The micronuclei frequencies in the buccal cell epithelium of young people of different age and gender in Ukraine

The results of study of micronuclei (MN) frequencies among the participants of Ukrainian school biological olympiads are presented. Totally 266 persons have been inspected. The distribution of MN frequencies correspond to the Poisson's distribution with lambda = 2.5. The average frequency of micronuclei in males was 2.4 +/- 0.15%, in females it was 2.7 +/- 0.14%. The difference of the average MN frequencies for these two groups was statistically insignificant. The individual micronuclei frequencies varied from 0 to 8.3%, the average MN frequency in the general group was 2.5 +/- 0.11%, (limits 2-5%). The micronuclei frequencies in different age groups of males and females were compared. Significantly higher MN frequencies in females than in males at the age of sixteen were detected. The age-related changes of micronuclei frequencies (14-18 age) were different for females compared to males.     

The charge state of an ion channel controls neutral polymer entry into its pore

Electrostatic potentials created by fixed or induced charges regulate many cellular phenomena including the rate of ion transport through proteinaceous ion channels. Nanometer-scale pores of these channels also play a critical role in the transport of charged and neutral macromolecules. We demonstrate here that, surprisingly, changing the charge state of a channel markedly alters the ability of nonelectrolyte polymers to enter the channel's pore. Specifically, we show that the partitioning of differently-sized linear nonelectrolyte polymers of ethylene glycol into the Staphylococcus aureus α-hemolysin channel is altered by the solution pH. Protonating some of the channel side chains decreases the characteristic polymer size (molecular weight) that can enter the pore by ∼25% but increases the ionic current by ∼15%. Thus, the “steric” and “electric” size of the channel change in opposite directions. The results suggest that effects due to polymer and channel hydration are crucial for polymer transport through such pores. Received: 16 March 1997 / Accepted: 24 April 1997     

Blockage of Anthrax PA63 Pore by a Multicharged High-Affinity Toxin Inhibitor

Single channels of Bacillus anthracis protective antigen, PA₆₃, were reconstituted into planar lipid membranes and their inhibition by cationic aminopropylthio-β-cyclodextrin, AmPrβCD, was studied. The design of the highly efficient inhibitor, the sevenfold symmetrical cyclodextrin molecule chemically modified to add seven positive charges, was guided by the symmetry and predominantly negative charge of the PA₆₃ pore. The protective action of this compound has been demonstrated earlier at both single-molecule and whole-organism levels. In this study, using noise analysis, statistics of time-resolved single-channel closure events, and multichannel measurements, we find that AmPrβCD action is bimodal. The inhibitor, when added to the cis side of the membrane, blocks the channel reversibly. At high salt concentrations, the AmPrβCD blockage of the channel is well described as a two-state Markov process, in which both the on- and off-rates are functions of the salt concentration, whereas the applied voltage affects only the off-rate. At salt concentrations smaller than 1.5 M, the second mode of AmPrβCD action on the channel is discovered: addition of the inhibitor enhances voltage gating, making the closed states of the channel more favorable. The effect depends on the lipid composition of the membrane.     

Correlative Interrelations between the Oxygen Consumption Rate, Body Temperature and Activities of the Key Antioxidant Enzymes of Liver of Mus musculus

Using one-, two-, and three-dimensional statistical methods, there were analyzed peculiarities of distribution and the degree of the correlative-regressional dependence between the parameters characterizing the oxygen consumption rate (V _O2), body temperature (BT), activities of three key enzymes of the antioxidant system - superoxide dismutase (SOD), catalase (CL), and glutathion peroxidase (GP) in 15 females of the laboratory population of Mus musculus. The performed studies have shown that the three-dimensional non-linear models better correspond to the actual data and clearly demonstrate specificity of the antioxidant enzymes, as regulatory targets. Changes of the SOD and CL activities depend mainly on V _O2, whereas GP can be the target equally accessible for the regulatory factors of oxidative processes and thermoregulation.     

Tubulin-blocked state of VDAC studied by polymer and ATP partitioning

Recently reported functional interaction between voltage-dependent anion channel of the outer mitochondrial membrane, VDAC, and dimeric tubulin is observed as a reversible channel blockage. Using partitioning of poly-(ethylene glycol)s of different molecular weights and reversal potential measurements, we probe the size and ion selectivity of the fully open and tubulin-blocked states of VDAC reconstituted into planar lipid bilayers. While the effective radius of the channel decreases by only a factor of 1.34±0.15, the selectivity reverses from initially anionic to cationic. Directly measuring ATP partitioning we demonstrate that these changes prohibit ATP from entering the channel in its tubulin-blocked state.     

Docking of a single phage lambda to its membrane receptor maltoporin as a time-resolved event

We have been able to observe the first step in bacteriophage infection, the docking of phage lambda to its membrane receptor maltoporin, at the single-particle level. High-resolution conductance recording from a single trimeric maltoporin channel reconstituted into a planar lipid bilayer has allowed detection of the simultaneous and irreversible interaction of the phage tail with all three monomers of the receptor. The formation of a phage-maltoporin complex affects the channel transport properties. Our analysis demonstrates that phage attaches symmetrically to all three receptor monomers. The statistics of sugar binding to the phage-receptor complex on the side opposite to phage docking show that the monomers of maltoporin still bind sugar independently, with the kinetic constants expected from those of the phage-free receptor. This finding suggests that phage docking does not distort the structure of the receptor, and that the phage-binding regions are close to, but do not overlap with, the sugar-binding domains of the maltoporin monomers. However, ion fluxes through the pores of maltoporin in the phage-receptor complex share a new common pathway. We expect that the present study contributes to the current needs for structural information on the functional complexes involved in intercellular recognition.     

Persister-promoting bacterial toxin TisB produces anion-selective pores in planar lipid bilayers

We studied membrane activity of the bacterial peptide TisB involved in persister cell formation. TisB and its analogs form multi-state ion-conductive pores in planar lipid bilayers with all states displaying similar anionic selectivity. TisB analogs differing by ±1 elementary charges show corresponding changes in selectivity. Probing TisB pores with poly-(ethylene glycol)s reveals only restricted partitioning even for the smallest polymers, suggesting that the pores are characterized by a relatively small diameter. These findings allow us to suggest that TisB forms clusters of narrow pores that are essential for its mechanism of action.     

VDAC regulation: role of cytosolic proteins and mitochondrial lipids

It was recently asserted that the voltage-dependent anion channel (VDAC) serves as a global regulator, or governor, of mitochondrial function (Lemasters and Holmuhamedov, Biochim Biophys Acta 1762:181–190, 2006). Indeed, VDAC, positioned on the interface between mitochondria and the cytosol (Colombini, Mol Cell Biochem 256:107–115, 2004), is at the control point of mitochondria life and death. This large channel plays the role of a “switch” that defines in which direction mitochondria will go: to normal respiration or to suppression of mitochondria metabolism that leads to apoptosis and cell death. As the most abundant protein in the mitochondrial outer membrane (MOM), VDAC is known to be responsible for ATP/ADP exchange and for the fluxes of other metabolites across MOM. It controls them by switching between the open and “closed” states that are virtually impermeable to ATP and ADP. This control has dual importance: in maintaining normal mitochondria respiration and in triggering apoptosis when cytochrome c and other apoptogenic factors are released from the intermembrane space into the cytosol. Emerging evidence indicates that VDAC closure promotes apoptotic signals without direct involvement of VDAC in the permeability transition pore or hypothetical Bax-containing cytochrome c permeable pores. VDAC gating has been studied extensively for the last 30 years on reconstituted VDAC channels. In this review we focus exclusively on physiologically relevant regulators of VDAC gating such as endogenous cytosolic proteins and mitochondrial lipids. Closure of VDAC induced by such dissimilar cytosolic proteins as pro-apoptotic tBid and dimeric tubulin is compared to show that the involved mechanisms are rather distinct. While tBid mostly modulates VDAC voltage gating, tubulin blocks the channel with the efficiency of blockage controlled by voltage. We also discuss how characteristic mitochondrial lipids, phospatidylethanolamine and cardiolipin, could regulate VDAC gating. Overall, we demonstrate that VDAC gating is not just an observation made under artificial conditions of channel reconstitution but is a major mechanism of MOM permeability control.