Phosphorylation of calponin in airway smooth muscle.
Pohl, Jennifer, Steven J. Winder, Bruce G. Allen, Michael P. Walsh,
James R. Sellers, and William T. Gerthoffer.
Department of Pharmacology, University of Nevada School of
Medicine, Reno, NV 89557 and Smooth Muscle Research Group, Faculty of
Medicine, University of Calgary, Calgary, Alberta, Canada T2N 4N1
APStracts 3:0161L, 1996.
Calponin is an actin-binding protein known to be a substrate in vitro
for several protein kinases and phosphoprotein phosphatases. We
tested the hypothesis that calponin is phosphorylated in vivo using
canine tracheal smooth muscle strips metabolically labeled with 32Pi.
Calponin was gel purified from muscles stimulated with 1 (M
carbachol. Phosphorylation increased to 2.0-times the basal level of
178 (( 26) cpm/(g calponin within 30 sec to 350 (( 64) cpm/(g. Two
-dimensional non-equilibrium pH-gradient gel electrophoresis resolved
four charge isoforms of calponin in unstimulated muscle. Stimulation
with carbachol induced an additional more acidic isoform.
Phosphorylation of calponin in vitro with PKC also induced formation
of additional acidic isoforms. The functional effect of
phosphorylation was demonstrated using an in vitro motility assay in
which unphosphorylated calponin (2 (M) caused a profound inhibition
of actin sliding. Calponin phosphorylated by PKC did not inhibit
actin sliding. The results show phosphorylation of calponin occurs in
intact tracheal smooth muscle, and that phosphorylation of calponin
in vitro alleviates the inhibitory effect of calponin on actomyosin
function.
Received 16 January 1996; accepted in final form 30 August 1996.
APS Manuscript Number L15-6.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996