Key result
In rabbit hearts, pressure overload increases V3 myosin and isometric contraction economy, whereas thyrotoxicosis increases V1 myosin and cross-bridge cycling frequency.
Myocardial myosin isoenzyme composition (V1 vs V3) dictates the economy of isometric contraction and cross-bridge cycling dynamics in hypertrophied rabbit hearts.
Does not support changes in clinical practice; leaves open myosin isoform effects on human hypertrophy energetics.
This is a review of work dealing with the contribution of myocardial myosin isoenzymes to the performance of the heart muscle. Isoenzyme composition is altered in rabbit hearts by banding the pulmonary artery (increase in %V3) and thyroid hormone injection (increase in V1). Both treatments result in myocardial hypertrophy. The performance of the hearts rich in V3 or V1 myosin isoenzyme is assessed by simultaneous analysis of the myothermal and mechanical output of papillary muscles isolated from the right ventricle. Initial and tension dependent heart per tension time integral are decreased in the pressure overload and increased in the thyrotoxic hypertrophied hearts. Thus, the economy of isometric contraction is high in the hearts with the V3 myosin and low in the hearts with the V1 myosin. This change in performance is explained in terms of alterations in the cycling frequency and tension time integral of the myosin cross-bridge. In the pressure overload hearts the cross-bridge cycling frequency is decreased, while the tension time integral is increased. Conversely, in the thyrotoxic preparations the cycling frequency is increased and the tension time integral is decreased.
No takes yet. Share an insight, caveat, or question.
Alpert et al. (1986) conducted a review in Myocardial hypertrophy. Altered cardiac myosin isoenzymes (V3 vs V1) was evaluated on Myothermal and mechanical output of papillary muscles. In rabbit hearts, pressure overload increases V3 myosin and isometric contraction economy, whereas thyrotoxicosis increases V1 myosin and cross-bridge cycling frequency.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: