title: Hyperoxic conditions inhibit airway smooth muscle myosin phosphatase in rat pups.
abstract: Exposure of rat pups to 100% oxygen is a model for studying neonatal lung injury. Airway reactivity is increased in this model, in part due to impaired airway smooth muscle (ASM) relaxation. We compared biochemical determinants of ASM contractility in rat pups exposed to 100% oxygen for 7 days vs. littermates raised in room air. The baseline quantities of ASM contractile proteins, extent of phosphorylation of the 20-kDa myosin regulatory light chain (LC(20)), and amount of the myosin-binding subunit of smooth muscle myosin phosphatase (MYPT) were all comparable between the two groups. Bethanechol-induced contraction increased the extent of phosphorylation of both LC(20) and MYPT in the hyperoxic group (45% and 70% over control, respectively). Relaxation after electrical field stimulation demonstrated greater phosphorylation of both LC(20) and MYPT in the hyperoxic group compared with controls (67% and 84%, respectively). To determine if hyperoxia induced changes in the isoforms of MYPT, isoform expression was also compared but differences were not found. To determine potential mechanisms whereby MYPT phosphorylation was increased by hyperoxia, separate tracheas were treated with the Rho kinase inhibitor Y-27632. This treatment completely eliminated differences in MYPT phosphorylation between the groups. Because phosphorylation of MYPT impairs the phosphatase activity of myosin phosphatase, these data suggest that hyperoxic conditioning during early postnatal life impairs relaxation through prolonging LC(20) phosphorylation. This mechanism might contribute to increased ASM reactivity seen in bronchopulmonary dysplasia.
authors.affiliation: Department of Pediatrics, Case Western Reserve University, 11100 Euclid Ave., Cleveland, OH 44106, USA. pgs3@case.edu
authors.forename: Paul G
authors.initials: PG
authors.lastname: Smith
authors.forename: Albana
authors.initials: A
authors.lastname: Dreshaj
authors.forename: Subhendu
authors.initials: S
authors.lastname: Chaudhuri
authors.forename: Baran M
authors.initials: BM
authors.lastname: Onder
authors.forename: Maroun J
authors.initials: MJ
authors.lastname: Mhanna
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Martin
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D016535:Bronchial Hyperreactivity / Q000201:enzymology / Q000209:etiology; D004195:Disease Models, Animal; D006801:Humans; D018496:Hyperoxia / Q000201:enzymology*; D007231:Infant, Newborn; D009130:Muscle, Smooth / Q000201:enzymology*; D018994:Myosin Light Chains / Q000378:metabolism; D043263:Myosin-Light-Chain Phosphatase / Q000037:antagonists & inhibitors*; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley; D014132:Trachea / Q000201:enzymology*
chemical_list: D018994:Myosin Light Chains; D043263:Myosin-Light-Chain Phosphatase