Trimetazidine: in vitro influence on heart mitochondrial function

The mechanism of action of the antianginal trimetazidine (TMZ) remains largely unknown. In cultured rat ventricular myocytes in physiologic conditions, TMZ (5 x 10(-4) M) reduced the plateau potential level, the upstroke velocity, and the spontaneous action potential rate. When the cardiomyocytes were submitted to hypoxia (150 or 240 minutes) in a glucose-free medium, treatment with TMZ largely prevented the hypoxia-induced electromechanical alterations, i.e., the decrease in plateau amplitude, in resting membrane potential, in action potential duration, in rate, and in contractility. No hypoxia-induced arrhythmia was observed in the TMZ-treated cells. Moreover, the lactate dehydrogenase leakage was significantly reduced in the TMZ-treated cardiomyocytes (-58% and -36%, after 150 and 240 minutes of hypoxia, respectively). The drug was not efficient in reducing the hypoxia-induced decrease in adenosine triphosphate (ATP) content. The cellular ATP content was slightly lower in the TMZ-treated cells in normoxic conditions and in hypoxic conditions, but only in the glucose-free medium. To investigate further the relation between TMZ and energy metabolism, the respiration parameters were measured in heart mitochondria isolated from control and TMZ-treated rats (6 mg/kg/day, 7 days) with different substrates. This treatment resulted in a slight alteration of pyruvate oxidation, which was observed in the absence and in the presence of TMZ (10(-4) M) in the respiration medium. Conversely, a potent inhibition of palmitoylcarnitine oxidation was measured when TMZ was added to the respiration medium. Neither pretreatment of the rats, nor addition of TMZ to the medium affected the oxidation of glutamate or citrate.(ABSTRACT TRUNCATED AT 250 WORDS)