Cellular and molecular mechanisms of systolic and diastolic dysfunction in an avian model of dilated cardiomyopathy.

We investigated the cellular and molecular mechanisms of systolic and diastolic dysfunction in a furazolidone (Fz)-induced model of dilated cardiomyopathy (DCM) in turkey poults. Serial echocardiograms disclosed marked systolic dysfunction in the Fz-treated poults, and ventricular weight and left ventricular (LV)/body weight ratio were significantly increased. Isolated heart experiments were performed to determine LV pressure-volume (P-V) relationships. In addition, LV sarcomere lengths (SLs) were measured after hearts had been fixed, and wall stress (sigma)-SL relationships were determined. When compared to control hearts, LV chamber volume in DCM hearts was approximately 3-fold increased, the active or developed LV P-V relationship was markedly depressed, the passive or diastolic P-V relationship was steeper, and SLs were significantly shorter. However, the developed sigma-SL relationships of DCM and control hearts were not different indicating that intrinsic myocardial capacity to generate active force is unaffected in this model of DCM. In contrast, passive sigma, and passive tension in trabecular muscle preparations increased much more steeply with SL in DCM than normal hearts. Trabecular muscle experiments disclosed that the increase in passive myocardial stiffness was primarily collagen based. Titin, the giant sarcomeric molecule, which is an important determinant of passive myocyte properties in normal myocardium, did not contribute significantly to increased passive myocardial stiffness in DCM. We conclude that increased collagen-based passive myocardial stiffness is the major cause of the steeper passive or diastolic P-V relationship in DCM. Further, altered passive myocardial properties and ventricular geometry in DCM play a critical role to reduce ventricular systolic function by limiting SL extension during diastole, thereby limiting the use of the myocardial length-tension relationship.