Quantum chemical calculation studies toward microscopic understanding of retention mechanism of Cs radioisotopes and other alkali metals in lichens.

We evaluate stability of cesium (Cs) and other alkali-metal cation complexes of lichen metabolites in both gas and aqueous phases to discuss why lichens can retain radioactive Cs in the thalli over several years. We focus on oxalic acid, (+)-usnic acid, atranorin, lecanoric acid, and protocetraric acid, which are common metabolite substances in various lichens including, e.g., Flavoparmelia caperata and Parmotrema tinctorum retaining Cs in Fukushima, Japan. By performing quantum chemical calculations, their gas-phase complexation energies and aqueous-solution complexation free energies with alkali-metal cations are computed for their neutral and deprotonated cases. Consequently, all the molecules are found to energetically favor cation complexations and the preference order is Li[Formula: see text]Na[Formula: see text]K[Formula: see text]Rb[Formula: see text]Cs[Formula: see text] for all conditions, indicating no specific Cs selectivity but strong binding with all alkali cations. Comparing complexation stabilities among these metabolites, lecanoric and protocetraric acids seen in medullary layer are found to keep higher affinity in their neutral case, while (+)-usnic acid and atranorin in upper cortex exhibit rather strong affinity only in deprotonated cases through forming stable six atoms' ring containing alkali cation chelated by two oxygens. These results suggest that the medullary layer can catch all alkali cations in a wide pH range around the physiological one, while the upper cortex can effectively block penetration of metal ions when the metal stress grows. Such insights highlight a physiological role of metabolites like blocking of metal-cation migrations into intracellular tissues, and explain long-term retention of alkali cations including Cs in lichens containing enough such metabolites to bind them.

Distribution and uptake of 137Cs in relation to alkali metals in a perhumid montane forest ecosystem.

We determined the content of radiocesium ((137)Cs) and alkali metals in soils, plants (2 ferns, a shrub and moss) and rainwater collected in an undisturbed forest ecosystem. The (137)Cs activity and the isotopic ratio of (137)Cs/Cs in the samples were used to interpret the distribution and uptake of (137)Cs and the alkali metals in plants. As a whole, the (137)Cs in plants was assimilated together with K but was not dependent on Cs. Different adaptations of fern species collected in ecological niches cause them to have different (137)Cs/Cs ratios. Diplopterygium glaucum is distributed at the edges of the forest; it usually has shallow organic layers, and the root takes up more stable Cs from mineral layers, leading to lower (137)Cs/Cs ratios than that in the understory Plagiogyria formosana and Rhododendron formosanum species. The steady supply of stable Cs through the uptake by D. glaucum from deep soils may gradually dilute the (137)Cs concentration and thus explain the lower (137)Cs/Cs ratio in the fern samples. The (137)Cs is predicted to be proportional to the Cs content across plant species in the biological cycle once isotopic equilibrium is attained.

Concentrations of major elements and mercury in unstimulated human saliva.

The aim of this study was a preliminary assessment of a possible role of human saliva in the diagnosis of some physiological and pathological changes in oral and body functions. Reliable procedures for collection and analysis of samples were established in order to assess total concentrations of Ca, K, Mg, Na, P, and Hg in whole unstimulated saliva. Possible relationships between element concentrations and sex, age, smoking, illness conditions, or side effects resulting from the use of drugs were investigated. The effects of stimulated or unstimulated collection procedures, dental prosthesis, and amalgam fillings were also evaluated. Total concentrations of major cations and Hg in whole saliva from 33 healthy adults living in the Siena district showed a coefficient of variation ranging from 11% (P) to 53% (Na) and average values were in the same range of those previously reported for unstimulated saliva. Healthy males had significantly higher concentrations of K, Na, P, and Na/K, Na/Ca, Na/Mg, and Na/P values than females. Age, smoking, dental prosthesis, and amalgam fillings had no significant effects on the concentrations of major elements. On the contrary, concentrations of Hg were positively correlated to the number of amalgam fillings and increased at a rate of about 1.9 microg/L for each filling. No correlations were found between Hg concentrations and those of major elements. Comparisons with literature data showed a different composition (particularly for Na and Hg concentrations) between unstimulated and stimulated saliva. Samples from patients affected by idiopathic pulmonary fibrosis had significantly higher concentrations of K and the maximum value was measured in a patient affected by acute pulmonary edema. This increase was likely the result of pharmacological treatments with tricyclic antidepressants and/or saline solutions. Data reported in this study, although preliminary, contribute to the assessment of levels of major cations (some of them very little investigated) and Hg in whole unstimulated human saliva and provides consistent support for further research on the possible use of this easy accessible matrix as a diagnostic tool of body function changes.

Differential regulation of tight junction permeability during development of the retinal pigment epithelium.

The retinal pigment epithelium (RPE) is an epithelial region of the blood-brain barrier. During embryogenesis, permeability of the barrier gradually decreases. A culture model of RPE development revealed differences in how tight junctions regulate the paracellular diffusion of ionic and nonionic solutes (Ban Y and Rizzolo LJ. Mol Vis 3: 18, 1997). To examine these differences, the permeation of ionic and nonionic monosaccharides was compared with mannitol, and the permeation of the alkali metals was compared with sodium. The order of permeation was 3-O-methlyglucose = glucosamine = mannitol > N-acetylneuraminic acid. The ratio of N-acetylneuraminic acid to mannitol permeability decreased with embryonic age of the RPE or exposure to retinal-conditioned medium. Neither the ratio nor the permeability was affected by inhibiting transcytosis. The ratio increased if tight junctions were disrupted in low-calcium medium. The permeation of cations followed the sequence cesium > rubidium > potassium = sodium > lithium and was unaffected by embryonic age or retinal-conditioned medium. These results are considered in terms of a model in which the size distribution, charge, or number of open junctional pores could be modulated. It suggests that different subpopulations of pores can be regulated independently during development.

The response induced by intracellular cyclic AMP in isolated olfactory receptor cells of the newt.

1. Responses induced by intracellular cyclic nucleotides were analysed in isolated olfactory receptor cells of the newt under a voltage-clamp condition by using the patch pipette in a whole-cell recording configuration. Cyclic nucleotides were applied by diffusion from the patch pipette. 2. Introduction of either cyclic AMP or cyclic GMP caused a transient inward current in cells held at -50 mV. The response amplitude was dose-dependent with the Hill coefficient of 3 and half-saturating concentration of 300 microM (concentration in the pipette) for both cyclic AMP and cyclic GMP. Cyclic CMP was less effective than those two nucleotides. 3. The response to intracellular cyclic AMP was seen in all cilia-bearing cells, but not in cells which lost the cilia during dissociation. The response latency was shorter when cyclic AMP was introduced into the ciliated terminal swelling (ca 0.2 s) rather than into the cell body (ca 1.4 s). These results suggest that the sensitivity to intracellular cyclic AMP is confined to the cilia. 4. The cyclic AMP-induced current was transient (half decay time, ca 2.3s) despite the fact that cyclic AMP was continuously loaded from the patch pipette. The response time course was controlled by Ca2+; the reduction of external Ca2+ concentration (replaced with Mg2+) or loading the cell with 50 mM-EGTA prolonged the cyclic AMP-induced responses. The Ca2(+)-induced suppression was reversible. 5. The reversal potential of the cyclic AMP-induced transient current was -4.8 +/- 3.8 mV, and that of the current re-induced by Ca2+ removal was 1.5 +/- 2.1 mV, suggesting that both currents flowed through the same ionic channel. The channel permeates all alkali metal ions with the permeability ratios of PLi:PNa:PK:PRb:PCs = 0.93:1:0.93:0.91:0.72, but not Cl- or choline ions. 6. These results demonstrate that the cyclic AMP-induced response and the odorant-induced response of the isolated olfactory cell have nearly identical characteristics. The present study supports the notion that cyclic AMP is the internal messenger mediating olfactory transduction.