AJP - Endocrinology and Metabolism, Vol 258, Issue 1 E71-E77, Copyright © 1990 by American Physiological Society

ARTICLES

Endurance training, not acute exercise, differentially alters beta-receptors and cyclase in skeletal fiber types

P. J. Buckenmeyer, A. H. Goldfarb, J. S. Partilla, M. A. Pineyro and E. M. Dax
Department of Physical Education, University of Maryland, College Park 20742.

beta-Adrenergic receptor binding characteristics and adenylate cyclase activity were examined in rat skeletal muscle membranes to determine if acute exercise or endurance training altered beta-receptors or adenylate cyclase activity in different muscle fiber types. Binding characteristics and adenylate cyclase activity were examined in type IIA [red fast-twitch, red vastus (RV)], type IIB [white fast-twitch, white vastus (WV)], and type I [red slow-twitch, soleus (S)] muscles. Acute exercise involved a 20-min run on a treadmill at 20 m/min and did not alter beta-receptor density or adenylate cyclase activity in any of the fiber types examined. Endurance training consisted of a progressive treadmill protocol that involved increasing intensity and duration of exercise for 18 wk. beta-Adrenergic receptor density increased in skeletal muscle fiber types primarily recruited during submaximal training (types I and IIA), whereas nonreceptor-mediated adenylate cyclase activity was altered in the three fiber types. Endurance training significantly increased beta-receptor density in RV by 25% and in S by 19% (P less than 0.05), whereas in WV beta-receptor density was not altered. Basal adenylate cyclase activity in RV was increased approximately 2.5 fold by endurance training. Nonreceptor-mediated adenylate cyclase activity, stimulated by NaF and forskolin, increased by approximately twofold in both RV and WV as a result of endurance training. The data support and extend previous observations to show greater effects of endurance training in types I and IIA fibers with respect to alterations in beta-receptor density and alterations in adenylate cyclase activity in each fiber type. Acute exercise did not alter these parameters either in trained or untrained rats.

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