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Updated: Jul 17, 2026
Isolation of Pulmonary Artery Smooth Muscle Cells from Neonatal Mice
Published on: October 19, 2013
Hyperoxic conditions inhibit airway smooth muscle myosin phosphatase in rat pups
Paul G Smith1, Albana Dreshaj, Subhendu Chaudhuri
1Department of Pediatrics, Case Western Reserve University, 11100 Euclid Ave., Cleveland, OH 44106, USA. pgs3@case.edu
Insights
Neonatal exposure to high oxygen impairs airway smooth muscle relaxation by prolonging myosin light chain phosphorylation. This mechanism may contribute to increased airway reactivity in conditions like bronchopulmonary dysplasia.
Area of Science:
- Neonatal physiology
- Pulmonary medicine
- Smooth muscle biology
Background:
- Neonatal lung injury models are crucial for understanding respiratory diseases.
- Hyperoxia exposure in rat pups increases airway reactivity.
- Impaired airway smooth muscle (ASM) relaxation contributes to this increased reactivity.
Purpose of the Study:
- To compare biochemical factors influencing ASM contractility in rat pups exposed to hyperoxia versus room air.
- To investigate the role of myosin light chain phosphorylation in hyperoxia-induced ASM dysfunction.
Main Methods:
- Rat pups were exposed to 100% oxygen for 7 days.
- ASM contractile proteins, myosin light chain (LC(20)) phosphorylation, and myosin phosphatase (MYPT) binding subunit levels were quantified.
- Electrical field stimulation and bethanechol were used to induce contraction and assess relaxation.
- Rho kinase inhibitor (Y-27632) was used to explore mechanisms of MYPT phosphorylation.
Main Results:
- Baseline ASM contractile protein levels and LC(20)/MYPT phosphorylation were similar between groups.
- Hyperoxia increased LC(20) and MYPT phosphorylation during both contraction and relaxation phases.
- Hyperoxia did not alter MYPT isoform expression.
- Y-27632 treatment abolished hyperoxia-induced differences in MYPT phosphorylation.
Conclusions:
- Hyperoxic conditioning in early life impairs ASM relaxation by prolonging LC(20) phosphorylation.
- Increased MYPT phosphorylation, mediated by Rho kinase, is a key mechanism.
- This impaired relaxation may contribute to the increased airway reactivity observed in bronchopulmonary dysplasia.
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.