Mechanisms of Inhibition and Uncoupling of Respiration in Isolated Rat Liver Mitochondria by the General Anesthetic 2,6‐Diisopropylphenol

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Abstract
We investigated the effects of 2,6-diisopropylphenol on oxidative phosphorylation of isolated rat liver mitochondria. Diisopropylphenol strongly inhibits state-3 and uncoupled respiratory rates, when glutamate and malate are the substrates, as a direct consequence of the limitation of electron transfer at the level of complex I. In addition, diisopropylphenol acts as an uncoupler in non-phosphorylating mitochondria, which leads to an increase in respiratory rate and a large decrease in proton-motive force. However, such effects cannot be due to the classical protonophoric property of this drug, since addition of ADP plus oligomycin before diisopropylphenol avoids this increase in proton permeability, and in phosphorylating mitochondria, the ATP/O ratio is not significantly affected by diisopropylphenol addition. In the absence of added ADP, diisopropylphenol modifies some mitochondrial ATPases in such a way that they become insensitive to oligomycin and unable to couple proton movement to ATP synthesis or hydrolysis. However, these modified enzymes can catalyse passive proton permeability, which leads to uncoupling. Addition of ADP before diisopropylphenol prevents these changes. We propose that ADP induces a change in conformation of ATPase, which leads to insensitivity of this complex towards diisopropylphenol. In conclusion, we show that diisopropylphenol has two main effects on rat liver mitochondria: inhibition of the respiratory chain at the level of complex I level and modification of ATPase such that, in the absence of phosphorylation, it catalyses a H+ leak, which becomes negligible when oxidative phosphorylation is functional.