AJP - Cell Physiology, Vol 262, Issue 6 C1446-C1455, Copyright © 1992 by American Physiological Society
Polylysine activates smooth muscle actin-myosin interaction without LC20 phosphorylation
P. T. Szymanski, J. D. Strauss, G. Doerman, J. DiSalvo and R. J. Paul
Department of Physiology and Biophysics, College of Medicine, University of Cincinnati, Ohio 45267-0576.
Phosphorylation/dephosphorylation of the 20-kDa light chain of smooth
muscle myosin is a major regulator of actin-myosin interaction. Phosphatase
inhibitors have thus been shown to enhance contraction in smooth muscle.
The activity of type II phosphatase against phosphorylated myosin light
chains is inhibited by polylysine. Thus we studied the effects of
polylysine (10-13 kDa) on actin-myosin interaction in permeabilized guinea
pig taenia coli fibers and in bovine aortic actomyosin. Addition of
polylysine (10-20 microM) to Ca-ethylene glycol-bis(beta-aminoethyl
ether)-N,N,N',N'-tetraacetic acid buffered solution ([Ca2+] less than 0.01
microM) elicited a contraction in fibers of 40 +/- 8% (n = 6) of maximally
stimulated contractions ([Ca2+] congruent to 1.5 microM). Untreated fibers
did not generate any significant force in parallel control experiments.
Similarly, polylysine stimulated the ATPase activity both in fibers and
actomyosin in a dose-dependent manner. This stimulation could be completely
inhibited and abolished upon addition of heparin, a negatively charged
heteropolysaccharide. In actomyosin previously phosphorylated with ATP
gamma S, polylysine in a concentration range of 2-13 microM did not further
stimulate enzyme activity. These increases in activity were not connected
with significant changes in the phosphorylation of 20-kDa myosin light
chain nor could any incorporation of 32P associated with polylysine
stimulation be detected in both skinned fibers and actomyosin by
autoradiography of SDS gels. Our data indicate that polylysine increases
actin-myosin interaction in both smooth muscle model systems by directly
influencing contractile proteins. As such, polylysine may be a useful probe
for the mechanism of activation of smooth muscle.
