title: Effects of total replacement of atrial myosin light chain-2 with the ventricular isoform in atrial myocytes of transgenic mice.
abstract: BACKGROUND
  In contrast to their well-known and critical role in excitation-contraction coupling of vascular smooth muscle, the effects of the myosin light chains on cardiomyocyte mechanics are poorly understood. Accordingly, we designed the present experiment to define the cardiac chamber-specific functional effects of the ventricular isoform of the regulatory myosin light chain (MLC2v).
  
  
  RESULTS
  Postnatal transgenic cardiac-specific overexpression of MLC2v was achieved by use of the alpha-myosin heavy chain promoter. Enzymatically disaggregated atrial and ventricular mouse myocytes were field-stimulated at multiple frequencies, and mechanical properties and calcium kinetics were studied by use of video edge detection and FURA 2-AM, respectively. MLC2v overexpression resulted in complete replacement of the atrial with the ventricular isoform of the regulatory myosin light chain at the steady-state mRNA and protein levels in the atria of transgenic mice. Mechanical properties of transgenic atrial myocytes were enhanced to the level of ventricular myocytes of control animals in association with modest decreases in the amplitude of the calcium transient.
  
  
  CONCLUSIONS
  MLC2v modulates chamber-specific contractility by enhanced calcium sensitivity and/or improved cross-bridge cycling of the thin and thick filaments of the cardiomyocyte.
authors.affiliation: Department of Medicine, University of Cincinnati Medical Center, Ohio, USA.
authors.forename: C M
authors.initials: CM
authors.lastname: Pawloski-Dahm
authors.forename: G
authors.initials: G
authors.lastname: Song
authors.forename: D L
authors.initials: DL
authors.lastname: Kirkpatrick
authors.forename: J
authors.initials: J
authors.lastname: Palermo
authors.forename: J
authors.initials: J
authors.lastname: Gulick
authors.forename: G W
authors.initials: GW
authors.lastname: Dorn
authors.forename: J
authors.initials: J
authors.lastname: Robbins
authors.forename: R A
authors.initials: RA
authors.lastname: Walsh
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D024722:Cardiac Myosins; D048429:Cell Size; D005260:Female; D015870:Gene Expression; D006325:Heart Atria / Q000737:chemistry / Q000166:cytology; D006352:Heart Ventricles / Q000737:chemistry / Q000166:cytology; D007527:Isoenzymes / Q000235:genetics*; D007700:Kinetics; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D009119:Muscle Contraction / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000737:chemistry* / Q000201:enzymology; D009206:Myocardium / Q000737:chemistry* / Q000166:cytology / Q000201:enzymology; D018994:Myosin Light Chains / Q000235:genetics*
chemical_list: D007527:Isoenzymes; D018994:Myosin Light Chains; C107184:myosin light chain 2; D024722:Cardiac Myosins; D002118:Calcium