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Am J Physiol Cell Physiol 256: C315-C321, 1989;
0363-6143/89 $5.00
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AJP - Cell Physiology, Vol 256, Issue 2 C315-C321, Copyright © 1989 by American Physiological Society

ARTICLES

Myosin dephosphorylation during rapid relaxation of hog carotid artery smooth muscle

S. P. Driska, P. G. Stein and R. Porter
Department of Physiology, School of Medicine, Temple University, Philadelphia, Pennsylvania 19140.

Changes in myosin light chain phosphorylation were measured during histamine-induced rhythmic contractions of hog carotid artery smooth muscle strips. Histamine made the muscle strips contract spontaneously every 1-5 min, and this allowed measurement of the time course of phosphorylation in relation to force development under conditions where diffusion of the agonist through tissue would not complicate the interpretation of the data. In the absence of histamine, phosphorylation was low [0.12 +/- 0.04 mol P/mol of the 20,000-Da light chain (LC 20)]. Phosphorylation was slightly (but not significantly) higher in the presence of 10 microM histamine in the relaxed state between contractions (0.20 +/- 0.03 mol P/mol LC 20). In muscle strips frozen during force development, when force had reached half of its peak value, phosphorylation was 0.38 +/- 0.06 mol P/mol LC 20. The highest levels of phosphorylation (0.49 +/- 0.04 mol P/mol LC 20) were found in strips frozen at the peak of the rhythmic contractions. Strips frozen when force had declined to half of the peak force showed low levels of phosphorylation (0.17 +/- 0.07 mol P/mol LC 20), indicating that the myosin light chain phosphatase activity was quite high. Mathematical modeling of the kinase and phosphatase reactions suggested that the apparent first-order phosphatase rate constant was at least 0.08 s-1 under these conditions. To obtain a better estimate of this rate constant, a second series of phosphorylation measurements were made early in the relaxation phase of the rhythmic contractions. The highest phosphatase rate constant obtained from these measurements was 0.23 s-1.(ABSTRACT TRUNCATED AT 250 WORDS)


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Signal Transduction in Smooth Muscle: Invited Review: Regulation of myosin phosphorylation in smooth muscle
J Appl Physiol, July 1, 2001; 91(1): 497 - 503.
[Abstract] [Full Text] [PDF]


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