Uncontrolled sarcomere shortening increases the intracellular
calcium transient in rat cardiac trabeculae.
Janssen, Paul M. L., and Pieter P. De Tombe.
Section on Cardiology, Bowman Gray School of Medicine, Wake Forest
University, Winston-Salem, North Carolina 27157-1045
APStracts 3:0518H, 1996.
Isolated cardiac muscle preparations suffer from damaged-end
compliance that allows for substantial shortening of central
sarcomeres contractions in which the overall length of muscle is kept
constant. The impact of uncontrolled sarcomere shortening during a
twitch upon the intracellular calcium transient in myocardium is
unknown. Accordingly, in the present study we developed an iterative
laser diffraction feed-back system that allowed for the accurate
control of central segment sarcomere length and simultaneous
measurement of iontophoretically injected Fura-2 fluorescence in
isolated cardiac trabeculae. We compared Fura-2 fluorescence signals
recorded during regular twitches to twitches in which central
sarcomere length was held constant by feed-back control ("SL
clamp" twitches). We found that uncontrolled sarcomere
shortening was associated with a significant (p=0.005) increase in
the peak of the calcium transient, and that the amount of this
increase was directly correlated to the extent of central segment
sarcomere shortening (r2=0.92; p<0.01). The time-course of the
calcium transient, however, was unaffected by the mode of contraction
(p=0.64) . These findings have important implications for the
interpretation of studies on myocardial calcium handling in which
uncontrolled sarcomere shortening takes place during the twitch.
Received 30 July 1996; accepted in final form 6 November 1996.
APS Manuscript Number H691-6.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996