Phloretin-Induced Reduction in Dipole Potential of Sterol-Containing Bilayers

The phloretin-induced reduction in the dipole potential of planar lipid bilayers containing cholesterol, ergosterol, stigmasterol, 7-dehydrocholesterol and 5α-androstan-3β-ol was investigated. It is shown that effects depend on the type and concentration of membrane sterol. It is supposed that the effectiveness of phloretin in reducing the dipole potential of the bilayers that contain cholesterol, ergosterol and 7-dehydrocholesterol correlates with the ordering and condensing effects. The role of the concentration-dependent ability of different sterols to promote lateral heterogeneity in membranes is also discussed.     

Asymmetry of syringomycin E channel studied by polymer partitioning

To probe the size of the ion channel formed by Pseudomonas syringae lipodepsipeptide syringomycin E, we use the partial blockage of ion current by penetrating poly(ethylene glycol)s. Earlier experiments with symmetric application of these polymers yielded a radius estimate of approximately 1 nm. Now, motivated by the asymmetric non-ohmic current-voltage curves reported for this channel, we explore its structural asymmetry. We gauge this asymmetry by studying the channel conductance after one-sided addition of differently sized poly(ethylene glycol)s. We find that small polymers added to the cis-side of the membrane (the side of lipodepsipeptide addition) reduce channel conductance much less than do the same polymers added to the trans-side. We interpret our results to suggest that the water-filled pore of the channel is conical with cis- and trans-radii differing by a factor of 2-3 and that the smaller cis-radius is in the 0.25-0.35 nm range. In symmetric, two-sided addition, polymers entering the pore from the larger opening dominate blockage.     

Effect of inhibitors of synthesis of dopamine and its antagonists on Hydra attenuata regeneration

Obvious inhibition of the hydra regeneration with no subsequent morphological abnormalities, was shown to occur when using alpha-methylthyrosine and 3 Jthyrosine. alpha-Methyldopa induced a slight inhibition but a considerable morphological change: ectopic tentacles, projections, bipolar forms in the gastric fragment. The apical and basal fragments did not suffer. The role of neurotransmitters in the hydra morphogenesis is discussed.     

Tooth replacement rates in early chondrichthyans: a qualitative approach

The continuous replacement of teeth throughout their lifetime is a common characteristic of most chondrichthyans. This process was already present in the earliest representatives of the group. It has been well established that different species of extant sharks show rapid tooth replacement rates; however, some authors have suggested that in early chondrichthyans this rate might have been much slower. Here we present a qualitative approach to analyse tooth replacement rates in the Early Devonian shark Leonodus carlsi , the earliest tooth-bearing shark known to date. For this, we have examined 1,103 isolated teeth from Celtiberia, Spain. Our study provides strong evidences of an extremely slow dental replacement in this primitive chondrichthyan based on three independents analyses: (1) statistical analysis of the wear degree, demonstrating that teeth remain functional for a long period of time; (2) analysis of both the histological and the morphological features of the teeth cusps suggests that this chondrichthyan used a maturation process that optimizes its function, thus worn teeth show an efficient working shape that implies their teeth remained functional for a long time after being modelled by use; and (3) estimations of size increments between teeth (Δs) of the same dental family for some recent sharks whose rates of replacement were known prove that Δs is inversely proportional to the rate of replacement ( R ² = 0.8327). The estimated values of tooth replacement rates obtained from Δs for L. carlsi and for some Late Devonian cladoselachian sharks are significatively slower than those observed in current sharks.     

Ligands of boron in Pisum sativum nodules are involved in regulation of oxygen concentration and rhizobial infection

Boron (B) is an essential nutrient for N₂‐fixing legume–rhizobia symbioses, and the capacity of borate ions to bind and stabilize biomolecules is the basis of any B function. We used a borate‐binding‐specific resin and immunostaining techniques to identify B ligands important for the development of Pisum sativum–Rhizobium leguminosarum 3841 symbiotic nodules. arabinogalactan–extensin (AGPE), recognized by MAC 265 antibody, appeared heavily bound to the resin in extracts derived from B‐sufficient, but not from B‐deficient nodules. MAC 265 stained the infection threads and the extracellular matrix of cortical cells involved in the oxygen diffusion barrier. In B‐deprived nodules, immunolocalization of MAC 265 antigens was significantly reduced. Leghaemoglobin (Lb) concentration largely decreased in B‐deficient nodules. The absence of MAC 203 antigens in B‐deficient nodules suggests a high internal oxygen concentration, as this antibody detects an epitope on the lipopolysaccharide (LPS) of bacteroids typically expressed in micro‐aerobically grown R. leguminosarum 3841. However, B‐deprived nodules did not accumulate oxidized lipids and proteins, and revealed a decrease in the activity of the major antioxidant enzyme ascorbate peroxidase (APX). Therefore, B deficiency reduced the stability of nodule macromolecules important for rhizobial infection, and for regulation of oxygen concentration, resulting in non‐functional nodules, but did not appear to induce oxidative damage in low‐B nodules.     

Prevalence of hyperthyroidism after exposure during childhood or adolescence to radioiodines from the chornobyl nuclear accident: dose-response results from the Ukrainian-American Cohort Study

Relatively few data are available on the prevalence of hyperthyroidism (TSH concentrations of <0.3 mIU/liter, with normal or elevated concentrations of free T4) in individuals exposed to radioiodines at low levels. The accident at the Chornobyl (Chernobyl) nuclear plant in Ukraine on April 26, 1986 exposed large numbers of residents to radioactive fallout, principally to iodine-131 ((131)I) (mean and median doses = 0.6 Gy and 0.2 Gy). We investigated the relationship between (131)I and prevalent hyperthyroidism among 11,853 individuals exposed as children or adolescents in Ukraine who underwent an in-depth, standardized thyroid gland screening examination 12-14 years later. Radioactivity measurements taken shortly after the accident were available for all subjects and were used to estimate individual thyroid doses. We identified 76 cases of hyperthyroidism (11 overt, 65 subclinical). Using logistic regression, we tested a variety of continuous risk models and conducted categorical analyses for all subjects combined and for females (53 cases, n = 5,767) and males (23 cases, n = 6,086) separately but found no convincing evidence of a dose-response relationship between (131)I and hyperthyroidism. There was some suggestion of elevated risk among females in an analysis based on a dichotomous dose model with a threshold of 0.5 Gy chosen empirically (OR = 1.86, P = 0.06), but the statistical significance level was reduced (P = 0.13) in a formal analysis with an estimated threshold. In summary, after a thorough exploration of the data, we found no statistically significant dose-response relationship between individual (131)I thyroid doses and prevalent hyperthyroidism.     

Long-term exposure of Boeckellagibbosa (Copepoda, Calanoida) to in situ levels of solar UVB radiation

1. The freshwater calanoid copepod Boeckella gibbosa is typical of high elevation lakes and ponds in Patagonia (Argentina). Previous studies have shown that this species is highly tolerant to short-term exposure to natural and artificial UVB radiation, and that its tolerance is due to photoreactivation by longer wavelength radiation. In this study, we investigate the potential sublethal effects of solar radiation after prolonged exposure.
2. We incubated B. gibbosa at 1 m depth in oligotrophic Lake Toncek for 24 days. The incubation chambers were 1.2 l acrylic cylinders covered with appropriate filters in order to obtain three radiation treatments: visible radiation only, visible radiation + UVA and visible radiation + UVA + UVB.
3. The three treatments did not differ significantly in variables considered as indicators of survival (number of individuals), reproduction (proportion of ovigerous females, clutch size) and development (instar composition). Although resistance to solar UVB radiation is certainly a requisite to live in transparent high elevation habitats, the fact of being effectively exposed to natural levels of UVB radiation does not seem to have measurable consequences on an already adapted species, such as B. gibbosa     

Transport of large organic ions through syringomycin channels in membranes containing dipole modifiers

The effect of the membrane dipole potential (φ _d ) on conductance and the steady-state number of functioning channels formed by cyclic lipodepsipeptide syringomycin E (SRE) in bilayer lipid membranes made from phosphocholine and bathed in 0.4 M solution of sodium salts of aspartate, gluconate, and chloride was shown. The φ _d value varied with the introduction of phloretin to membrane bathing solutions, which reduces φ _d and RH 421, which increases φ _d . It was established that, in all studied systems, an increase in the membrane dipole potential caused a decrease in the steady-state number of open channels. In systems containing sodium salts of aspartate (Asp) or gluconate (Glc), changes in the number of functioning channels are one order lower than those of systems that contain sodium chloride. At the same time, the conductance (g) of single SRE channels in the membranes bathed in NaCl solution increases with increase in φ _d and in the systems containing NaAsp or NaGlc the conductance of single channels does not depend on the φ _d . The latter is due to the lack of cation/anion selectivity of the SRE channels in these systems. The different channel-forming activity of SRE in the experimental systems is determined by the gating charge of the channel and the partition coefficient of the dipole modifiers between the lipid and aqueous phases.     

The search for proteins with immunochemical affinity to plant stress proteins at cold-adapted endemic Baikal fishes

The search for proteins with immunochemical affinity to plant stress proteins in endemic Baikal fishes shows the presence of proteins, immunochemically related to plant heat-stabile proteins and plant uncoupling protein CSP 310. Western blotting showed that among the native cytoplasmic proteins of endemic Baikal fishes there are proteins immunochemically related to heat-stabile plant proteins with molecular weights about 480, 200-290, 150, 140 and about 90-100kD. SDS-electrophoresis showed the presence of polypeptides with molecular weights 23, 17 and 14kD in all species investigated and an additional 35kD polypeptide in Cottocomephorus grewingki. The search for polypeptides with immunochemical affinity to plant stress uncoupling protein CSP 310 in endemic Baikal fishes shows the presence of a 14kD polypeptide, immunochemically related to it.