Depressed myocardial cross-bridge cycling kinetics in a female guinea pig model of diastolic heart failure

Diastolic dysfunction was induced in guinea pigs by pressure overload. We found myofilament dysfunction that included depressed force development, reduced tension-dependent ATP consumption rate, prolonged K-tr, and prolonged myofibril relaxation in the absence of a change in myosin isoform composition. Blunted cross-bridge cycle kinetics may be an important contributor to diastolic heart failure. Cardiac hypertrophy is associated with diastolic heart failure (DHF), a syndrome in which systolic function is preserved but cardiac filling dynamics are depressed. The molecular mechanisms underlying DHF and the potential role of altered cross-bridge cycling are poorly understood. Accordingly, chronic pressure overload was induced by surgically banding the thoracic ascending aorta (AOB) in similar to 400 g female Dunkin Hartley guinea pigs (AOB); Sham-operated age-matched animals served as controls. Guinea pigs were chosen to avoid the confounding impacts of altered myosin heavy chain (MHC) isoform expression seen in other small rodent models. In vivo cardiac function was assessed by echocardiography; cardiac hypertrophy was confirmed by morphometric analysis. AOB resulted in left ventricle (LV) hypertrophy and compromised diastolic function with normal systolic function. Biochemical analysis revealed exclusive expression of beta-MHC isoform in both sham control and AOB LVs. Myofilament function was assessed in skinned multicellular preparations, skinned single myocyte fragments, and single myofibrils prepared from frozen (liquid N-2) LVs. The rates of force-dependent ATP consumption (tension-cost) and force redevelopment (K-tr), as well as myofibril relaxation time (Time(lin)) were significantly blunted in AOB, indicating reduced cross-bridge cycling kinetics. Maximum Ca2+ activated force development was significantly reduced in AOB myocytes, while no change in myofilament Ca2+ sensitivity was observed. Our results indicate blunted cross-bridge cycle in a beta-MHC small animal DHF model. Reduced cross-bridge cycling kinetics may contribute, at least in part, to the development of DHF in larger mammals, including humans.

Automated summary

By inducing diastolic dysfunction in guinea pigs through pressure overload, we observed myofilament dysfunction and blunted cross-bridge cycle kinetics, which may contribute to the development of diastolic heart failure. Our findings suggest that altered cross-bridge cycling plays a potential role in diastolic heart failure.