INHIBITION OF MITOCHONDRIAL RESPIRATION AND OXYGEN-UPTAKE IN ISOLATEDRAT RENAL TUBULAR FRAGMENTS BY ATRACTYLOSIDE

Atractyloside (ATR) is widely used as a specific inhibitor of mitochon drial adenine nucleotide translocase and it is also a potent nephrotox in that selectively injures the proximal tubule in vivo. This regiosel ectivity has been attributed to the prominence of mitochondria in the proximal tubule cells, but there have been no investigations to confir m this. In order to better understand the molecular basis of ATR-induc ed renal injury, oxidative phosphorylation was studied in freshly isol ated rat proximal tubular and glomeruli fragments, and in isolated rat renal cortical mitochondria. In isolated renal mitochondrial, ATR sig nificantly inhibited state 3 respiration in a dose-dependent manner, w ith the maximum inhibition achieved at the highest ATR concentration. Low doses of ATR (53 mu M) inhibited respiration by 50%, an effect whi ch was reversed by 2.5 mu mol ADP. 2,4-Dinitrophenol (5 mM), which sti mulated respiration in control mitochondria, failed to do this in the presence of ATR. Basal oxygen consumption was significantly inhibited by ATR (> 50 mu M) in proximal tubule previously incubated for 1 h at 37 degrees C. The concentration-dependent inhibition of oxygen uptake by the proximal tubule was maintained in the presence of 1 mM ouabain or 0.25 mg/ml nystatin. Glomeruli have active mitochondrial respiratio n (about half that of the proximal tubules), but were not affected by ATR at concentrations up to 500 mu M. These data demonstrates that bot h purified renal mitochondria and freshly isolated fragments of the pr oximal tubule exposed to ATR in vitro exhibit similar alteration in re spiratory parameters that demonstrate inhibition of state 3 mitochondr ial respiration, but there was no significant effect on glomeruli cell s. Thus, the inhibition of oxidative phosphorylation may be an early e vent in ATR-induced nephrotoxicity, where the prominence of mitochondr ia in the proximal tubule explain, in part, the localised injury. The resistance of the glomeruli suggest that preferential transport of ATR may also contribute to the sensitivity of the proximal tubule.