MYOCYTE PERFORMANCE DURING EVOLUTION OF MYOCARDIAL-INFARCTION IN RATS- EFFECTS OF PROPIONYL-L-CARNITINE

To determine whether alterations in the mechanical properties and calc ium transients of myocytes are important factors in the evolution of t he postinfarcted heart, these physiological parameters were measured i n the viable muscle cells of the left ventricle 6 h, 2-3 days, 1 wk, a nd 1 mo after coronary artery occlusion and the documentation of left ventricular failure. In addition, the effects of propionyl-L-carnitine (PLC) on shortening properties and calcium dynamics of single myocyte s were established to demonstrate whether the potential increase in AT P generation by this intervention improved myocyte cell function. Myoc ardial infarction was associated with a progressive increase in length of the spared myocytes, whereas the changes in myocyte diameter were apparent only at the 1-mo interval. Mechanically, myocyte shortening w as decreased 43% at 6 h, 34% at 2-3 days, 26% at 1 wk, and 41% at 1 mo after infarction. Similar abnormalities were noted in the velocity of myocyte shortening. Peak systolic calcium was decreased at all interv als after infarction. In contrast, diastolic calcium remained within c ontrol values. PLC was capable of ameliorating the mechanical behavior and calcium transients of myocytes, particularly 1 mo after infarctio n. Thus alterations in muscle cell performance may be important determ inants in the development and progression of ischemic cardiomyopathy, and interventions improving myocyte contractility may interfere with t he unfavorable outcome of the disease.