MECHANISMS OF INHIBITION AND UNCOUPLING OF RESPIRATION IN ISOLATED RAT-LIVER MITOCHONDRIA BY THE GENERAL ANESTHETIC 2,6-DIISOPROPYLPHENOL

We investigated the effects of 2,6-diisopropylpheno1 on oxidative phos phorylation of isolated rat liver mitochondria. Diisopropylphenol stro ngly inhibits state-3 and uncoupled respiratory rates, when glutamate and malate are the substrates, as a direct consequence of the limitati on of election transfer at the level of complex I. In addition, diisop ropylphenol acts as an uncoupler in non-phosphorylating mitochondria, which leads to an increase in respiratory rate and a large decrease in proton-motive farce. However, such effects cannot be due to the class ical protonophoric property of this drug, since addition of ADP plus o ligomycin before diisopropylphenol avoids this increase in proton perm eability, and in phosphorylating mitochondria, the ATP/O ratio is not significantly affected by diisopropylphenol addition, In the absence o f added ADP, diisopropylphenol modifies some mitochondrial ATPases in such a way that they become insensitive to oligomycin and unable to co uple proton movement to ATP synthesis or hydrolysis, However, these mo dified enzymes can catalyse passive proton permeability, which leads t o uncoupling. Addition of ADP before diisopropylphenol prevents these changes. We propose that ADP induces a change in conformation of ATPas e. which leads to insensitivity of this complex towards diisopropylphe nol. In conclusion, we show that diisopropylphenol has two main effect s on rat liver mitochondria: inhibition of the respiratory chain at th e level of complex I level and modification of ATPase such that, in th e absence of phosphorylation, it catalyses a H+ leak, which becomes ne gligible when oxidative phosphorylation is functional.