scholarly journals Regulatory light chain phosphorylation augments length-dependent contraction in PTU-treated rats

2018 ◽  
Vol 151 (1) ◽  
pp. 66-76 ◽  
Author(s):  
Jason J. Breithaupt ◽  
Hannah C. Pulcastro ◽  
Peter O. Awinda ◽  
David C. DeWitt ◽  
Bertrand C.W. Tanner
Keyword(s):  
Myosin Heavy Chain ◽  
Heavy Chain ◽  
Light Chain ◽  
Myosin Heavy Chain Isoforms ◽  
Regulatory Light Chain ◽  
Cardiac Myosin ◽  
Myosin Heavy Chain Isoform ◽  
Cross Bridge ◽  
Detachment Rate ◽  
Length Dependent Activation

Force production by actin–myosin cross-bridges in cardiac muscle is regulated by thin-filament proteins and sarcomere length (SL) throughout the heartbeat. Prior work has shown that myosin regulatory light chain (RLC), which binds to the neck of myosin heavy chain, increases cardiac contractility when phosphorylated. We recently showed that cross-bridge kinetics slow with increasing SLs, and that RLC phosphorylation amplifies this effect, using skinned rat myocardial strips predominantly composed of the faster α-cardiac myosin heavy chain isoform. In the present study, to assess how RLC phosphorylation influences length-dependent myosin function as myosin motor speed varies, we used a propylthiouracil (PTU) diet to induce >95% expression of the slower β-myosin heavy chain isoform in rat cardiac ventricles. We measured the effect of RLC phosphorylation on Ca2+-activated isometric contraction and myosin cross-bridge kinetics (via stochastic length perturbation analysis) in skinned rat papillary muscle strips at 1.9- and 2.2-µm SL. Maximum tension and Ca2+ sensitivity increased with SL, and RLC phosphorylation augmented this response at 2.2-µm SL. Subtle increases in viscoelastic myocardial stiffness occurred with RLC phosphorylation at 2.2-µm SL, but not at 1.9-µm SL, thereby suggesting that RLC phosphorylation increases β-myosin heavy chain binding or stiffness at longer SLs. The cross-bridge detachment rate slowed as SL increased, providing a potential mechanism for prolonged cross-bridge attachment to augment length-dependent activation of contraction at longer SLs. Length-dependent slowing of β-myosin heavy chain detachment rate was not affected by RLC phosphorylation. Together with our previous studies, these data suggest that both α- and β-myosin heavy chain isoforms show a length-dependent activation response and prolonged myosin attachment as SL increases in rat myocardial strips, and that RLC phosphorylation augments length-dependent activation at longer SLs. In comparing cardiac isoforms, however, we found that β-myosin heavy chain consistently showed greater length-dependent sensitivity than α-myosin heavy chain. Our work suggests that RLC phosphorylation is a vital contributor to the regulation of myocardial contractility in both cardiac myosin heavy chain isoforms.

Myosin light chain replacement in the heart

2000 ◽  
Vol 279 (3) ◽  
pp. H1355-H1364 ◽  
Author(s):  
Atsushi Sanbe ◽  
James Gulick ◽  
Eric Hayes ◽  
David Warshaw ◽  
Hanna Osinska ◽  
...  
Keyword(s):  
Myosin Heavy Chain ◽  
Heavy Chain ◽  
Light Chain ◽  
Myosin Light Chain ◽  
Complete Replacement ◽  
Myosin Heavy Chain Isoform ◽  
Hypertrophic Response ◽  
Force Development ◽  
Cross Bridge ◽  
Systolic And Diastolic Function

Myosin-actin cross-bridge kinetics are an important determinant for cardiac systolic and diastolic function. We compared the effects of myosin light chain substitutions on the ability of the fibers to contract in response to calcium and in their ability to produce power. Transgenesis was used to effect essentially complete replacement of the target contractile protein isoform specifically in the heart. Atrial and ventricular fibers derived from the various transgenic (TG) lines were skinned, and the force-velocity relationships, unloaded shortening velocities, and Ca2+-stimulated Mg2+-ATPase activities were determined. Replacement with an ectopic isoform resulted in significant changes in cross-bridge cycling kinetics but without any overt effects on morbidity or mortality. To confirm that this result was not light chain specific, a modified α-myosin heavy chain isoform that resulted in significant changes in force development was also engineered. The animals appeared healthy and have normal lifespans, and the changes in force development did not result in significant remodeling or overt hypertrophy. We conclude that myosin light chains can control aspects of cross-bridge cycling and alter force development. The myosin heavy chain data also show that changes in the kinetics of force development and power output do not necessarily lead to activation of the hypertrophic response or significant cardiac remodeling.

Selected Contribution: Improved anoxic tolerance in rat diaphragm following intermittent hypoxia

2001 ◽  
Vol 90 (6) ◽  
pp. 2508-2513 ◽  
Author(s):  
Thomas L. Clanton ◽  
Valerie P. Wright ◽  
Peter J. Reiser ◽  
Paul F. Klawitter ◽  
Nanduri R. Prabhakar
Keyword(s):  
Myosin Heavy Chain ◽  
Heavy Chain ◽  
Intermittent Hypoxia ◽  
Contractile Function ◽  
Myosin Heavy Chain Isoforms ◽  
Adaptive Responses ◽  
Low Frequencies ◽  
Myosin Heavy Chain Isoform ◽  
Obstructive Sleep

Intermittent hypoxia (IH), associated with obstructive sleep apnea, initiates adaptive physiological responses in a variety of organs. Little is known about its influence on diaphragm. IH was simulated by exposing rats to alternating 15-s cycles of 5% O2 and 21% O2 for 5 min, 9 sets/h, 8 h/day, for 10 days. Controls did not experience IH. Diaphragms were excised 20–36 h after IH. Diaphragm bundles were studied in vitro or analyzed for myosin heavy chain isoform composition. No differences in maximum tetanic stress were observed between groups. However, peak twitch stress ( P < 0.005), twitch half-relaxation time ( P < 0.02), and tetanic stress at 20 or 30 Hz ( P < 0.05) were elevated in IH. No differences in expression of myosin heavy chain isoforms or susceptibility to fatigue were seen. Contractile function after 30 min of anoxia (95% N2-5% CO2) was markedly preserved at all stimulation frequencies during IH and at low frequencies after 15 min of reoxygenation. Anoxia-induced increases in passive muscle force were eliminated in the IH animals ( P < 0.01). These results demonstrate that IH induces adaptive responses in the diaphragm that preserve its function in anoxia.

scholarly journals Mavacamten Decreases Maximal Force and Ca2+-sensitivity in the N47K-Myosin Regulatory Light Chain Mouse Model of Hypertrophic Cardiomyopathy

2020 ◽  
Author(s):  
Peter O Awinda ◽  
Marissa Watanabe ◽  
Yemeserach M. Bishaw ◽  
Anna M Huckabee ◽  
Keinan B Agonias ◽  
...  
Keyword(s):  
Heart Disease ◽  
Hypertrophic Cardiomyopathy ◽  
Light Chain ◽  
Isometric Force ◽  
Regulatory Light Chain ◽  
Isometric Tension ◽  
Myosin Regulatory Light Chain ◽  
Cardiac Myosin ◽  
Cross Bridge ◽  
Obstructive Hypertrophic Cardiomyopathy

Morbidity and mortality associated with heart disease is a growing threat to the global population and novel therapies are needed. Mavacamten (formerly called MYK-461) is a small molecule that binds to cardiac myosin and inhibits myosin ATPase. Mavacamten is currently in clinical trials for the treatment of obstructive hypertrophic cardiomyopathy (HCM), and it may provide benefits for treating other forms of heart disease. We investigated the effect of mavacamten on cardiac muscle contraction in two transgenic mouse lines expressing the human isoform of cardiac myosin regulatory light chain (RLC) in their hearts. Control mice expressed wild-type RLC (WT-RLC), and HCM mice expressed the N47K RLC mutation. In the absence of mavacamten, skinned papillary muscle strips from WT-RLC mice produced greater isometric force than strips from N47K mice. Adding 0.3 µM mavacamten decreased maximal isometric force and reduced Ca2+-sensitivity of contraction for both genotypes, but this reduction in pCa50 was nearly twice as large for WT-RLC vs. N47K. We also used stochastic length-perturbation analysis to characterize cross-bridge kinetics. The cross-bridge detachment rate was measured as a function of [MgATP] to determine the effect of mavacamten on myosin nucleotide handling rates. Mavacamten increased the MgADP release and MgATP binding rates for both genotypes, thereby contributing to faster cross-bridge detachment, which could speed myocardial relaxation during diastole. Our data suggest that mavacamten reduces isometric tension and Ca2+-sensitivity of contraction via decreased strong cross-bridge binding. Mavacamten may become a useful therapy for patients with heart disease, including some forms of HCM.

Impact of β-myosin heavy chain isoform expression on cross-bridge cycling kinetics

2005 ◽  
Vol 288 (2) ◽  
pp. H896-H903 ◽  
Author(s):  
Veronica L. M. Rundell ◽  
Vlasios Manaves ◽  
Anne F. Martin ◽  
Pieter P. de Tombe
Keyword(s):  
Myosin Heavy Chain ◽  
Heavy Chain ◽  
Atp Hydrolysis ◽  
High Strain ◽  
Male Rats ◽  
Tension Development ◽  
Myosin Heavy Chain Isoform ◽  
Cross Bridge ◽  
Wide Range ◽  
Tension Cost

Myosin heavy chain (MHC) isoforms α and β have intrinsically different ATP hydrolysis activities (ATPase) and therefore cross-bridge cycling rates in solution. There is considerable evidence of altered MHC expression in rodent cardiac disease models; however, the effect of incremental β-MHC expression over a wide range on the rate of high-strain, isometric cross-bridge cycling is yet to be ascertained. We treated male rats with 6-propyl-2-thiouracil (PTU; 0.8 g/l in drinking water) for short intervals (6, 11, 16, and 21 days) to generate cardiac MHC patterns in transition from predominantly α-MHC to predominantly β-MHC. Steady-state calcium-dependent tension development and tension-dependent ATP consumption (tension cost; proportional to cross-bridge cycling) were measured in chemically permeabilized (skinned) right ventricular muscles at 20°C. To assess dynamic cross-bridge cycling kinetics, the rate of force redevelopment ( ktr) was determined after rapid release-restretch of fully activated muscles. MHC isoform content in each experimental muscle was measured by SDS-PAGE and densitometry. α-MHC content decreased significantly and progressively with length of PTU treatment [68 ± 5%, 58 ± 4%, 37 ± 4%, and 27 ± 6% for 6, 11, 16, and 21 days, respectively; P < 0.001 (ANOVA)]. Tension cost decreased, linearly, with decreased α-MHC content [6.7 ± 0.4, 5.6 ± 0.5, 4.0 ± 0.4, and 3.9 ± 0.3 ATPase/tension for 6, 11, 16, and 21 days, respectively; P < 0.001 (ANOVA)]. Likewise, ktr was significantly and progressively depressed with length of PTU treatment [11.1 ± 0.6, 9.1 ± 0.5, 8.2 ± 0.7, and 6.2 ± 0.3 s−1 for 6, 11, 16, and 21 days, respectively; P < 0.05 (ANOVA)] Thus cross-bridge cycling, under high strain, for α-MHC is three times higher than for β-MHC. Furthermore, under isometric conditions, α-MHC and β-MHC cross bridges hydrolyze ATP independently of one another.

scholarly journals Identification of sequences necessary for the association of cardiac myosin subunits.

1991 ◽  
Vol 113 (3) ◽  
pp. 585-590 ◽  
Author(s):  
E M McNally ◽  
M M Bravo-Zehnder ◽  
L A Leinwand
Keyword(s):  
Myosin Heavy Chain ◽  
Heavy Chain ◽  
Light Chain ◽  
Myosin Light Chain ◽  
Carboxyl Terminus ◽  
Amino Terminus ◽  
Cardiac Myosin ◽  
Amino Acid Region ◽  
Myosin Subunits ◽  
Acid Region

To begin to understand the nature of myosin subunit assembly, we determined the region of a vertebrate sarcomeric myosin heavy chain required for binding of light chain 1. We coexpressed in Escherichia coli segments of the rat alpha cardiac myosin heavy chain which spanned the carboxyl terminus of subfragment 1 and the amino terminus of subfragment 2 with a full-length rat cardiac myosin light chain 1. A 16 amino acid region of the myosin heavy chain (residues 792-808) was shown to be required for myosin light chain 1 binding in an immunoprecipitation assay.

scholarly journals Electrophoretic separation and quantitation of cardiac myosin heavy chain isoforms in eight mammalian species

1998 ◽  
Vol 274 (3) ◽  
pp. H1048-H1053 ◽  
Author(s):  
Peter J. Reiser ◽  
William O. Kline
Keyword(s):  
Skeletal Muscle ◽  
Sample Preparation ◽  
Myosin Heavy Chain ◽  
Heavy Chain ◽  
Mammalian Species ◽  
Myosin Heavy Chain Isoforms ◽  
Glycerol Concentration ◽  
Cardiac Myosin ◽  
Homogenization Step

A protocol for sample preparation and gel electrophoresis is described that reliably results in the separation of the α- and β-isoforms of cardiac myosin heavy chain (MHC-α and MHC-β) in eight mammalian species. The protocol is based on a simple, nongradient denaturing gel. The magnitude of separation of MHC-α and MHC-β achieved with this protocol is sufficient for quantitative determination of the relative amounts of these two isoforms in mouse, rat, guinea pig, rabbit, canine, pig, baboon, and human myocardial samples. The sensitivity of the protocol is sufficient for the detection of MHC isoforms in samples at least as small as 1 μg. The glycerol concentration in the separating gel is an important factor for successfully separating MHC-α and MHC-β in myocardial samples from different species. The effect of sample load on MHC-α and MHC-β band resolution is illustrated. The results also indicate that inclusion of a homogenization step during sample preparation increases the amount of MHC detected on the gel for cardiac samples to a much greater extent than for skeletal muscle samples. Although the protocol described in this study is excellent for analyzing cardiac samples, it should be noted that the same protocol is not optimal for separating MHC isoforms expressed in skeletal muscle, as is illustrated.

Single-fiber myosin heavy chain polymorphism: how many patterns and what proportions?

2003 ◽  
Vol 285 (3) ◽  
pp. R570-R580 ◽  
Author(s):  
Vincent J. Caiozzo ◽  
Michael J. Baker ◽  
Karen Huang ◽  
Harvey Chou ◽  
Ya Zhen Wu ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Myosin Heavy Chain ◽  
Heavy Chain ◽  
Muscle Fibers ◽  
Myosin Heavy Chain Isoforms ◽  
Single Fiber ◽  
Myosin Heavy Chain Isoform ◽  
Skeletal Muscle Fibers ◽  
Velocity Relationship ◽  
Force Velocity

Previous studies have reported the existence of skeletal muscle fibers that coexpress multiple myosin heavy chain isoforms. These surveys have usually been limited to studying the polymorphic profiles of skeletal muscle fibers from a limited number of muscles (i.e., usually <4). Additionally, few studies have considered the functional implications of polymorphism. Hence, the primary objective of this study was to survey a relatively large number of rat skeletal muscle/muscle regions and muscle fibers ( n≈ 5,000) to test the hypothesis that polymorphic fibers represent a larger fraction of the total pool of fibers than do so-called monomorphic fibers, which express only one myosin heavy chain isoform. Additionally, we used Hill's statistical model of the force-velocity relationship to differentiate the functional consequences of single-fiber myosin heavy chain isoform distributions found in these muscles. The results demonstrate that most muscles and regions of rodent skeletal muscles contain large proportions of polymorphic fibers, with the exception of muscles such as the slow soleus muscle and white regions of fast muscles. Several muscles were also found to have polymorphic profiles that are not consistent with the I↔IIA↔IIX↔IIB scheme of muscle plasticity. For instance, it was found that the diaphragm muscle normally contains I/IIX fibers. Functionally, the high degree of polymorphism may 1) represent a strategy for producing a spectrum of contractile properties that far exceeds that simply defined by the presence of four myosin heavy chain isoforms and 2) result in relatively small differences in function as defined by the force-velocity relationship.

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