AJP - Cell Physiology, Vol 259, Issue 2 C258-C265, Copyright © 1990 by American Physiological Society
Substance P contracts bovine tracheal smooth muscle via activation of myosin light chain kinase
M. A. Corson, J. R. Sellers, R. S. Adelstein and M. Schoenberg
Laboratory of Molecular Cardiology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892.
At near-threshold substance P concentrations, the isometric tension
response of bovine tracheal strips is almost completely abolished by
atropine, indicating mediation of contraction via substance P-stimulated
release of acetylcholine from prejunctional nerve terminals. At
near-maximal concentrations, the atropine-inhibited component of the
tension response is less than 25%, indicating mainly direct activation.
Under conditions in which activation by substance P is direct, peak tension
is reached in approximately 11 min. Immunoblot analysis of the time course
of phosphorylation of the 20-kDa myosin light chain (LC20) reveals
incorporation of approximately 0.5 mol phosphate/mol light chain at 10 min.
Two-dimensional tryptic phosphopeptide analysis of phosphorylated light
chain reveals a single major phosphopeptide. The peptide migrates
identically with that produced by myosin light chain kinase phosphorylation
of purified tracheal myosin in vitro. Contraction stimulated by
acetylcholine is more rapid, with attainment of peak tension in 2.5 min and
a peak LC20 phosphorylation of 0.65 mol/mol. These results indicate that 1)
substance P mediates contraction of bovine trachea both directly and
indirectly, and 2) under conditions in which activation is direct, the
tension and phosphorylation responses qualitatively resemble those observed
with acetylcholine.
