CORRELATED EXPRESSION OF ATRIAL MYOSIN HEAVY-CHAIN AND REGULATORY LIGHT CHAIN ISOFORMS WITH PRESSURE OVERLOAD HYPERTROPHY IN THE NONHUMAN PRIMATE

Objective: The aim was to determine the extent to which myosin heavy chain and light chain isoform transitions in atrial myocardium are coordinately regulated under pathological conditions in tissue from normal baboons, hypertensive baboons with myocardial hypertrophy, and baboons in which hypertrophy had regressed. Methods: Quantitative distributions of myosin heavy chain (MHC) and regulatory myosin light chain (MLC2) isoforms in atrial myocardium from 35 adult baboons were determined by electrophoresis under denaturing conditions and laser densitometry. Results: A significant association was observed between the ratios of MHC and MLC2 isoforms in atrial myocardium (r=0.73, p<0.001, n=69). Expressions of alpha MHC and atrial MLC2 (ALC2) isoforms were correlated in atrial myocardium, as were those of beta MHC and ventricular MLC2 (VLC2) isoforms. In a subset of baboons with experimentally induced renal hypertension (n=12) both beta MHC and VLC2 isoforms were found at higher levels in left atria than were present in normotensive baboons (p=0.006, n=15). Left atria from hypertensive baboons with regressed LVH contained intermediate levels of both beta MHC and VLC2 isoforms. Conclusions: There is tight coupling between the expression of myosin subunit isoforms under pathological conditions from a primate species closely related to humans. The data suggest that the synthesis of these subunits of myosin may be coordinated at the molecular level.