3Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, 194223 St. Petersburg, Russia; fax: (812) 552-7931
* To whom correspondence should be addressed.
Received October 26, 2008; Revision received December 22, 2008
Tetrahymena pyriformis is used in diverse studies as a non-mammalian alternative due to their resemblance in many main metabolic cycles. However, such basic features of mitochondrial energetics as Δψ (electrical potential difference across the inner mitochondrial membrane) or maximal stimulation of respiration by uncouplers with different mechanisms of uncoupling, such as DNP (2,4-dinitrophenol) and FCCP (p-trifluoromethoxycarbonylcyanide phenylhydrazone), have not been studied in living ciliates. Tetrahymena pyriformis GL cells during stationary growth phase after incubation under selected conditions were used in this study. Maximal stimulation of cellular respiration by FCCP was about six-fold, thus the proton motive force was high. The DNP uncoupling effect was significantly lower. This suggests low activity of the ATP/ADP-antiporter, which performs not only exchange of intramitochondrial ATP to extramitochondrial ADP, but also helps in the uncoupling process. It participates by a similar mechanism in electrophoretic transport from matrix to cytosol of ATP4– and DNP anion, but not FCCP anion. Thus, in contrast with mammalian mitochondria, T. pyriformis mitochondria cannot rapidly supply the cytosol with ATP; possibly the cells need high intramitochondrial ATP. The difference between DNP and FCCP is hypothetically explained by low Δψ value and/or an increase in concentration of long-chain acyl-CoAs, inhibitors of the ATP/ADP-antiporter. The first suggestion is confirmed by absence of mitochondria with bright fluorescence in T. pyriformis stained with the Δψ-sensitive probe MitoTracker Red. These data suggest that T. pyriformis cells are useful as a model for study of mitochondrial role in adaptation at the intracellular level.
KEY WORDS: ATP/ADP-antiporter, membrane potential, mitochondria, Tetrahymena pyriformis, uncouplers, DNP, intracellular adaptation