Energy transduction in the myocardial contractile protein system under normal conditions and in toxi-allergic myocarditis.

Energy transduction in purified myocardial myofibrils from normal rabbits and those having toxi-allergic myocarditis (TAM) was compared. In TAM a sharp decrease in the rate and value of ATP hydrolysis enthalpy released during free contraction of myofibrils takes place, and is accompanied by a rise in the amount of energy dissipated as heat. It is concluded that, at the early stages of shrinkage force generation during myofibril contraction in TAM, a breakdown of actin activation of Mg(2+)-ATPase activity for myosin occurs, the character of the bonds is changed, and the efficiency of myosin cross-bridge interaction with the protomeres of the actin thin filaments is decreased. The contractile process becomes wasteful.