Closure of VDAC causes oxidative stress and accelerates the Ca-induced mitochondrial permeability transition in rat liver mitochondria

The electron transport chain of mitochondria is a major source of reactive oxygen species (ROS), which play a critical role in augmenting the Ca²⁺-induced mitochondrial permeability transition (MPT). Mitochondrial release of superoxide anions (O₂⁻) from the intermembrane space (IMS) to the cytosol is mediated by voltage dependent anion channels (VDAC) in the outer membrane. Here, we examined whether closure of VDAC increases intramitochondrial oxidative stress by blocking efflux of O₂⁻ from the IMS and sensitizing to the Ca²⁺-induced MPT. Treatment of isolated rat liver mitochondria with 5 μM G3139, an 18-mer phosphorothioate blocker of VDAC, accelerated onset of the MPT by 6.8 ± 1.4 min within a range of 100-250 μM Ca²⁺. G3139-mediated acceleration of the MPT was reversed by 20 μM butylated hydroxytoluene, a water soluble antioxidant. Pre-treatment of mitochondria with G3139 also increased accumulation of O₂⁻ in mitochondria, as monitored by dihydroethidium fluorescence, and permeabilization of the mitochondrial outer membrane with digitonin reversed the effect of G3139 on O₂⁻ accumulation. Mathematical modeling of generation and turnover of O₂⁻ within the IMS indicated that closure of VDAC produces a 1.55-fold increase in the steady-state level of mitochondrial O₂⁻. In conclusion, closure of VDAC appears to impede the efflux of superoxide anions from the IMS, resulting in an increased steady-state level of O₂⁻, which causes an internal oxidative stress and sensitizes mitochondria toward the Ca²⁺-induced MPT.     

Scaffolding protein Grb2-associated binder 1 sustains epidermal growth factor-induced mitogenic and survival signaling by multiple positive feedback loops

Grb2-associated binder 1 (GAB1) is a scaffold protein involved in numerous interactions that propagate signaling by growth factor and cytokine receptors. Here we explore in silico and validate in vivo the role of GAB1 in the control of mitogenic (Ras/MAPK) and survival (phosphatidylinositol 3-kinase (PI3K)/Akt) signaling stimulated by epidermal growth factor (EGF). We built a comprehensive mechanistic model that allows for reliable predictions of temporal patterns of cellular responses to EGF under diverse perturbations, including different EGF doses, GAB1 suppression, expression of mutant proteins, and pharmacological inhibitors. We show that the temporal dynamics of GAB1 tyrosine phosphorylation is significantly controlled by positive GAB1-PI3K feedback and negative MAPK-GAB1 feedback. Our experimental and computational results demonstrate that the essential function of GAB1 is to enhance PI3K/Akt activation and extend the duration of Ras/MAPK signaling. By amplifying positive interactions between survival and mitogenic pathways, GAB1 plays the critical role in cell proliferation and tumorigenesis.     

Formation of scale structure in lacustrine sock-eyed salmon <Emphasis Type="Italic">Oncorhynchus nerka</Emphasis> from water bodies of Kamchatka and determination of its age

The formation of the first annual zone in three populations of resident sock-eyed salmon—kokanee Oncorhynchus nerka of Kamchatka—has been studied. The length of fingerlings in mid-August did not reach 30 mm; in most analyzed juveniles, the remains of the yolk sac were present. In early September in lakes Tolmachevskoe and Kronotskoe, the length of the fingerlings was about 40 mm. The scales in fish from different populations begin to form in early September. Towards November, no more than nine sclerites are formed; a similar amount has been recorded at the beginning of summer also in fingerlings. When scales of adult fish are studied, there are 4 to 19 sclerites in the first annual zone. Apparently, the first annual ring does not form in a considerable portion of fingerlings.     

Age structure and growth of resident kokanee <Emphasis Type="Italic">Oncorhynchus nerka</Emphasis> of natural and introduced populations in lakes of Kamchatka

The analysis of growth of kokanee Oncorhynchus nerka demonstrated that there are differences in several indices between the natural population of Kronotskoe Lake and artificial populations of Tolmachevskoe and Klyuchevoe lakes. The highest specific rate of growth was recorded for individuals in Kronotskoe Lake; the lowest, in Tolmachevskoe and Klyuchevoe lakes (in 2006). For the Tolmachev kokanee, a multiyear tendency for a decrease in the gain of scales in generations was found, which is determined by the persisting formation of the population and the depletion of food resources. A considerable effect on the process of formation of the Tolmachev population of kokanee is made by commercial activity and the related transformation of the lake into a reservoir.     

Age-related characteristics of capsular angioarchitectonics of large human joints

Angioarchitectonics of 127 capsules of large joints in superior (brachial, ulnar, radiocarpal) and inferior (coxofemoral, genicular, talocrural) extremities have been studied using a complex of anatomical and histological techniques and morphometry. As demonstrate the investigations, in the fibrous and synovial membranes of the capsules in these joints, there are certain differences in the architectonics and in depth of the blood network arrangement. In accordance with the diameter of these vessels, density and character of distribution in the capsule membranes of the joints, it is possible to distinguish four circulatory networks. They have numerous anastomoses and form a united volumetric network of vessels. Certain general regularities are noted in the structure of the vascular networks of the capsule membrane in the extremity joints, as well as changes of their angioarchitectonics are revealed as adaptations to age morphofunctional changes in the connective tissue formations of the capsules.     

The regulation of L-type Ca2+ currents in cardiac myocytes of hibernating animals

The action of isoproterenol and BAY K 8644 on voltage-dependent Ca2+ currents in isolated ground squirrel cardiac myocytes was studied in two (active and hibernating) states of the animal. In cardiac myocytes of active animals the effect of both drugs was shown to depend on the holding potential. At Vh of about -50 mV both isoproterenol and BAY K 8644 increased the Ca2+ current and their action was additive. At Vh of about -20 mV, both drugs inhibited the Ca2+ current. In cardiac myocytes from hibernating animals, isoproterenol increased the Ca2+ current at any holding potentials, while the effect of BAY K 8644 did not differ significantly from its effect on active animals. The combined action of the two drugs caused the inhibition of the Ca2+ current at high holding potentials. In terms of the two-site Ca2+ channel model, this means that one of the two pathways of channel phosphorylation is blocked in hibernating animal cardiac cells, and BAY K 8644 restores this pathway.     

Parametric resonance and amplification of periodic disturbances in membranes containing ion channels with inactivation

Parametric resonance and amplification of periodic perturbations in the membrane transport of ions through channels with inactivation was studied in computational experiments. It has been shown that a periodic change in the membrane capacitance or in the applied electric current with a frequency approximately 2 omega 0 (omega 0--the own angular frequency of the membrane) may excite stable self-oscillations in the membrane with a frequency of approximately omega 0. For this to occur, the degree of the capacitance modulation m or the amplitude of the applied current i0 must exceed some critical values mcr and i0cr. Excitation of self-oscillations by alternating electric current of the frequency approximately 2 omega 0 has the characteristics of parametric resonance. This can be explained by the fact that the equivalent membrane inductance depends on ionic current and displays periodic changes with a frequency approximately 2 omega 0, as also does the current. Small-amplitude periodic changes in the capacitance (m less than mcr) with frequencies approximately 2 omega 0 may result in significant amplification of periodic perturbations with frequencies approximately omega 0.     

Parametric resonance and amplification in excitable membranes. The Hodgkin-Huxley model

It has previously been shown by different investigators that the excitable membrane shows a resonant sensitivity to periodic external perturbations, but its Q-factor is, as a rule, low. The present paper analyses the possible ways of increasing the membrane Q, using a model of the Hodgkin-Huxley type. It is found, in particular, that it can be increased considerably by modulating periodically the membrane capacitance or the activation and inactivation rate constants of ionic channels, with a frequency of about 2 fo (fo being the fundamental frequency of damped oscillations in the membrane), the extent of modulation not exceeding the critical value 2/Q. In this case, a significant parametric amplification of the membrane current takes place. If the modulation coefficient is above 2/Q, the membrane can display a parametric resonance that causes stable self-oscillations in the potential with a frequency approximately fo. The conditions for the realization of parametric amplification and resonance in biological membranes are discussed.