Myofibrillar proteins (MPs) were extracted from isolated and perfused rat hearts subjected to different periods of ischemia to investigate the occurrence of protein degradation and/or the association of cytosolic proteins with the myofibrillar pellet. A 23-kD band was detected by SDS-PAGE of MPs after 5 minutes of ischemia, with its density gradually increasing to a plateau after 20 minutes. Longer periods of ischemia were associated with the appearance of a 39-kD band. Irrespective of the duration of ischemia, both these bands persisted during reperfusion. A partial proteolytic degradation of troponin T (TnT) and troponin I (TnI) has been claimed to be responsible for the generation of these peptides. However, the N-terminal sequence of the 39-kD band was identical to that of GAPDH, whereas Edman sequencing after pepsin digestion showed that the 23 kD is alpha B-crystallin. The binding of the two cytosolic proteins to myofibrils was confirmed by immunofluorescence analysis on cryosections of ischemic hearts. In vitro studies showed that acidosis was sufficient to induce the binding of alpha B-crystallin, whereas the inhibition of ATP depletion prevented the binding of GAPDH. Thiol oxidation is unlikely to promote GAPDH binding, since perfusion with iodoacetate under aerobic conditions or treatment of homogenates with N-ethylmaleimide or diamide failed to induce GAPDH association with the myofibrils. These changes of the myofibrillar proteins could be considered as intracellular markers of the evolution of the ischemic damage. In addition, the binding of the 23-kD peptide might be involved in alterations of contractility.

Propionyl-L-carnitine, unlike L-carnitine, is known to improve myocardial function and metabolism altered during the course of ischemia-reperfusion. In this study, the effect of propionyl-L-carnitine has been compared with that of propionate and carnitine on the performance of rat hearts perfused with a glucose-containing medium either under normoxia, ischemia, or postischemic reperfusion. In the postischemic phase, contractile parameters were partially restored both in the control and in the propionate plus carnitine-treated hearts, were markedly impaired by propionate, and were fully recovered by propionyl-L-carnitine. In addition, propionyl-L-carnitine, but not propionate, reduced the functional decay of mitochondria prepared from the ischemic hearts. Even in normoxic conditions propionate, unlike propionyl-L-carnitine, caused a drastic reduction of free CoA and L-carnitine. The concomitant increase in lactate production and decrease in ATP content might be explained by the inhibition of pyruvate dehydrogenase caused by the accumulation of propionyl-CoA. Indeed, when pyruvate was the only oxidizable substrate, propionate induced a gradual decrease in developed pressure, which was largely prevented by L-carnitine. The protective effect of propionyl-L-carnitine may be a consequence of the anaplerotic utilization of propionate in the presence of an optimal amount of ATP and free L-carnitine.

In patients with intermittent claudication, assessment of plasma acetylcarnitine at rest and after exercise may be a means to select a target population for L-carnitine therapy.

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