Smooth muscle length-dependent PI(4,5)P2 synthesis and paxillin tyrosine phosphorylation

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)P 2 ] synthesis and other parameters of phosphatidylinositol (PI) turnover. PI(4,5)P 2 resynthesis rates in muscle held at 1.0 optimal length ( L o ), measured over the first 6 min of CCh stimulation, were 140 ± 12 and 227 ± 14% of values found in muscle held at 0.5 L o and in free-floating muscle, respectively. Time-dependent changes in cellular masses of PI(4,5)P 2 , 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 L o during contraction, which correlated with increases in PI(4,5)P 2 synthesis rates. These data indicate that PI(4,5)P 2 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)P 2 synthesis. smooth muscle mechanical strain; airway smooth muscle; phosphatidylinositol 4,5-bisphosphate; integrins; phosphatidylinositol 4-kinase; phosphatidylinositol 4,5-bisphosphate