Characteristics of mitochondria isolated from type i and type iib
skeletal muscle.
Jackman, Matthew R., and Wayne T. Willis.
Exercise and Sport Research Institute, Arizona State University,
Tempe, AZ
APStracts 2:0322C, 1995.
Mitochondria isolated from rabbit soleus (98% type I) and gracilis
(99% type IIb) skeletal muscle were compared for compositional
differences. Whole muscle mitochondrial contents were 14.5 1.2 mg/g
of wet weight in soleus, and 5.3 0.6 mg/g in the gracilis muscle, a
2.7-fold difference. Maximal pyruvate + malate oxidase activity in
gracilis mitochondria was roughly 75% of that in soleus mitochondria.
In contrast, glycerol-3-phosphate (G-3-P) oxidation was 10-fold
greater in gracilis mitochondria. Both soleus and gracilis
mitochondria exhibited additive pyruvate and G-3-P oxidase
activities. In general, citric acid cycle enzyme activities were
higher in soleus mitochondria. A notable exception was isocitrate
dehydrogenase, which was 2-fold higher in gracilis mitochondria.
Substrate cytochrome-c reductase activities indicated that the
electron transport chain (ETC) of soleus mitochondria possess roughly
twice the capacity for both NADH and succinate oxidation. Similarly,
the maximal activities of NADH dehydrogenase and succinate
dehydrogenase were roughly 2-fold higher in soleus mitochondria. The
findings demonstrate that mitochondria isolated from types I and IIb
skeletal muscle differ substantially in composition. Furthermore, the
relatively similar pyruvate + malate oxidase activities in the face
of markedly different ETC capacities, suggest that the interaction
between matrix dehydrogenases and the ETC may differ in mitochondria
isolated from types I and IIb skeletal muscle.
Received 3 April 1995; accepted in final form 28 August 1995.
APS Manuscript Number C188-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 September 1995.