Thorotrast uptake and transit in embryonic glia, heart fibroblasts and neurons in vitro

Thorotrast (colloidal ThO₂) is incorporated into coated vesicles, various agranular vesicles and sacs, and a surface-associated system of membranous channels in times as short as 1 min by single cultured glial and heart cells. Thorotrast appears in ‘C’-shaped bodies and in small, dense bodies of the lysosomal series within ca. 25 min. With longer chase periods, thorotrast ‘clears’ from all cytoplasmic organelles except the lysosomal series. The technique of applying thorotrast and using varying chase periods fails to distinguish a class of membranous organelles, located close to the cell periphery, that might serve as a source of new cell surface during locomotory activity. Similarly, thorotrast (colloidal ThO₂) is incorporated into almost all classes of membrane-bounded organelles of growth cones and axons of single nerve cells in vitro in times as short as 1 min. This includes elements of the smooth endoplasmic reticulum. No thorotrast enters the lysosomal granules in this short time. During various chase periods, the tracer disappears from the initial sites of incorporation and accumulates in dense bodies of the lysosome series within growth cones and axons. ‘C’-shaped bodies may be an intermediate in that process. No unique sites of endocytotic activity or of a complete absence of endocytosis were observed that could be correlated with growth cone function and axonal elongation, though the presence of the tracer in agranular sacs of the smooth endoplasmic reticulum in growth cones could reflect hypothesized cycling of cell surface (Bray, 1973).     

A comparison of wild-type and mutant ribitol dehydrogenases from Klebsiella aerogenes

A ribitol dehydrogenase (ribitol-NAD(+) oxidoreductase, EC. 1.1.1.56) having increased specificity and catalytic efficiency toward xylitol was isolated from mutant strains of Klebsiella aerogenes, which were selected for increased growth rate on xylitol over the ribitol dehydrogenase constitutive wild-type organism. 2. The mutant enzyme was purified to homogeneity and its general characteristics were compared with those of the previously purified wild-type enzyme. 3. Initial-velocity steady-state kinetic parameters were determined for both wild-type and mutant enzymes and the results compared. 4. The results are interpreted in terms of a model in which the mutant enzyme results from a small change of amino acid sequence, which affects both the stability and conformational equilibria of the molecule.     

The chromosomes and linkage groups ofPisum

By appropriate genetical studies using reciprocal translocation stocks it has been possible to confirmLamprecht's evidence that inPisum there are seven linkage groups. Lamm's evidence for six linkage groups has been shown to be due to incomplete knowledge of the chromosomal structure of certain interchange lines.It is suggested thatLamprecht's system of chromosomal nomenclature should be universally adopted forPisum.Lamm &Miravelle's extended tester set has been accordingly renumbered and the intercrossing of the interchange lines completed in order to extend the confirmatory evidence as to their chromosomal constitution.     

The Effects of Direct Instillations of a Therapeutic Mixture Into the Tracheobronchial Tree

Twenty-two patients with chronic productive bronchitis or bronchiectasis were treated by direct instillations of normal saline and N-acetylcysteine into the trachea through a percutaneous catheter following a period of conventional routine therapy.The instillation, using either normal saline or varying concentrations of N-acetylcysteine did not produce significant change in alveolar gas exchange as reflected by measurement of arterial PaCO₂ and the alveolar arterial gradient for oxygen during and after the introduction of the medication into the bronchial tree. Studies were carried out after patients had been stabilized breathing pure oxygen on an IPPB machine for 30 minutes.Evaluation of the treatment by means of pulmonary function tests demonstrated significant improvement in overall function following therapy.The results indicate that the technique of tracheobronchial lavage is physiologically benign and that overall improvement in pulmonary function can be obtained by this means in cases of the type described in this study.     

Factors affecting the use of chloramphenicol acetyltransferase as a marker for Brassica genetic transformation

The CAT gene which codes for the enzyme chloramphenicol acetyltransferase was found to be ineffective as a reporter gene in cells and tissues of Brassica species. High levels of endogenous CAT activity were found to be widespread among this genus and did not appear to be distributed in a tissue- or cell-specific manner. Moreover, the presence of an inhibitor of CAT activity was discovered in Brassica napus and Brassica juncea. This inhibitor appeared to act selectively on bacterial CAT in transgenic plants. These findings provided an explanation for difficulties experienced in the detection of transgenic CAT activity in B. napus.     

Social competition among gynes in halictine bees: The influence of bee size and pheromones on behavior

Solitary gynes of two species of social bees, Lasioglossum (Evylaeus) malachurumand L. (E.) pauxillum(Hymenoptera: Halictidae), were observed in the field and in the laboratory during the solitary (spring) phase of their life cycles. Fighting over nests among gynes of the former species is common when nests are being provisioned and can result in serious injury or even death to one or both interactants. The payoff is occasional acquisition of a nest. In contrast, fighting was never observed in the field among gynes of L. pauxillum.Several factors determine the outcome of such fights in L. malachuram,these include relative sizes of the two opponents as well as nest ownership. Dyadic interactions in the laboratory reveal that size influences the behavioral strategies of the gynes of both species, with the larger of two individuals in a dyadic interaction being on average more aggressive. Furthermore, in a second experimental series with L. malachurum,application to the smaller gyne of synthetically derived macrocyclic lactones found in the species' Dufour's gland pheromone mixture significantly decreased the aggressive tendencies of the larger such that its behavior was no longer significantly different from that for the smaller gyne. Therefore, among gynes, aggressive pheromonal signaling, coupled with other possible signal modalities, is probably an integral part in the communication system.     

Cl− channels in basolateral renal medullary memnbranes: III. Determinants of single-channel activity

Summary We evaluated the effects of vawrying aqueous Cl^– concentrations, and of the arginyl- and lysyl-specific reagent phenylglyoxal (PGO), on the properties of Cl^– channels fused from basolaterally enriched renal medullary vesicles into planar lipid bilayers. The major channel properties studied were the anion selectivity sequence, anionic requirements for, channel activity. and the efects of varying Cl^– concentrations and/or PGO on the relation between holding voltageV _H -mV) and open-time probability (P _o).Reducingcis Cl^– concentrations, in the range 50–320mm, produced a linear reduction in fractional open time (P _v) with a half-maximal reduction inP _o atcis Cl^–170mM. Channel activity was sustained by equimolar replacement ofcis Cl^– with F^–, but not with impermeant isethionate. Fortrans solutions, the relation between Cl^– concentration andP ₀ at 10mm Cl^–. Reducingcis Cl^– had no effect on the gating charge (Z) for channel opening, but altered significantly the voltage-independent, energy (G) for channel opening.Phenylglyoxal (PGO) reducedZ and altered G for Cl^– channel activity when added tocis, but nottrans solutions, Furthermore, in the presence ofcis PGO, reducing thecis Cl^– concentration had no effect onZ but altered G. Thus we propose thatcis PGO and,cis Cl^– concentrations affect separate sites determining channel activity at the extracellular faces of, these Cl^– channels.