Skinned fibers of human atrium and ventricle: myosin isoenzymes and contractility.
Different myosin isoenzymes of pig and human atrium and ventricle and rat ventricle were characterized by two approaches: pyrophosphate polyacrylamide gel electrophoresis (PP-PAGE) and analysis of the myosin P light chains by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). We further investigated the relation between atrial and ventricular myosin isoenzymes of human, pig, and rat, and the maximum (unloaded) shortening velocity (Vmax) and the Ca2+ sensitivity of chemically skinned fibers of the same species. The myosin isoenzymes of both human and pig atrium comigrated in the PP-PAGE with rat V2 isomyosin, whereas the ventricle of human and pig comigrated with rat V3. In both human and pig ventricle, a myosin P light chain polymorphism exists (two phosphorylatable P light chains with the same molecular weight but different isoelectric points). In contrast, we found no P light chain polymorphism in the atrium of human and pig and in the ventricle of rat (one phosphorylatable P light chain only). A correlation exists between Vmax, Ca2+ sensitivity, and atrium- and ventricle-specific myosin isoenzymes of human and pig. Vmax was determined by the slack-test method. Plots of delta l versus delta t of atrial and ventricular skinned fibers were well fitted by a single straight line up to delta l = 15% and delta l = 13%, respectively. Vmax of skinned ventricular fibers was lower than Vmax of skinned atrial fibers in both human and pig. Ca2+ sensitivity of skinned fibers of ventricle, however, was higher than Ca2+ sensitivity of atrial skinned fibers in both human and pig.
Morano
I
I
Institute of Physiology II, University of Heidelberg, Federal Republic of Germany.
Arndt
H
H
Gärtner
C
C
Rüegg
J C
JC
D000818:Animals; D002118:Calcium / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D006325:Heart Atria / Q000201:enzymology*; D006352:Heart Ventricles / Q000201:enzymology*; D006801:Humans; D009200:Myocardial Contraction; D009218:Myosins / Q000378:metabolism*; D051381:Rats; D013552:Swine
D009218:Myosins; D002118:Calcium