Journal of Applied Physiology
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J Appl Physiol 66: 2017-2022, 1989;
8750-7587/89 $5.00
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Journal of Applied Physiology, Vol 66, Issue 5 2017-2022, Copyright © 1989 by American Physiological Society

ARTICLES

Isoproterenol attenuates myosin phosphorylation and contraction of tracheal muscle

K. Obara and P. de Lanerolle
Department of Physiology and Biophysics, College of Medicine, University of Illinois, Chicago 60612.

The effects of isoproterenol on isometric force, unloaded shortening velocity, and myosin phosphorylation were examined in thin muscle bundles (0.1-0.2 mm diam) dissected from lamb tracheal smooth muscle. Methacholine (10(-6) M) induced rapid increases in isometric force and in phosphorylation of the 20,000-Da myosin light chain. Myosin phosphorylation remained elevated during steady-state maintenance of isometric force. The shortening velocity peaked at 15 s after stimulation with methacholine and then declined to approximately 45% of the maximal value by 3 min. Isoproterenol pretreatment inhibited methacholine-stimulated myosin light chain phosphorylation, shortening velocity, and force during the early stages of force generation. However, the inhibitory effect of isoproterenol on force and myosin phosphorylation is proportionally greater than that on shortening velocity. Isoproterenol pretreatment also caused a rightward non-parallel shift in the methacholine dose-response curves for both isometric tension and myosin light chain phosphorylation. These data demonstrate that isoproterenol attenuates the contractile properties of airway smooth muscles by affecting the rate and extent of myosin light chain phosphorylation, perhaps through a mechanism that involves the synergistic interaction of myosin light chain kinase phosphorylation and Ca2+ metabolism.


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 Am. J. Physiol. Lung Cell. Mol. Physiol.Home page
T. L. Croxton, B. Lande, and C. A. Hirshman
Role of G proteins in agonist-induced Ca2+ sensitization of tracheal smooth muscle
Am J Physiol Lung Cell Mol Physiol, October 1, 1998; 275(4): L748 - L755.
[Abstract] [Full Text] [PDF]


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