Inhibitory uncouplers permeability

The permeability of chloroplast membranes to endogenous K" " was also increased by FCCP and the inhibitory uncouplers, but not... 

The inhibitory uncouplers, but not diuron and 2,3-DCIPC, also altered the permeability to protons of artificial, purely lipoidal, liposome membranes. In the system (Figure 3A), electrons flow... 

Fig. 10.6. The effect of respiration and membrane potential (Ai )) on Cl permeation in brown adipose tissue mitochondria. When brown fat mitochondria were incubated in KCl in the presence of the ionophore, nigericin, they swelled (A, B). If a respiratory substrate (here G-3-P glycerol-3-phosphate) was added to the expanded mitochondria, they contracted, and this contraction ceased immediately and swelling was reintroduced if azide (NaNj) and an uncoupler (FCCP) were added (Fig. A). The passive halide ion permeability can be inhibited by GDP (cf.. Fig. 10.5), but respiration-driven contraction in KCl-expanded mitochondria was only partially inhibited by the presence of GDP (Fig. B) if again azide and uncoupler were added during the contraction, the mitochondria did not swell, indicating that the thermogenin channel was closed by GDP. This behaviour can partly be explained by the fact that the Cl permeation is driven by the membrane potential. Indeed, when, under similar conditions, the rate of contraction was plotted as a function of the membrane potential, it was seen that the rate was membrane potential dependent. It should, however, he noted that at low membrane potentials GDP nearly totally abolished the Cl permeation but when the membrane potential was increased above 30 mV, the inhibitory effect of GDP was apparently partially lost. The basis for this phenomenon is not understood it is not even known if there is a lower affinity of thermogenin for GDP in the energized membrane, as measurements of GDP affinities always refer to the non-energized situation. (Adapted from Nicholls et al. [27] (A, B) and Nicholls [94] (C).)...

Motais, R., Sola, F. and Cousin, J. L. (1978) Uncouplers of oxidative phosphorylation. A structure-activity study of their inhibitory effect on passive chloride permeability. Biochim. Biophys. Acta, 510, 201-7. 

The antimicrobial action of the ionophores is undoubtedly related to their ability to render microbial membranes permeable to ions. They induce the loss of from bacteria and, in many cases their inhibitory action towards them can be reversed by adding K to the medium [189,193]. However, there is considerable disagreement over the way in which ionophores uncouple oxidative phosphorylation. The arguments concern the different concepts of the mechanisms of energy transduction and have received critical appraisal in reviews by Harold [6,174] and Hamilton [175,194]. 

By definition, the uncoupling effect of certain flavonoids should be independent of their inhibitory effects on mitochondrial respiration or FoFi-ATPase, suggesting an additional mode of action of flavonoids against mitochondrial function. A collapse of the transmembrane potential is likely under conditions in which the permeability barrier created by the mitochondrial inner membrane is compromised (as occurs in the presence of ionophores). Calcium, phosphate, oxidative stress, adenine nucleotide depletion, and membrane depolarization can induce such a nonspecific increase in the permeability of the inner membrane, in an event called the mitochondrial permeability transition (MPT) [30,34]. The MPT can be selectively inhibited by cyclosporin A and is believed to involve the assembly of a multiprotein complex to form a nonspecific pore that spans the inner and outer mitochondrial membranes. The latter assembly is referred to as the permeability transition pore complex (PTPC) (Fig. 1). Its exact composition is unknown, but appears to comprise cyclophilin D, ANT, the voltage-dependent anion channel (porin), and a benzodiazepinebinding site [10,30,34]. 

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