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F‐actin stabilization increases tension cost during contraction of permeabilized airway smooth muscle in dogs
Author(s) -
Jones Keith A.,
Perkins William J.,
Lorenz Robert R.,
Prakash Y. S.,
Sieck Gary C.,
Warner David O.
Publication year - 1999
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1999.0527m.x
Subject(s) - isometric exercise , biophysics , actin , muscle contraction , myosin , chemistry , contractility , contraction (grammar) , atp hydrolysis , adenosine triphosphate , oxidative phosphorylation , myosin light chain kinase , biochemistry , biology , anatomy , medicine , atpase , endocrinology , enzyme
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 Ca 2+ ‐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 ( V max ) was estimated by interpolation of the force‐velocity relationship to zero load during isotonic loading. 4 Maximal activation with 10 μ m free Ca 2+ 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 μ m 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 V max 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.