AJP - Cell Physiology, Vol 259, Issue 2 C315-C324, Copyright © 1990 by American Physiological Society
Peptide modulators of myosin light chain kinase affect smooth muscle cell contraction
G. J. Kargacin, M. Ikebe and F. S. Fay
Department of Physiology, University of Massachusetts Medical School, Worcester 01655.
To examine the importance of myosin light chain kinase (MLCK) in the
initiation of contraction in smooth muscle, we used a constitutively active
form of MLCK (IMLCK) and two specific peptide inhibitors of MLCK to study
the activation of skinned single smooth muscle cells. Although unregulated
by Ca-calmodulin, IMLCK, in vitro, was found to have biochemical properties
like those of MLCK. Upon photolysis of caged ATP, IMLCK caused Ca-free
shortening of skinned cells similar in time course and extent to that
induced by Ca2+. Two peptide probes, RS-20 and SM-1, patterned after the
Ca-calmodulin binding site and a pseudosubstrate inhibitory site,
respectively, of the native MLCK molecule, were shown to specifically
inhibit MLCK in in vitro experiments. Both peptides dose dependently
inhibited Ca-induced shortening of skinned single cells. These results
indicate that MLCK plays an essential role in the activation process in the
smooth muscle cell in that activation of this enzyme is both necessary and
sufficient for the initiation of contraction.
