title: F-actin stabilization increases tension cost during contraction of permeabilized airway smooth muscle in dogs.
abstract: 1. Dynamic actin reorganization involving actin polymerization and depolymerization may play an important functional role in smooth muscle. 2. This study tested the hypothesis that F-actin stabilization by phalloidin increases tension cost (i.e. ATP hydrolysis rate per unit of isometric force) during Ca2+-induced activation of Triton X-100-permeabilized canine tracheal smooth muscle. 3. Adenosine 5'-triphosphate (ATP) hydrolysis rate was quantified using an enzyme-coupled NADH fluorometric technique, regulatory myosin light chain (rMLC) phosphorylation was measured by Western blot analysis, and maximum unloaded shortening velocity (Vmax) was estimated by interpolation of the force-velocity relationship to zero load during isotonic loading. 4. Maximal activation with 10 microM free Ca2+ induced sustained increases in isometric force, stiffness, and rMLC phosphorylation. However, the increase in ATP hydrolysis rate initially reached peak values, but then declined to steady-state levels above that of the unstimulated muscle. Thus, tension cost decreased throughout steady-state isometric force. 5. Following incubation of permeabilized strips with 50 microM phalloidin for 1 h, the increases in isometric force and stiffness were not sustained despite a sustained increase in rMLC phosphorylation. Also, after an initial decline, tension cost increased throughout activation. Phalloidin had no effect on Vmax during steady-state isometric force or on rMLC phosphorylation. 6. These findings suggest that dynamic reorganization of actin is necessary for optimal energy utilization during contraction of permeabilized airway smooth muscle.
authors.affiliation: Departments of Anesthesiology, and Physiology and Biophysics, Mayo Clinic and Mayo Foundation, Rochester, MN 55905, USA. kjones@mayo.edu
authors.forename: K A
authors.initials: KA
authors.lastname: Jones
authors.forename: W J
authors.initials: WJ
authors.lastname: Perkins
authors.forename: R R
authors.initials: RR
authors.lastname: Lorenz
authors.forename: Y S
authors.initials: YS
authors.lastname: Prakash
authors.forename: G C
authors.initials: GC
authors.lastname: Sieck
authors.forename: D O
authors.initials: DO
authors.lastname: Warner
mesh_terms: D000199:Actins / Q000378:metabolism / Q000502:physiology*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000502:physiology; D004285:Dogs; D004558:Electric Stimulation; D004734:Energy Metabolism / Q000187:drug effects / Q000502:physiology; D005260:Female; D006868:Hydrolysis; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000187:drug effects / Q000502:physiology; D008297:Male; D008856:Microscopy, Fluorescence; D009119:Muscle Contraction / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D018994:Myosin Light Chains / Q000378:metabolism; D017830:Octoxynol / Q000494:pharmacology; D010590:Phalloidine / Q000494:pharmacology; D010766:Phosphorylation; D014132:Trachea / Q000187:drug effects / Q000502:physiology
chemical_list: D000199:Actins; D018994:Myosin Light Chains; D010590:Phalloidine; D000255:Adenosine Triphosphate; D017830:Octoxynol; D002118:Calcium