We have identified two distinct β-myosin heavy chains (MHCs) present in baboon myocardium by electrophoresis in gradient pore gels and by Western blots with anti-MHC MAb. The two β-MHCs have molecular masses of 210 and 200 kD and share several antigenic determinants including an epitope recognized by a β-MHC-specific MAb. A fivefold increase in the level of the 200-kD β-MHC was observed in the hypertrophied left ventricles of baboons with chronic (5.3 ± 0.7 yr) renal hypertension. A 60% increase (P < 0.01) in BP and a 100% increase (P < 0.001) in left ventricular mass to body weight ratio occurred in hypertensive baboons compared with normotensive animals. The Ca2+-activated myosin ATPase activity in hypertrophied left ventricles was decreased by 35% (P < 0.05) compared with controls. Normal levels of the 200-kD MHC were detected in the right ventricles and intraventricular septa of the hypertensive animals. These data suggest that cardiac MHCs of primates may exist in alternative molecular forms that are indistinguishable by nondenaturing gel electrophoresis and that increased concentration of a second β-MHC is associated with ventricular hypertrophy (r = 0.55). The functional significance and mechanisms that control the concentration of β-MHC subspecies remain to be determined.
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