J. C. Dallon 1 and H. Paul Ehrlich 2
1: Department of Mathematics, Brigham Young University,
Provo, UT 84602-6539
2: Division of Plastic Surgery, Department of Surgery, Milton S. Hershey Medical Center, Hershey, PA
Both rat derived vascular smooth muscle cells (SMC) and human
myofibroblasts contain $\alpha$ smooth muscle actin (SMA), but they utilize
different mechanisms to contract populated collagen lattices (PCLs).
The difference is in how the cells generate the force that contracts
the lattices. Human dermal fibroblasts transform into
myofibroblasts, expressing $\alpha$-SMA within stress fibers, when cultured
in lattices that remain attached to the surface of a tissue culture
dish. When attached lattices are populated with rat derived
vascular SMC, the cells retain their vascular SMC phenotype.
Comparing the contraction of attached PCLs when they are released
from the culture dish on day 4 shows that lattices populated with
rat vascular SMC contract less than those populated with human
myofibroblast. PCL contraction was evaluated in the presence of
vanadate and genistein, which modify protein tyrosine
phosphorylation, and ML-7 and Y-27632, which modify myosin ATPase
activity. Genistein and ML-7 had no affect upon either
myofibroblast or vascular SMC-PCL contraction, demonstrating that
neither protein tyrosine kinase nor myosin light chain kinase was
involved. Vanadate inhibited myofibroblast-PCL contraction,
consistent with a role for protein tyrosine phosphatase activity
with myofibroblast-generated forces. Y-27632 inhibited both SMC and
myofibroblast PCL contraction, consistent with a central role of
myosin light chain phosphatase.
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