Computational models for monitoring the trans-membrane potential with fluorescent probes: the DiSC3(5) case.

Fluorescent permeant charged probes are commonly used for monitoring the trans-membrane potential in lipid vesicles and biological membranes, which has been earlier described by various mathematical models. In the present study, we developed a more complex model based on the computational step-by-step analysis of the influence of various factors, such as the membrane surface potential, ionic strength, and the aggregation properties of cationic cyanine probe DiSC3(5) in the membrane and aqueous phases, in addition to the Nernstian distribution of the probe across the membrane and the hydrophobic interaction with the lipid bilayer. The final full model allows prediction of the optimal experimental conditions for monitoring the trans-membrane potential, such as the probe/lipid ratio and the concentration of liposomes, with a given percentage of negatively charged phospholipids in the membrane, the ionic strength of the aqueous media, the "membrane-water" partition coefficient and the aggregation properties of the probe, as well as the most adequate mode of fluorescence measurement. In agreement with many experimental studies, this model showed high voltage sensitivity of the quantity of the aqueous phase DiSC3(5) monomers, showing its almost exponential decrease with an increase in the trans-membrane potential value. The model also demonstrated the highest voltage sensitivity of the ratio of the quantity of DiSC3(5) monomers in the aqueous phases to that in the membrane phase. A new combined parameter, the logarithmic function of this ratio, demonstrated almost linear changes within a wide range of the trans-membrane potential changes.

Early hyperglycemia following alloxan administration in vivo is not associated with altered hepatic mitochondrial function: acceptable model for type 1 diabetes?

Alloxan and oxidative stress, which have been detected in livers of laboratory animals shortly after in vivo alloxan administration, cause in vitro mitochondrial dysfunction, thus questioning alloxan diabetes as an acceptable model for type 1 diabetes, a model that cannot legitimately be used to investigate mitochondrial metabolism in a diabetic state. In the current study, the blood glucose concentration increased in the drug-treated group of Sprague-Dawley rats (compared with the placebo group) 45 or 60 min after alloxan treatment, whereas at 30 min the blood glucose concentration was unchanged. State 4, state 3, respiratory control, efficiency of oxidative phosphorylation, and mitochondrial ATP synthase activity, assayed using glutamate plus malate, pyruvate plus malate, or succinate as a substrate, were not negatively altered during the entire study. These results indicated that early increases of blood glucose concentration, after in vivo alloxan administration, did not lead to liver mitochondrial dysfunction, suggesting that alloxan diabetes can be used for the study of liver mitochondrial respiration in a diabetic state.