Increased myosin light chain kinase (mlck) content in saphenous
vein from a canine model of anaphylactic shock.
Liu, Gang, Xueliang Liu, Kang Rao, He Jiang, and Newman L. Stephens.
Department of Physiology, Faculty of Medicine, University of
Manitoba
APStracts 2:0406A, 1995.
Our previous mechanical studies revealed that smooth muscle from
sensitized canine saphenous vein demonstrated greater active
shortening capacity, and maximum shortening velocity vis-[grave]a-vis
the control. Relaxation of the muscle was also prolonged. These
functional changes could be responsible for the hyperreactivity of
venous smooth muscle observed in anaphylactic shock. Because smooth
muscle cross-bridge cycling is a function of actomyosin ATPase
activity which is itself regulated by MLCK dependent phosphorylation
of the 20 kDa myosin light chain (MLC20), we assessed the
stoichiometry of MLC20 phosphorylation and the content and activity
of MLCK in homogenates of saphenous vein smooth muscle obtained from
ragweed pollen-sensitized dogs and littermate controls. We found that
phosphorylation of MLC20 in sensitized saphenous vein (SSV)
homogenate as measured by urea-polyacrylamide gel electrophoresis was
significantly higher (42.26 +/-5.1%) compared to controls (26.69 +/-
3.3% p<0.05); MLCK content as measured by SDS-PAGE and
quantified by densitometry was also significantly (P<0.05)
higher in SSV homogenates (0.169 [mu]g/mg protein +/- 0.019 SE) than
in controls (0.075 [mu]g/mg protein +/-0.004 SE). Total myosin light
chain kinase activity increased significantly (P<0.05) from 6.16
Pi x 10-5 nmol/mg fresh weight of tissue /min. +/- 0.6 SE in control
homogenates, to 12.5 Pi x 10-5 nmol/mg fresh weight of tissue
/min.,+/- 2.5 SE in sensitized. Specific MLCK activity was, however,
similar in sensitized and control homogenates. The higher level of
MLC20 phosphorylation was associated with increased MLCK content. The
results of our study suggest that elevation of MLCK content in the
homogenate could account for the increased mechanical reactivity of
the sensitized venous smooth muscle in anaphylactic shock. These
studies are supported by the fact that similar findings have been
reported by us for rapidly frozen intact strips of airway smooth
muscle.
Received 27 December 1994; accepted in final form 8 September
1995.
APS Manuscript Number A1337-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 31 October 95