AJP - Heart and Circulatory Physiology, Vol 258, Issue 5 1482-H1490, Copyright © 1990 by American Physiological Society
Role of cardiac work in regulating myocardial biochemical characteristics
L. Hornby, N. Hamilton, D. Marshall, T. A. Salerno, M. H. Laughlin and C. D. Ianuzzo
Department of Physical Education, Faculty of Science, York University, Downsview, Ontario, Canada.
The purpose of this study was to determine the extent to which functional
demand regulates the biochemical character and enzyme capacities of the rat
myocardium. Hearts from donor rats were heterotopically transplanted onto
the abdominal aorta and inferior vena cava of isogenic recipients. The
procedure results in a perfused but nonpumping heart that has a reduced
heart rate (HR) and performs essentially no stroke work (SW). After 30
days, metabolic enzyme activities (phosphorylase, 6-phosphofructokinase,
citrate synthase, and 3-hydroxyacyl-CoA dehydrogenase) were significantly
lower (40-60%) in the nonworking heart. Specific sarcoplasmic reticulum
Ca2(+)-adenosinetriphosphatase (ATPase) activity was unchanged, but
activity per gram of heart was 41% lower. Myosin isozymes were 58% V1, 21%
V2, and 21% V3 in the nonworking heart compared with 100% V1 in the working
heart. Myosin and myofibrillar ATPase activities each decreased by 28%.
These findings suggest that both HR and SW play major and specific roles in
regulating myocardial biochemical capacities and determining the myosin
phenotype.
