Journal of Applied Physiology, Vol 72, Issue 1 266-271, Copyright © 1992 by American Physiological Society
Effect of chronic respiratory load on cytochrome oxidase activity in diaphragmatic fibers
A. R. Bazzy and Y. J. Kim
Department of Pediatrics, Yale University School of Medicine, New Haven, Connecticut 06510.
To determine whether the increase in oxidative capacity after respiratory
muscle training with chronic inspiratory loads in sheep is specific to a
particular fiber type, we measured cytochrome c oxidase (COX) activity in
type I and type II fibers. COX activity in individual fibers was examined
histochemically and measured as relative optical density by use of an image
processing system. Fiber types were differentiated by the myosin
adenosine-triphosphatase reaction. We found that COX activity was higher in
both fiber types in the trained diaphragms than in the control diaphragms
(P less than 0.01). The increase with training was greater in type II (39%)
than in type I fibers (21%), resulting in relatively homogeneous COX
activity in all diaphragmatic fibers. The proportion of type I fibers
increased from 43.4 +/- 5.4% in the control diaphragm to 53.1 +/- 2.9% in
the trained diaphragm, whereas the proportion of type II fibers decreased
(P less than 0.001). We conclude that respiratory muscle training activates
oxidative enzyme activity in both diaphragmatic fiber types; this
activation is differentially more in type II fibers, which also decrease in
proportion, and less in type I fibers, which increase in proportion.
