Journal
AMERICAN JOURNAL OF PHYSIOLOGY-CELL PHYSIOLOGY
Volume 289, Issue 1, Pages C12-C21Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/ajpcell.00418.2004
Keywords
muscle mechanics; preconditioning; Y-27632; RhoA kinase; passive force
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Funding
- NIDDK NIH HHS [R01-DK59620] Funding Source: Medline
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Passive mechanical properties of strips of rabbit detrusor smooth muscle were examined and found by cyclic loading in a calcium-free solution to display viscoelastic softening and strain-induced stress softening ( strain softening). Strain softening, or the Mullins effect, is a loss of stiffness attributed to the breakage of cross-links, and appeared irreversible in detrusor even after the return of spontaneous rhythmic tone during 120 min of incubation in a calcium-containing solution. However, 3 min of KCl or carbachol (CCh)-induced contraction permitted rapid regeneration of the passive stiffness lost to strain softening, and 3 mu M of the RhoA kinase (ROK) inhibitor Y-27632 prevented this regeneration. The degree of ROK-induced passive stiffness was inversely dependent on muscle length over a length range where peak CCh-induced force was length independent. Thus rabbit detrusor displayed variable passive stiffness both strain- and activation-history dependent. In conclusion, activation of ROK by KCl or CCh increased passive stiffness softened by muscle strain and thereby attributed to cross-links that remained stable during tissue incubation in a calcium-free solution. Degradation of this signaling system could potentially contribute to urinary incontinence.
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