Effects of calponin on force generation by single smooth muscle
cells.
Horowitz, Arie, Odille Cl[acute]ement-Chomienne, Michael P. Walsh,
Terence Tao, Hideaki Katsuyama, and Kathleen G. Morgan.
Cardiovascular Division, Beth Israel Hospital, and Program in
Smooth Muscle Research, Department of Medicine, Harvard Medical
School, Boston, MA 02215; Boston Biomedical Research Institute,
Boston, MA 02114; Department of Biochemistry, Tufts University School
of Medicine; Smooth Muscle Research Group and Department of Medical
Biochemistry, University of Calgary, Calgary, Alberta T2N 4N1,
Canada
APStracts 3:0093H, 1996.
Although the actin-binding and actomyosin ATPase inhibitory properties
of calponin are well documented in vitro, its function in the smooth
muscle cell has not been elucidated. To address this question, we
utilized the ferret aortic smooth muscle cell, which shows a protein
kinase C-dependent contraction even at pCa (-log [Ca2+]) 9.0 in the
absence of a change in myosin light chain phosphorylation. Force was
recorded from single, briefly permeabilized cells stimulated via a
Ca2+-independent pathway by either phenylephrine or the isoenzyme of
protein kinase C. Treatment of stimulated cells with wild-type
recombinant calponin reduced steady-state contractile force by 45
-60%. When calponin application preceded protein kinase C treatment,
contraction was completely suppressed. On the other hand, calponin
phosphorylated at Ser175 or mutant calponin with a Ser175 >Ala
replacement had no effect on contractile force. A peptide
corresponding to Leu166 Gly194 of calponin, which included an actin
-binding domain but excluded the actomyosin ATPase inhibitory region,
was synthesized. Treatment of aortic smooth muscle cells with this
peptide triggered a concentration-dependent contraction, presumably
by alleviating the inhibitory effect of endogenous calponin. A
control peptide with a scrambled sequence of the same residues
produced no detectable contractile response. Although other
interpretations are possible, these results are consistent with the
view that calponin participates in thin filament-mediated regulation
of smooth muscle contraction, and that it may be part of a Ca2+
-independent pathway downstream of protein kinase C .
Received 14 November 1995; accepted in final form 23 January
1996.
APS Manuscript Number H1070-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 March 96