The nature of mitochondrial respiration and discrimination between membrane and pump properties.
A new criterion is utilized for the interpretation of flow-force relationships in rat liver mitochondria. The criterion is based on the view that the nature of the relationship between the H+/O ratio and the membrane potential can be inferred from the relationship between ohmic-uncoupler-induced extra respiration and the membrane potential. Thus a linear relationship between extra respiration and membrane potential indicates unequivocally the independence of the H+/O ratio from the membrane potential and the leak nature of the resting respiration [Brand, Chien, and Diolez (1994) Biochem. J. 297, 27-29]. On the other hand, a non-linear relationship indicates that the H+/O ratio is dependent on the membrane potential. The experimental assessment of this relationship in the presence of an additional ohmic leak, however, is rendered difficult by both the uncoupler-induced depression of membrane potential and the limited range of dependence of the H+/O ratio on the membrane potential. We have selected conditions, i.e. incubation of mitochondria at low temperatures, where the extent of non-linearity is markedly increased. It appears that the nature of the resting respiration of mitochondria in vitro is markedly dependent on the temperature: at low temperatures the percentage of resting respiration due to membrane leak decreases and that due to intrinsic uncoupling of the proton pumps increases.
Canton
M
M
C.N.R. Unit for the Study of Physiology of Mitochondria, University of Padova, Italy.
Luvisetto
S
S
Schmehl
I
I
Azzone
G F
GF
D000818:Animals; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D003198:Computer Simulation; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D008962:Models, Theoretical; D010101:Oxygen Consumption / Q000187:drug effects; D017494:Proton Pumps / Q000378:metabolism*; D051381:Rats; D013696:Temperature
D017494:Proton Pumps; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone