IMPAIRMENT OF MITOCHONDRIAL OXIDATION BY CHLORAMPHENICOL

Abstract

To investigate the acute effects of CHL on energy metabolism we have studied its effects on oxidative activity in isolated mitochondria from adult rat and newborn pig hearts. We have previously shown acutely reduced myocardial function in newborn pig hearts in the presence of CHL. Respiratory substrates provided were pyruvate(PYR)/malate(MAL) 7.1/4.7mM, glutamate(GLU) 18mM, durohydroquinone(DHQ) 1.62mM, α-ketoglutarate(AKG) 5mM, and succinate(SUC) 10mM. State 3(ADP-stimulated) oxidation of PYR, MAL, GLU, and DHQ was unaffected or only mildly affected in the presence of CHL concentrations as high as 500 μg/ml. Oxidation of AKG and SUC was inhibited 39 and 55% respectively in rat and to a similar degree in pig heart by 50 μg/ml CHL. State 4 oxidation was relatively unaffected. SUC oxidation was also observed in sonicated mitochondria and was unaffected by CHL, suggesting that transport was the limiting factor in SUC oxidation. Measurement of SUC accumulation in mitochondria showed transport to be reduced 75-84% in the presence of CHL (500 μg/ml). Studies in the presence of phthalonate indicated that succinate is primarily transported by the AKG carrier in the heart. CHL also inhibited mitochondrial AKG release in the presence of MAL and GLU indicating impairment of the malate/aspartate shuttle by CHL. Impairment of the malate/aspartate shuttle resulting from inhibition of the AKG carrier may contribute to the acute clinical toxicity of CHL.