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Articles in PresS, published online ahead of print October 18, 2002
Am J Physiol Lung Cell Mol Physiol, 10.1152/ajplung.00159.2002
Submitted on May 22, 2002
Accepted on October 2, 2002
1 Departments of Anesthesiology and Physiology and Biophysics, Mayo Clinic, Rochester, MN, USA
2 Department of Biochemistry, University of Nevada, Reno, Reno, NV, USA
* To whom correspondence should be addressed. E-mail: perkinsw{at}mayo.edu.
The purpose of this study was to test the hypothesis that hydrogen peroxide (H2O2) decreases the amount of force produced by a given intracellular [Ca2+] (i.e., the calcium sensitivity) in airway smooth muscle (ASM) in part by mechanisms independent of changes in regulatory myosin light chain (rMLC) phosphorylation. A new preparation was developed and validated in which canine ASM strips were first exposed to H2O2, then permeabilized with 10% Triton X-100 to assess the persistent effects of H2O2 on calcium sensitivity. Experiments in which H2O2 was administered before permeabilization revealed a novel mechanism which contributed to reduced calcium sensitivity independent of changes in rMLC phosphorylation , in addition to a rMLC phosphorylation-dependent mechanism. The mechanism depended on factors not available in the permeabilized ASM strip or in the buffer to which the strip was exposed, as there was no effect when H2O2 was added to permeabilized strips. H2O2 treatment of a maximally thiophosphorylated purified myosin subfragment (HMM) significantly reduced actomyosin ATPase activity, suggesting one mechanism by which the phosphorylation-independent reduction in calcium sensitivity may occur.
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