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 approachespyrophosphate 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 Al versus At of atrial and ventricular skinned fibers were well fitted by a single straight line up to Δl = 15% and Δl = 13%, respectively. Vmax of skinned ventricular fibers was lower than Vmax of skinned atrial fibers in both human and pig. Ca sensitivity of skinned fibers of ventricle, however, was higher than Ca sensitivity of atrial skinned fibers in both human and pig.