Current-voltage relationships of a sodium-sensitive potassium channel in the tonoplast ofChara corallina

Summary The membrane of mechanically prepared vesicles ofChara corallina has been investigated by patch-clamp techniques. This membrane consists of tonoplast as demonstrated by the measurement of ATP-driven currents directed into the vesicles as well as by the ATP-dependent accumulation of neutral red. Addition of 1mm ATP to the bath medium induced a membrane current of about 3.2 mA·m^–2 creating a voltage across the tonoplast of about –7 mV (cytoplasmic side negative). On excised tonoplast patches, currents through single K⁺-selective channels have been investigated under various ionic conditions. The open-channel currents saturate at large voltage displacements from the equilibrium voltage for K⁺ with limiting currents of about +15 and –30 pA, respectively, as measured in symmetric 250mm KCl solutions. The channel is virtually impermeable to Na⁺ and Cl^–. However, addition of Na⁺ decreases the K⁺ currents. TheI–V relationships of the open channel as measured at various K⁺ concentrations with or without Na⁺ added are described by a 6-state model, the 12 parameters of which are determined to fit the experimental data.     

Transfusion induces blood donor-specific suppressor cells

Transfusion with blood from the organ donor before transplantation can prolong the survival of renal allografts in the rat. To determine if the beneficial effect of preoperative blood transfusion was due to the generation of donor-specific suppressor cells, in vivo and in vitro adoptive transfer experiments were performed. Lymphoid cells were harvested from transfused and untreated rats. These cells were then either (1) transferred to lightly irradiated (200 R) syngeneic hosts which were subsequently challenged with a kidney allograft (in vivo assay) or (2) titrated as regulator cells into naive unidirectional MLC such that the regulator and responder populations were syngeneic. In the LEW-RT1 to DA-RT1av1 strain combination, the adoptive transfer of thoracic duct lymph (TDL) or lymph node (LN) cells (5 x 10(7) to 7.5 x 10(7) cells) from DA animals transfused with LEW blood, 7 days previously into syngeneic (DA), lightly irradiated (200 R) hosts resulted in the indefinite survival of LEW kidney allografts. The phenomenon was blood donor-specific and dose-dependent. In contrast the adoptive transfer of spleen cells (10(7) to 10(8] from blood transfused hosts 7 days after transfusion had no effect on renal allograft survival. In vitro the addition of LN or TDL regulator cells, harvested from DA rats transfused with LEW blood, to a unidirectional MLC (DA responders, LEW stimulators) resulted in a significant depression of the proliferative response when compared with the proliferation of these same cells without the addition of these regulator cells or with the addition of LN or TDL regulator cells from a DA rat transfused with third party (PVG-RT1c) blood. The depression of the proliferative response observed in vitro, was blood donor specific. When LN or TDL regulator cells from a DA rat transfused with PVG-RT1c blood were added to a unidirectional MLC between DA responders and PVG stimulators, a significant depression in the proliferative response was observed. These in vitro findings were confirmed in two other strain combinations (LEW-PVG, and DA-PVG). Thus a single blood transfusion results in the induction of donor-specific suppressor cells detectable both in vivo and in vitro 7 days after transfusion in some but not all lymphoid compartments.     

Immobilization of enzymes with polyaziridines.

A novel method of enzyme immobilization using a low molecular weight prepolymer of tri-functional aziridines which can immobilize enzymes both by covalent attachment and entrapment within a gel matrix is described. The enzymes are immobilized on a solid support and exhibit an excellent retention of enzymatic activity. The immobilization procedure is essentially a single step process which can be easily performed at room temperature or 4 degrees C in either aqueous solution or in an inert organic solvent. The polyaziridines used in the immobilization are nontoxic, available in bulk at low cost and completely miscible with water and many organic solvents, thus providing one of the most satisfactory methods of immobilization available.     

Very fast purification of ornithine decarboxylase with high yield from mouse kidney and generation of a monoclonal antibody

Based on methods for ornithine-decarboxylase purification published previously we developed an improved procedure for purification of the enzyme from the kidneys of testosterone-treated NMRI mice. Advantages of the new procedure are, that inactivation of the enzyme during purification is largely reduced by fast methods for purification and by the use of proteinase inhibitors. That way we got pure ornithine decarboxylase within 60 h with a yield of about 70%. A part of the highly purified ornithine decarboxylase was used for the generation of monoclonal antibodies.     

A sensitive and rapid luminescence sandwich assay for antibodies to hepatitis-B surface antigen (Anti-HBsAg)

A chemiluminescent assay for hepatitis-B surface antigen is described which used an isoluminol derivative as the label. The assay is precise intra-assay CV, 1.96-2.45%; inter-assay CV, 5.26-8.11% and has a lower detection limit for hepatitis-B surface antigen of 1.3U/I.     

Measures of geographic range size: the effects of sample size

A number of methods have been used for quantifying the sizes of the geographic ranges of species. The consequences of different levels of sampling (the proportion of actual spatial occurrences) are explored for eight of these, using data on the occurrences of butterfly species on a 10 × 10 km grid across Britain. For all methods, the percentage error of estimation (PEE) decreases with the number of 10 × 10 km squares which a species occupies, most rapidly for extent measures, and more rapidly for area measures than for measures of numbers of units occupied. The rate of decline in PEE itself falls as sampling effort increases. At a given sampling level, rank correlations between range sizes measured by different methods are generally high, but there is no consistent change in the magnitude of these correlations as the level of sampling increases. The composition of the set of species with the smallest range sizes changes with the level of sampling.     

15N2 measurement of nitrogen fixation by legumes and actinorhizals: theory and practice

A gas-tight chamber has been constructed to calibrate the ¹⁵N isotope dilution method against direct ¹⁵N₂ measurements. The theoretical basis for such estimates is given, and the practical problems associated with the experiments are discussed.