title: Evidence that actomyosin cross bridges contribute to "passive" tension in detrusor smooth muscle.
abstract: Contraction of detrusor smooth muscle (DSM) at short muscle lengths generates a stiffness component we termed adjustable passive stiffness (APS) that is retained in tissues incubated in a Ca(2+)-free solution, shifts the DSM length-passive tension curve up and to the left, and is softened by muscle strain and release (strain softened). In the present study, we tested the hypothesis that APS is due to slowly cycling actomyosin cross bridges. APS and active tension produced by the stimulus, KCl, displayed similar length dependencies with identical optimum length values. The myosin II inhibitor blebbistatin relaxed active tension maintained during a KCl-induced contraction and the passive tension maintained during stress-relaxation induced by muscle stretch in a Ca(2+)-free solution. Passive tension was attributed to tension maintaining rather than tension developing cross bridges because tension did not recover after a rapid 10% stretch and release as it did during a KCl-induced contraction. APS generated by a KCl-induced contraction in intact tissues was preserved in tissues permeabilized with Triton X-100. Blebbistatin and the actin polymerization inhibitor latrunculin-B reduced the degree of APS generated by a KCl-induced contraction. The degree of APS generated by KCl was inhibited to a greater degree than was the peak KCl-induced tension by rhoA kinase and cyclooxygenase inhibitors. These data support the hypothesis that APS is due to slowly cycling actomyosin cross bridges and suggest that cross bridges may play a novel role in DSM that uniquely serves to ensure proper contractile function over an extreme working length range.
authors.affiliation: Departments of Biochemistry and Molecular Biology, Virginia Commonwealth University School of Medicine, Richmond, Virginia 23298-0614, USA. phratz@vcu.edu
authors.forename: Paul H
authors.initials: PH
authors.lastname: Ratz
authors.forename: John E
authors.initials: JE
authors.lastname: Speich
mesh_terms: D000205:Actomyosin / Q000378:metabolism*; D000818:Animals; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D003902:Detergents / Q000737:chemistry; D056966:Excitation Contraction Coupling / Q000187:drug effects; D005260:Female; D006576:Heterocyclic Compounds, 4 or More Rings / Q000494:pharmacology; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D024462:Myosin Type II / Q000037:antagonists & inhibitors / Q000378:metabolism; D009218:Myosins / Q000378:metabolism; D017830:Octoxynol / Q000737:chemistry; D011189:Potassium Chloride / Q000494:pharmacology; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011817:Rabbits; D053778:Thiazolidines / Q000494:pharmacology; D013997:Time Factors; D001743:Urinary Bladder / Q000187:drug effects / Q000378:metabolism*; D054460:rho-Associated Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D019086:Bridged Bicyclo Compounds, Heterocyclic; D016861:Cyclooxygenase Inhibitors; D003902:Detergents; D006576:Heterocyclic Compounds, 4 or More Rings; D047428:Protein Kinase Inhibitors; D053778:Thiazolidines; C472645:blebbistatin; D011189:Potassium Chloride; D017830:Octoxynol; D000205:Actomyosin; D011451:Prostaglandin-Endoperoxide Synthases; D054460:rho-Associated Kinases; D024462:Myosin Type II; D009218:Myosins; C037068:latrunculin B; D002118:Calcium