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Uncoupling effect of the general anesthetic 2,6-diisopropylphenol in isolated rat liver mitochondria
D Branca1, M S Roberti, E Vincenti
1Dipartimento di Chimica Biologica, Università di Padova, Italy.
Abstract:
2,6-Diisopropylphenol, a general anesthetic, was previously reported to reduce the transmembrane electrical potential in isolated rat liver mitochondria without affecting the rate of ATP production. This effect appeared to contrast with the generally accepted chemiosmotic mechanism for oxidative phosphorylation. In this study we further examined the influence of 2,6-diisopropylphenol on the production of ATP by isolated mitochondria and we studied its effect on the permeability of the inner mitochondrial membrane to protons. In order to clarify the effects of 2,6-diisopropylphenol on mitochondrial ATP production the activities of the adenine nucleotide translocator and the ATP synthetase were evaluated. The results obtained indicate that the depression of the transmembrane electrical potential elicited by 2,6-diisopropylphenol decreased the activity of the ATP synthetase (as expected in the chemiosmotic model for energy coupling), but not that of the adenine nucleotide translocator. The decrease of the ATP synthetase activity, however, did not result in an apparent inhibition of the overall rate of ATP production in isolated mitochondria due to the rate-limiting effect of the adenine nucleotide translocator in this process. Moreover 2,6-diisopropylphenol was found to increase the permeability to protons of the inner mitochondrial membrane; this effect became more marked as the pH of the incubation medium was increased, demonstrating that it involved the dissociated form of 2,6-diisopropylphenol. These observations suggested that 2,6-diisopropylphenol affected oxidative phosphorylation by acting as a mild protonophore and that its effectiveness was limited by the low fraction of phenol dissociated at near-physiological pH.
Insights
2,6-Diisopropylphenol acts as a protonophore, increasing inner mitochondrial membrane permeability. This anesthetic affects ATP production by influencing ATP synthetase activity, but its overall impact is limited by the adenine nucleotide translocator.
Area of Science:
- Biochemistry
- Mitochondrial Physiology
- Anesthesiology
Background:
- 2,6-Diisopropylphenol, a general anesthetic, was previously shown to reduce mitochondrial transmembrane electrical potential without altering ATP production.
- This observation appeared inconsistent with the established chemiosmotic mechanism of oxidative phosphorylation.
Purpose of the Study:
- To further investigate the effects of 2,6-diisopropylphenol on mitochondrial ATP production.
- To determine its impact on the inner mitochondrial membrane's proton permeability.
- To elucidate the mechanisms underlying its influence on oxidative phosphorylation.
Main Methods:
- Evaluation of adenine nucleotide translocator and ATP synthetase activities in isolated mitochondria.
- Assessment of inner mitochondrial membrane permeability to protons.
- Analysis of 2,6-diisopropylphenol's effects across varying pH conditions.
Main Results:
- 2,6-Diisopropylphenol decreased ATP synthetase activity, consistent with the chemiosmotic model, but did not affect the adenine nucleotide translocator.
- The overall rate of ATP production was not inhibited due to the rate-limiting role of the adenine nucleotide translocator.
- The anesthetic increased inner mitochondrial membrane proton permeability, with increased effect at higher pH, indicating involvement of the dissociated form.
Conclusions:
- 2,6-Diisopropylphenol functions as a mild protonophore, increasing mitochondrial proton permeability.
- Its impact on ATP production is modulated by the adenine nucleotide translocator's rate-limiting function.
- The anesthetic's effectiveness is constrained by its low dissociation at physiological pH.