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Published online before print June 14, 2006
Eur Respir J 2006, doi:10.1183/09031936.06.00025506
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ORIGINAL ARTICLE

Regulation of airway smooth muscle RhoA/ROCK activities by cholinergic and bronchodilator stimuli

C. Liu 1, J. Zuo 1, L.J. Janssen 1*

1 Firestone Institute for Respiratory Health, St. Joseph's Hospital and the Dept of Medicine, McMaster University, Hamilton, Ontario L8N 3Z5, Canada

* To whom correspondence should be addressed. E-mail: janssenl{at}mcmaster.ca.


  Abstract

We compared the temporal relationships of Rho activity, ROCK activity and tone following cholinergic stimulation in the presence and absence of three different bronchodilators. Bovine trachea challenged with a half-maximally effective concentration of CCh was flash-frozen at different times, then assayed for Rho (rhotekin pull-down assay) and ROCK activities (Western blot; radiometric assay). Rho was activated within 30s, followed by ROCK (peak at 2 min); both returned to baseline by 20 min, although tone continued to rise over that period. Increasing the concentration of CCh greatly increased the magnitudes and rates of stimulation of Rho, ROCK and tone. These CCh-induced changes were next compared in tissues pretreated with isoproterenol (ISO), salmeterol (SAL) or the nitric oxide donor SNAP. Neither time-course nor magnitude of Rho-activation were reduced by the {beta}-agonists; SNAP, however, slowed Rho activation but did not alter the peak magnitude. These observations were mirrored in ROCK-activation and contraction. In tissues first preconstricted with CCh and then challenged with the bronchodilators, however, all three agonists reversed cholinergically-stimulated Rho, ROCK and myosin light chain kinase activities as well as tone. We conclude that bronchodilators can suppress RhoA and ROCK activities, although their major effect appears to be on MLCK activity.

Keywords:  Adrenergic, airway smooth muscle, cholinergic, contraction, myosin, nitric oxide, relaxation, RhoA, ROCK




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