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Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104
We studied
effects of increasing the length of porcine trachealis muscle on 5.5 µM carbachol (CCh)-evoked phosphatidylinositol 4,5-bisphosphate
[PI(4,5)P2] synthesis and other parameters
of phosphatidylinositol (PI) turnover.
PI(4,5)P2 resynthesis rates in muscle held at
1.0 optimal length (Lo), measured over the first 6 min of CCh stimulation, were 140 ± 12 and 227 ± 14% of
values found in muscle held at 0.5 Lo and in
free-floating muscle, respectively. Time-dependent changes in cellular
masses of PI(4,5)P2, PI, and phosphatidic
acid, and PI resynthesis rates, were also altered by the muscle length
at which contraction occurred. In free-floating muscle, CCh did not
evoke increases in tyrosine-phosphorylated paxillin (PTyr-paxillin), an
index of
1-integrin signaling; however, there were
progressive increases in PTyr-paxillin in muscle held at 0.5 and 1.0 Lo during contraction, which correlated with
increases in PI(4,5)P2 synthesis rates. These
data indicate that PI(4,5)P2 synthesis rates
and other parameters of CCh-stimulated inositol phospholipid turnover
are muscle length-dependent and provide evidence that supports the
hypothesis that length-dependent
1-integrin signals may
exert control on CCh-activated PI(4,5)P2 synthesis.
smooth muscle mechanical strain; airway smooth muscle; phosphatidylinositol 4,5-bisphosphate; integrins; phosphatidylinositol 4-kinase; phosphatidylinositol 4,5-bisphosphate
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