Distribution pattern of α and β myosin in normal and diseased human ventricular myocardium

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Abstract
All fibers in three normal, four dilated, and two ischemic human ventricles were classified according to their myosin content using three sets of monoclonal antibodies each specific for one myosin heavy chain isoform (α, β and β′). Numerous fibers contained only β myosin heavy chain (denoted as β fibers), others contained either α and β, or β and β′ myosin heavy chain (denoted as αβand ββ′ fibers, respectively). The percentages of αβ fibers were systematically determined along the walls of seven homologous regions of the ventricular myocardium. In all ventricles, there was an αβ-fiber transmural gradient, with less αβ fiber in the subendocardium than in the subepicardium. More αβ fibers were found in the right than in the left ventricular wall but there was no difference between the mid-portion and the apex of the free wall of each ventricle. The diseased ventricles contained a lower αβ fiber percentage than the normal hearts. ββ′ fibers were very rare in the normal ventricles (less than 5%) and almost inexistent in pathological hearts. The correlation between the mean αβ fiber percentages of the diseased hearts and their cardiac indices (r=0.88, P<0.05) suggests that the small amount of α myosin distributed in a large number of ventricular fibers could play a role in the contractile performance of the heart. In conclusion, this study provides evidence for 1) an αβ fiber transmural gradient, and 2) a lower α myosin ratio in discased than in normal human ventricle.

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