Composition and size of type i, iia, iid/x, and iib fibers and
citrate synthase activity of rat skeletal muscle.
Delp, Michael D., Changping Duan.
Departments of Health and Kinesiology and Medical Physiology, Texas
A&M University, College Station, Texas 77843-4243, and Department
of Surgery, Cardiovascular and Pulmonary Research Center, Allegheny
-Singer Research Institute, Pittsburgh, PA 15212
APStracts 2:0378A, 1995.
A population of muscle fibers containing a myosin heavy chain isoform
IId (or 2x) has recently been identified in rat muscle. The purpose
of this study was to histochemically determine the relative
population and size of muscle fibers composed of type IID/X fibers,
as well as type I, IIA, and IIB fibers, in order to estimate the
absolute mass of the different types of fibers in rat muscle. In
addition, muscle citrate synthase activity was measured to determine
the relationship between fiber composition and muscle oxidative
capacity. Seventy-six muscles or muscle parts from the face, neck,
shoulder, arm, trunk, hip, thigh, and leg of three adult (4.5-5
months of age) male Sprague-Dawley rats were removed, weighed, and
frozen for histochemical and biochemical analysis. The data
demonstrated that type IIB fibers make up 71% of the total muscle
mass, type IID/X fibers 18%, type IIA fibers 5%, and type I fibers
6%. The mean cross-sectional area across all muscles for type IIB
fibers was 5,078 +/- 175 [mu]m2, 3,078 +/- 105 [mu]m2 for type IID/X
fibers, 2,045 +/- 80 [mu]m2 for type IIA fibers, and 1,898 +/- 90
[mu]m2 for type I fibers. Citrate synthase activity, an indicator of
muscle mitochondrial content, was most closely related to the
population of type IIA fibers, and was in the rank order of type IIA
> I > IID/X > IIB. NADH-TR staining intensity also
confirmed this order. These data demonstrate that type IID/X fibers
make up a significant portion of the adult rat muscle mass, and are
intermediate to type IIA and IIB fibers in regard to fiber size and
oxidative potential.
Received 24 April 1995; accepted in final form 17 August 1995.
APS Manuscript Number A438-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 15 September 1995.