Cyclosporin A-Sensitive Decrease in the Transmembrane Potential across the Inner Membrane of Liver Mitochondria Induced by Low Concentrations of Fatty Acids and Ca²⁺

Abstract

At low Ca²⁺ concentrations the pore of the inner mitochondrial membrane can open in substates with lower permeability (Hunter, D. R., and Haworth, R. A. (1979) Arch. Biochem. Biophys., 195, 468-477). Recently, we showed that Ca²⁺ loading of mitochondria augments the cyclosporin A-dependent decrease in transmembrane potential (ΔΨ) across the inner mitochondrial membrane caused by 10 μM myristic acid but does not affect the stimulation of respiration by this fatty acid. We have proposed that in our experiments the pore opened in a substate with lower permeability rather than in the “classic” state (Bodrova, M. E., et al. (2000) IUBMB Life, 50, 189-194). Here we show that under conditions lowering the probability of “classic pore” opening in Ca²⁺-loaded mitochondria myristic acid induces the cyclosporin A-sensitive ΔΨ decrease and mitochondrial swelling more effectively than uncoupler SF6847 does, though their protonophoric activities are equal. In the absence of P_i and presence of succinate and rotenone (with or without glutamate) cyclosporin A either reversed or only stopped ΔΨ decrease induced by 5 μM myristic acid and 5 μM Ca²⁺. In the last case nigericin, when added after cyclosporin A, reversed the ΔΨ decrease, and the following addition of EGTA produced only a weak (if any) ΔΨ increase. In P_i-containing medium (in the presence of glutamate and malate) cyclosporin A reversed the ΔΨ decrease. These data show that the cyclosporin A-sensitive decrease in ΔΨ by low concentrations of fatty acids and Ca²⁺ cannot be explained by specific uncoupling effect of fatty acid. We propose that: 1) low concentrations of Ca²⁺ and fatty acid induce the pore opening in a substate with a selective cation permeability, and the cyclosporin A-sensitive ΔΨ decrease results from a conversion of ΔΨ to pH gradient due to the electrogenic cation transport in mitochondria; 2) the ADP/ATP-antiporter is involved in this process; 3) higher efficiency of fatty acid compared to SF6847 in the Ca²⁺-dependent pore opening seems to be due to its interaction with the nucleotide-binding site of the ADP/ATP-antiporter and higher affinity of fatty acids to cations.