In order to estimate the influence of mitochondrial

In order to estimate the influence of mitochondrial hypo-polarization on generated OMP, IMP was changed from the normal value of Δψi = −140 mV (Fig. 4A, D, G) to Δψi = −100 mV (Fig. 4B, E, H), resulting in lower magnitudes of calculated OMP for hypo-polarized AR 231453 sale (Fig. 4B). Similarly, a remarkable decrease in OMP was observed when the concentration of cytosolic glucose-6-phosphate was increased from 0.15 mM to 1.5 mM, keeping Δψi = −140 mV (Fig. 4C). Only a slight OMP-dependent restriction of the metabolic flux Ics through the contact sites was demonstrated for normal mitochondria (Fig. 4D), although OMP reached relatively high magnitudes (Fig. 4A). An even lower restriction of Ics was observed for hypo-polarized mitochondria (Fig. 4E) and for normal mitochondria in a medium with a higher concentration of glucose-6-phosphate (Fig. 4F). In contrast, the model demonstrated remarkable OMP-dependent restriction of the MOM permeability to Pi− for normal mitochondria (Fig. 4G), a moderate restriction for hypo-polarized mitochondria (Fig. 4H) and a less expressive effect for normal mitochondria in a medium with an enhanced concentration of glucose-6-phosphate (Fig. 4I). As demonstrated in Fig. 3E, F, higher magnitudes of generated OMP were calculated assuming the most profound electrical closure of free VDACs for Pi− (Pc = 0.1 in Eqs. (2), (3)). Another factor favoring OMP generation is VDAC “corking up”, or in general, inhibition of some percentage of free, unbound voltage-sensitive VDACs in MOM [30]. For the following estimations, the fraction of the “corked up” VDACs was changed in a range of up to 30% of all VDACs. High magnitudes of OMP were calculated beginning from “corking up” of more than 20% of all VDACs in MOM for mitochondria with only 4% of VDACs forming ANT-VDAC1-HKI contact sites, at Δψi = −140 mV, Pc = 0.1, VDAC3 fraction NV3 = 0.15 (15%), 0.15 mM glucose-6-phosphate and the voltage sensitivity parameter S = 30 V−1 (Fig. 5A). At higher VDAC voltage sensitivity, S = 40 V−1, a sharp glucose-dependent increase in OMP was demonstrated under the same conditions even without any “corking up” of VDACs (Fig. 5B). Only small values of OMP were obtained for the case of zero VDAC voltage sensitivity, S = 0 V−1 (Fig. 5D). It should be noted that a very slight OMP-dependent restriction of the metabolic flux Ics through the inter-membrane contact sites was revealed even at the highest magnitudes of calculated OMP for both cases of S = 30 V−1 (Fig. 5D) and S = 40 V−1 (Fig. 5E) in comparison to that obtained at S = 0 V−1 (Fig. 5F). On the other hand, MOM permeability to Pi− demonstrated highly pronounced dependence on generated OMP at both S = 30 V−1 (Fig. 5G) and S = 40 V−1 (Fig. 5H), in comparison to that obtained at S = 0 V−1 (Fig. 5I). A very sharp increase in the MOM permeability to Pi− at threshold levels of glucose was obtained at the voltage sensitivity parameter S = 40 V−1 (Fig. 5H), thus indicating the possibility of a significant and fast electrical modulation of the mitochondrial energy metabolism by generated OMP.
Discussion HKI is the major hexokinase isoform in the brain and it is mainly bound to mitochondria [4,6]. The binding site for HKI in brain mitochondria is VDAC [[5], [6], [7]], similarly as in the mitochondria of cancer cells, where VDAC is known to mainly bind HKII [7,49]. In cancer cells, generation of OMP, by considering the VDAC-HK complexes as a biological battery, was suggested to explain the control of the Warburg type metabolism and at least the short-time Crabtree effect as a result of an electrical suppression of the access to the mitochondrial ATP of all cytosolic consumers, except glycolysis [26,28,42,43]. On the other hand, the development of the Warburg type metabolism in the aged brain has been recently reported as a possible mechanism of enhanced cell death resistance, allowing survival of some neurons even in Alzheimer's disease [50,51].