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Constants for a Terrestrial Biotic Ligand Model (TBLM) to predict the Cu toxicity to barley root elongation (RE) were developed from controlled sand culture experiments. These constants were used to predict RE in soil culture. The competition of H + , Ca 2+ , and Mg 2+ to Cu 2+ toxicity were studied individually and independently, and linear relationships between EC50 free Cu 2+ and H + , Ca 2+ , and Mg 2+ activities were found, meaning that the cations H + , Ca 2+ , and Mg 2+ will alleviate the toxicity of Cu 2+ in solutions. Toxicity accompanying increasing concentration of solution ions other than Cu 2+ was observed and modeled as an osmotic effect which improved soil culture toxicity prediction. The Root Mean Square Error (RMSE) of %RE and EC50 (50% effective concentration) for soil toxicity prediction using TBLM parameters developed from sand culture are 13.0 and 0.23 respectively, which are as good as that of 14.0 and 0.24 using parameters that developed from soil culture itself. A model including the activity at the root plasma membrane surface was tested and found not to provide improvement over the use of bulk solution activity to predict metal toxicity. TBLM parameters obtained from water solution culture were unable to accurately predict the EC50s in soils whereas the parameters obtained from sand culture were able to predict the toxicity in soils. Including the toxicity of CuOH + was found to improve the toxicity prediction slightly. [ABSTRACT FROM AUTHOR]

Abstract: PorB class II from Neisseria meningitidis is a pore-forming, outer-membrane protein that can translocate to the host-cell membrane during Neisserial infections. This report describes development of tethered bilayer lipid membrane (tBLM) system to measure PorB conductance properties. The tBLM was fabricated by depositing a self-assembled monolayer of 1,2-dipalmitoyl-sn-glycero-3-phosphothioethanol (DPPTE) tethering lipid on a gold electrode and then using 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) liposomes to deposit the upper tBLM leaflet. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to monitor tBLM formation and subsequent PorB incorporation. The highly insulating tBLM exhibited a membrane resistance and capacitance of 2.5MΩcm2 and 0.7μF/cm2, respectively. PorB was incorporated into the tBLM in an active conformation, as evidenced by its mediation of ion passage and the decrease in membrane impedance. After PorB incorporation, the membrane resistance decreased to 0.6MΩcm2. As expected, the PorB channel was found to be non-selective, allowing the transport of both cations and anions. Cyclic voltammetry indicated that ferricyanide ions can also pass through the pores. The PorB-containing biomimetic interface developed in this study could potentially be used to screen for compounds that modulate PorB activity. [Copyright &y& Elsevier]

Alamethicin, a small transmembrane peptide, inserts into a tethered bilayer membrane (tBLM) to form ion channels, which we have investigated using electrical impedance spectroscopy. The number of channels formed is dependent on the incubation time, concentration of the alamethicin and the application of DC voltage. The properties of the ion channels when formed in tethered bilayers are similar to those for such channels assembled into black lipid membranes (BLMs). Furthermore, amiloride and certain analogs can inhibit the channel pores, formed in the tBLMs. The potency and concentration of the inhibitors can be determined by measuring the change of impedance. Our work illustrates the possibility of using a synthetic tBLM for the study of small peptide voltage dependent ion channels. A potential application of such a device is as a screening tool in drug discovery processes. [Copyright &y& Elsevier]