The mechanisms that control cardiac contractility are complex. Recent work we conducted in vertebrate skeletal muscle identified a new state of myosin, the super-relaxed state (SRX), which had a very low metabolic rate. To determine whether this state also exists in cardiac muscle we used quantitative epi-fluorescence to measure single nucleotide turnovers by myosin in bundles of relaxed permea...

Increases in free Mg from 0.04 to 10.0 mM with constant pH 7.0, 0.10 M ionic strength, and 2 m.M MgATP" caused a rightward shift of the free Ca-relative ATPase relation for both cardiac and skeletal myofibrils. The specific activity of cardiac myofibrillar ATPase over a wide range of free Ca was, however, depressed in 0.04 vs. 1.0 mM Mg" , whereas a similar decrease in free Mg r slightly enhanc...

Blebbistatin is a powerful inhibitor of actin-myosin interaction in isolated contractile proteins. To examine whether blebbistatin acts in a similar manner in the organized contractile system of striated muscle, the effects of blebbistatin on contraction of cardiac tissue from mouse were studied. The contraction of paced intact papillary muscle preparations and shortening of isolated cardiomyoc...

A comparative study of myosin light chains (MLCs) has been made in the aorta, uterine and cardiac muscles (auricle, ventricle) of mice, pig, sheep and goat. Analysis of myosin light chains by sodium dodecyl polyacrylamide gel electrophoresis (SDS-PAGE) has revealed that (a) aorta myosin from mice, goat and pig has identical myosin light chains profile but pig aorta myosin lacks LC-2f; (b) uteri...

Smooth muscle contraction differs somewhat from skeletal muscle. Ca is involved in the initiation of contraction as it is in skeletal muscle. However, the myosin in smooth muscle must be phosphorylated for activation of the myosin ATPase. Phosphorylation and dephosphorylation of myosin also occurs in skeletal muscle, but phosphorylation is not necessary for activation of the ATPase. In smooth m...

The substrate, ATP, protects the active site of cardiac myosin during a 10-min treatment at 37 "C and neutral pH in the absence of divalent cations; under these conditions there is an approximate 20 % dissociation of light chain C1 and 60 % loss of light chain CZ with no corresponding decrease in myosin ATPase activity. Higher temperatures, the absence of divalent cations, increased treatment t...

It has long been known that myosin and actin can be obtained from heart as well as from skeletal muscle and that, in combining them to form actomyosin, they are interchangeable with their skeletal counterparts (1). The contractile properties of glycerolextracted cardiac strips and cardiac actomyosin (myosin B) threads and bands have also been demonstrated (2, 3). The molecular parameters of car...