Estimating the number of genetic elements that defer senescence inDrosophila

Summary Although many different physiological and biochemical changes characterize the process of senescence, little is understood of the genetic elements that determine its age of onset. We provide here the first estimates of the number of genetic factors that extend longevity inDrosophila melanogaster. Life span was measured in F₁, F₂ and backcrosses of true-breeding long and short-lived stocks ofD. melanogaster, established by selection. Estimates of the number of effective factors delaying senescence range from about 0.3 to 1.5, indicating control by a single factor. The distribution of longevity shows this to arise as selection acts on the short-lived parental stock. Life span is extended at the cost of early fecundity.     

Effects of acute pleural effusion on respiratory system mechanics in dogs

We determined regional (Vr) and overall lung volumes in six head-up anesthetized dogs before and after the stepwise introduction of saline into the right pleural space. Functional residual capacity (FRC), as determined by He dilution, and total lung capacity (TLC) decreased by one-third and chest wall volume increased by two-thirds the saline volume added. Pressure-volume curves showed an apparent increase in lung elastic recoil and a decrease in chest wall elastic recoil with added saline, but the validity of esophageal pressure measurements in these head-up dogs is questionable. Vr was determined from the positions of intraparenchymal markers. Lower lobe TLC and FRC decreased with added saline. The decrease in upper lobe volume was less than that of lower lobe volume at FRC and was minimal at TLC. Saline increased the normal Vr gradient at FRC and created a gradient at TLC. During deflation from TLC to FRC before saline was added, the decrease in lung volume was accompanied by a shape change of the lung, with greatest distortion in the transverse (ribs to mediastinum) direction. After saline additions, deflation was associated with deformation of the lung in the cephalocaudal and transverse directions. The deformation with saline may be a result of upward displacement of the lungs into a smaller cross-sectional area of the thoracic cavity.     

On the mechanisms of ATP-induced and succinate-induced redistribution of cations in isolated rat liver cells

1. The ability of external ATP to induce calcium uptake in isolated rat liver cells was further characterized. Stimulation of calcium uptake was specific for ATP, other nucleotides or ATP metabolites had no comparable effect. ATP was dephosphorylated while stimulating calcium uptake, but there was no stoichiometry between ATP hydrolysis and calcium uptake nor did dephosphorylation depend on calcium concentration. ATP acted from outside and was dephosphorylated by an ecto-ATPase of the cells. 2. In addition to its direct action, ATP enhanced succinate-dependent calcium uptake in a cooperative fashion. This is best explained by different sites of action. ATP increases cell membrane permeability while succinate stimulates uptake into mitochondria. 3. ATP was able to lower Na+ and K+ gradients and the pH gradient between cells and incubation medium. Increasing calcium concentration counteracted this effect though calcium uptake was then stimulated. 4. Succinate alone did not affect monovalent cation gradients but raised the pH gradient. It partially counteracted the ATP effects on these gradients. 5. Since catecholamine-like actions of ATP may be mediated by an increase in cytoplasmic calcium concentration, the action of extracellular ATP can be taken as a model to study the role of calcium as a transmitter of hormone actions. From interdependence between ATP-stimulated and succinate-stimulated calcium uptake, conclusions can be drawn on the resulting cytoplasmic calcium concentration and its effect on plasma membrane permeability.     

Heterogeneity of leukotriene receptors in guinea-pig trachea

The selective leukotriene (LT) antagonist FPL 55712 antagonized the contractile activity of synthetic LTD4 and E4 on guinea-pig trachea. Schild analysis of the antagonism provided evidence for two distinct receptors for LTD4: one with significantly higher affinity for FPL 55712 than the other. LTE4 appears to interact preferentially with the high affinity receptor.     

Synthesis of Desthiobiotin from 7,8-Diaminopel-argonic Acid in Biotin Auxotrophs of Escherichia coli K-12

The synthesis of desthiobiotin from 7,8-diaminopelargonic acid (DAP) was demonstrated in resting cell suspensions of Escherichia coli K-12 bioA mutants under conditions in which the biotin locus was derepressed. The biosynthetically formed desthiobiotin was identified by chromatography, electrophoresis, and by its ability to support the growth of yeast and those E. coli biotin auxotrophs that are blocked earlier in the biotin pathway. Optimal conditions for desthiobiotin synthesis were determined. Desthiobiotin synthetase activity was repressed 67% when partially derepressed resting cells were incubated in the presence of 3 ng of biotin per ml. Serine, bicarbonate, and glucose stimulated desthiobiotin synthesis apparently by acting as sources of CO(2). The results of this study are consistent with an earlier postulated pathway for biotin biosynthesis in E. coli: pimelic acid --> 7-oxo-8-aminopelargonic acid --> DAP --> desthiobiotin --> biotin.     

Virus with a Multipartite Superhelical DNA Genome from the Ichneumonid Parasitoid Campoletis sonorensis

Virus was isolated from the lumen of the calyx region of ovaries in the parasitoid wasp Campoletis sonorensis (Hymenoptera: Ichneumonidae), and the nature of the viral DNA was analyzed. DNA purified from a homogeneous band of virus contained double-stranded superhelical molecules which were polydisperse in molecular weight. At least 25 different covalently closed circles were present, ranging in molecular weight from 4.0 x 10(6) to 13.6 x 10(6). The virus DNA was analyzed with restriction enzymes, and the nature of the genetic complexity was evaluated by Southern blot hybridization of native superhelical and relaxed circular virus DNA and of SalI- and HindIII-digested DNA. The data suggest that most of the variously sized covalently closed DNAs were composed primarily of nonhomologous sequences. The different size classes of covalently closed viral DNAs did not appear to exist in equimolar concentrations. However, there was no evidence from observation of virus particles in the electron microscope or from virus fractionation experiments that a mixture of viruses was present in the calyx fluid. The results from this study suggest' that the virus isolated from C. sonorensis, like those isolated from other endoparasitic hymenoptera, may belong to a new class of DNA viruses in which the genome is multipartite, with each DNA existing as a superhelical molecule.     

Contraction of isolated airway smooth muscle by synthetic leukotrienes C4 and D4

The pharmacology of leukotrienes (LT) C4 and D4 in isolated airway smooth muscle was investigated. In rat trachea, neither LTC4 or D4 elicited a response. In contrast, LTC4 was a potent contractile agonist in guinea-pig trachea, bronchus and parenchymal lung strip. Similar effects were obtained with LTD4 in trachea and parenchyma. In trachea and bronchus, the concentration-response curve to LTC4 was biphasic: indomethacin converted the biphasic response curve to a simple sigmoidal shape and enhanced the maximum contractile response. The SRS-A antagonist FPL 55712 antagonized the effect of LTD4 in both trachea and parenchyma. As regards LTC4-induced contraction of trachea and bronchus, FPL 55712, depending on concentration, either antagonized, or antagonized and enhanced the maximum contractile response. The enhancement of the maximum contractile response by FPL 55712 was not apparent when indomethacin was present. FPL 55712 failed to antagonize the effect of LTC4 in parenchyma.     

A DNA-unwinding enzyme induced in bacteriophage-T4-infected Escherichia coli cells.

A single-stranded DNA-dependent ATP gamma-phosphohydrolase of Mr 56000 induced after infection of Escherichia coli cells with bacteriophage T4, probably the ATPase dependent on gene dda of the phage, was isolated. Studies on the enzyme show that in the presence of ATP and M2+ ions it is capable of dissociating partially double-stranded fd bacteriophage DNA into the single strands and that some 3000 enzyme copies are required to unwind the 6400-nucleotides-long DNA. Unwinding is inhibited by reducing the length of the single-stranded portion of DNA to two nucleotides. In addition it can be inhibited by sulfhydryl reagents which block the ATPase or by trapping free enzyme molecules in the assay system. The results suggest that unwinding is initiated near the single-stranded portion of the DNA and is driven by the ATPase. It further appears that the enzyme unwinds by adsorbing to the DNA. Affinity of the enzyme for double-standed DNA is not detectable by DNA binding assay.     

Mutagenic effect on L5178Y mouse lymphoma cells by growth in ethylene oxide-sterilized polycarbonate flasks

Summary The mutation frequency of L5178Y mouse lymphoma cells to resistance to 5′-bromo-2′-deoxyuridine increased 6-to 14-fold after growth in ethylene oxide-sterilized polycarbonate culture flasks compared to growth in glass flasks. No comparable increase was observed when L5178Y cells were growth in identical polycarbonate culture flasks sterilized by autoclaving.