Sarcoplasmic reticulum in cardiac length-dependent activation in
rabbits.
Bluhm, Wolfgang F., and Wilbur Y. W. Lew.
Departments of Bioengineering and Medicine (Cardiology), The
University of California, San Diego, La Jolla, California 92093-0412
and Cardiology Division, Department of Veterans Affairs Medical
Center, San Diego, California 92161
APStracts 2:0106H, 1995.
After a step increase in length of rabbit right ventricular papillary
muscles, active stress increased immediately followed by a further
slow increase in stress over 15 to 20 minutes. We studied the
contribution of the sarcoplasmic reticulum (SR) to the slow change in
stress (SCS) after changing muscle length from 85 % to 95 % of Lmax.
The SCS amounted to 32.5 +/- 12.2 % (mean +/- SD, n=19) of the total
increase in active stress. This was associated with a 13.2 +/- 8.7 %
increase in calcium content of the SR as estimated with rapid cooling
contractures (p<0.0001, n=19). However, SCS was not dependent on SR
calcium content. There was no significant attenuation in SCS after SR
calcium depletion with ryanodine (n=6), SR Ca-ATPase inhibition with
cyclopiazonic acid (n=6), or combined treatment with ryanodine and
cyclopiazonic acid (n=3). We conclude that in the rabbit, SR calcium
content increases slowly following a step increase in cardiac muscle
length, but the slow changes in active stress are not dependent on
the sarcoplasmic reticulum.
Received 11 August 1994; accepted in final form 17 March 1995.
APS Manuscript Number H716-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 4 April 1995.