AJP - Heart and Circulatory Physiology, Vol 251, Issue 5 941-H948, Copyright © 1986 by American Physiological Society
Muscle mechanics and Ca2+ transport in atrophic heart transplants in rat
B. Korecky, P. K. Ganguly, V. Elimban and N. S. Dhalla
Isometric contractile activity and force-frequency relationship were
investigated in heterotopically isotransplanted rat hearts that performed
minimal external work for 8 wk and underwent atrophy. No changes were found
in the isometric contraction phase of the papillary muscles from the
transplants when compared with the hearts of recipient animals that carry
full hemodynamic load. However, the relaxation phase of the transplants was
impaired at higher frequencies (greater than 24 stimuli/min) of stimulation
and at higher levels of calcium (greater than 2.0 mM Ca2+) in the medium.
When Ca2+-accumulating activities of cardiac microsomes containing
fragments of the sarcoplasmic reticulum (SR) were studied, a significant
decrease was seen in the transplanted hearts in comparison with the host
hearts. This decrease in Ca2+-uptake activity was observed at different
times of incubation as well as different concentrations of free Ca2+
(10(-7) to 10(-5) M Ca2+). Although Ca2+-stimulated ATPase activity did not
change, alterations in the phospholipid contents of the SR vesicles from
the transplanted hearts were observed. These results provide some evidence
for a depression in the SR Ca2+ uptake in transplanted hearts undergoing
atrophy and may explain the underlying alteration in the relaxation phase
of these hearts.
