title: Effects of different expression and posttranslational modifications of myosin light chains on contractility of skinned human cardiac fibers.
abstract: In the human ventricle two isoforms of the phosphorylatable myosin light chain (MPLC) are expressed. These two forms are designated with increasing acidity as LC-2 and LC-2*. In the normal human heart the relation between LC-2/LC-2*-expression is 70/30, suggesting the existence of three different myosin isoenzymes (MPLC-polymorphism) in the normal human ventricle. Both ventricular MPLC-isoforms are monophosphorylated, the LC-2 being higher phosphorylated than the LC-2*. In some patients with heart failure both MPLC isoforms were found to be completely dephosphorylated. In the human atrium a MPLC isoform is expressed which is different from the ventricular MPLC isoforms. The atrial MPLC isoform is mono- and diphosphorylated. Mono-phosphorylation of both the ventricular MPLC isoforms and the atrial MPLC isoform increased responsiveness as well as sensitivity of isometric tension generation of skinned fibers to Ca2+. Part of this effect could be explained by changing the cross-bridge-cycling rate: MPLC increased fapp, the rate-constant for the transition of cross-bridges from the non-force into the force-generating state, thus increasing the amount of force-generating cross-bridge states at a given [Ca2+]. Monophosphorylation of the MPLC isoforms did not change maximal shortening velocity.
authors.affiliation: II. Physiologisches Institut, Universität Heidelberg, FRG.
authors.forename: I
authors.initials: I
authors.lastname: Morano
mesh_terms: D000818:Animals; D006325:Heart Atria / Q000378:metabolism*; D006329:Heart Conduction System / Q000502:physiology*; D006801:Humans; D007700:Kinetics; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism*; D015879:Myosin Subfragments / Q000737:chemistry / Q000502:physiology*; D009218:Myosins / Q000502:physiology; D010766:Phosphorylation; D051381:Rats; D013552:Swine
chemical_list: D015879:Myosin Subfragments; D009218:Myosins