Force augmentation and stimulated actin polymerization in swine carotid artery

Abstract

Tejani AD, Rembold CM. Force augmentation and stimulated actin polymerization in swine carotid artery. Am J Physiol Cell Physiol 298: C182-C190, 2010. First published October 14, 2009 doi:10.1152/ajpcell.00326.2009.-The phenomenon of posttetanic potentiation, in which a single submaximal contraction or series of submaximal contractions strengthens a subsequent contraction, has been observed in both skeletal and cardiac muscle. In this study, we describe a similar phenomenon in swine carotid arterial smooth muscle. We find that a submaximal K ϩ depolarization increases the force generation of a subsequent maximal K ϩ depolarization; we term this "force augmentation." Force augmentation was not associated with a significant increase in crossbridge phosphorylation or shortening velocity during the maximal K ϩ depolarization, suggesting that the augmented force was not caused by higher crossbridge phosphorylation or crossbridge cycling rates. We found that the characteristics of the tissue before the maximal K ϩ depolarization predicted the degree of force augmentation. Specifically, measures of stimulated actin polymerization (higher prior Y118 paxillin phosphorylation, higher prior F-actin, and transition to a more solid rheology evidenced by lower noise temperature, hysteresivity, and phase angle) predicted the subsequent force augmentation. Increased prior contraction alone did not induce force augmentation since readdition of Ca 2ϩ to Ca 2ϩ -depleted tissues induced a partial contraction that was not associated with changes in noise temperature or with subsequent force augmentation. These data suggest that stimulated actin polymerization may produce a substrate for increased crossbridge mediated force, a process we observe as force augmentation. phase angle; noise temperature; paxillin; rheology; vascular smooth muscle IN SKELETAL AND CARDIAC MUSCLE, a single submaximal contraction resulting from a single action potential is referred to as a twitch, and the sustained contraction resulting from repetitive action potentials is referred to as tetanus. In both skeletal and cardiac muscle, both twitches and submaximal tetany will potentiate a subsequent contraction induced by maximal tetany, a phenomenon termed posttetanic potentiation. Skeletal muscle posttetanic potentiation is thought to be caused by crossbridge phosphorylation (31). In this study, we describe a similar phenomenon in arterial smooth muscle in which a submaximal K ϩ contraction increases the maximum force of a subsequent maximal K ϩ contraction, a phenomenon we term "force augmentation." We find, however, that force augmentation in smooth muscle is associated with stimulated actin polymerization and not by increased crossbridge phosphorylation or shortening velocity.It is widely accepted that most forms of arterial smooth muscle contraction primarily involve increased myoplasmic calcium ([Ca 2ϩ ] i ), which increases crossbridge phosphorylation on Ser 19 of the myosin regulatory light chain (MRLC) via MRLC kinase (reviewed in Ref. 15). Contr...

Tissue length modulates “stimulated actin polymerization,” force augmentation, and the rate of swine carotid arterial contraction

“…We previously showed that prior partial activation of arterial smooth muscle increased the magnitude of the initial force response to a maximal K ϩ -depolarizing stimulus by ϳ15%, a process that we termed force augmentation (29). We also previously reported that force augmentation correlated with prior stimulated actin polymerization, as measured by increases in Y118 paxillin phosphorylation, F-actin content, and a change to a more solid rheology, as measured by a decline in noise temperature.…”

“…We found that force augmentation was associated with prior increases in measures of stimulated actin polymerization, but not with increases in cross-bridge phosphorylation or shortening velocity, suggesting that stimulated actin polymerization determines force augmentation (29).…”

“…As we previously reported, Y118 paxillin phosphorylation was significantly increased by 2 min after the first maximal contraction and remained significantly elevated throughout the augmentation protocol. Since Y118 paxillin phosphorylation was significantly higher prior to the second (augmented) contraction (30 min) than prior to the first (nonaugmented) contraction (0 min), we proposed a potential role for Y118 paxillin phosphorylation in force augmentation (29). The first and second maximal 109 mM K ϩ contractions caused significant decreases in S3 cofilin phosphorylation.…”

“…In Fig. 1, we evaluated whether prior S3 cofilin phosphorylation was associated with force augmentation at 1.0 L o by analyzing the tissue homogenates that we previously studied for Y118 paxillin phosphorylation (29). Swine arterial smooth muscle was maximally depolarized with 109 mM K ϩ for 2 min, partially activated with 25 mM K ϩ for 28 min (with 3 changes of the solution to ensure full washout of the 109 mM K ϩ ), and finally maximally depolarized a second time with 109 mM K ϩ for 30 min.…”

The effect of low dose lipopolysaccharide on thyroid hormone-regulated actin cytoskeleton modulation and type 2 iodothyronine deiodinase activity in astrocytes

“…Relative amount of F-actin vs. G-actin in cells was determined as previously reported [34]. In brief, lysis buffer contains 50 mM piperazine-N, N'-bis (2-ethanesulfonic acid), 50 mM NaCl, 5 mM MgCl 2 , 5 mM EGTA, 5% glycerol, 0.1% Nonidet P-40, 0.1% Triton X-100, 0.1% Tween 20, and 0.1% β-mercapto-ethanol, pH 6.9, at room temperature.…”