to the Mg2+ off rate from PA. TBQ caused a near total
failure of both Ca2+ sequestration and relaxation in a 1.1 s tetanus
where PA would be saturated with Ca2+ and could not contribute to
relaxation. Thus when the SR Ca-ATPase is inhibited, Mg x PA can
sequester Ca2+ and produce relaxation at a rate which is defined by
the Mg2+ off rate from PA.
Received 12 December 1994; accepted in final form 2 August 1995.
APS Manuscript Number C713-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 14 August 1995.