Pentachlorobutadienyl-l-cysteine uncouples oxidative phosphorylation by dissipating the proton gradient

A very early event in the toxicity of pentachlorobutadienyl-l-cysteine (PCBC) to rabbit renal proximal tubules is uncoupling of oxidative phosphorylation (R. G. Schnellmann, E. A. Lock, and L. J. Mandel (1986), Toxicologist 6, 176; (1987), Toxicol. Appl. Pharmacol. 90, 521). The mechanism of PCBC uncoupling of mitochondrial oxidative phosphorylation has been investigated using isolated rabbit renal cortical mitochondria (RCM). PCBC increased state 4 respiration of RCM respiring on pyruvate/malate or succinate in a concentration (10-100 μm)- and time (1-5 min)-dependent manner. PCBC also increased state 4 respiration in the presence of oligomycin, an inhibitor of F₀F₁-ATPase. The effect of PCBC on mitochondrial proton permeability was determined by measuring passive mitochondrial swelling. After a 2-min exposure to PCBC, RCM swelled when placed in NH₄Cl or NaCl, but not KCl or sucrose. The protonophore carbonyl cyanide p-trifluoromethoxyphenyl hydrazone (FCCP) (1 μm) produced similar effects. After 5 min, RCM swelled when placed in NH₄Cl, NaCl, or KCl, but not in sucrose. Aminooxyacetic acid, an inhibitor of cysteine conjugate β-lyase, blocked the effects of PCBC on respiration, indicating that PCBC can be metabolized by RCM to produce RCM toxicity. These results show that PCBC initially uncouples oxidative phosphorylation by dissipating the proton gradient. Subsequently, additional ion permeabilities occur. These results are in complete agreement with previous observations in rabbit renal proximal tubule suspensions.