DIFFERENCES IN SUSCEPTIBILITY TO INSECTICIDES BETWEEN ADULTS AND LARVAE OF HOUSEFLY, MUSCA DOMESTICA (L.)

Abstract  In this paper, we reported the differences in susceptibility to insecticides between adults and larvae of housefly, Musca domestica (L.), and the mechanisms for the differences. The larvae of housefly were much more tolerant to insecticides than the adults, and the tolerance ratio to cyhalothrin was as high as 205.5 for susceptible strain. Mechanism studies showed that higher GST activity was associated with higher insecticide tolerance in the larvae. The co-toxicity coefficient of the mixture of cyhalothrin and methylene dithiocyanate(4:1) on pyrehid-resistant houseflies was 188.     

Kinetics of pyrophosphate induced iron release from diferric ovotransferrin

The kinetics of pyrophosphate-induced iron release from diferric ovotransferrin were studied spectrophotometrically at 37 degrees C in 0.1 M HEPES, pH 7.0. At high pyrophosphate concentrations, the kinetics are biphasic, indicating that the rates of iron release from the two, presumably noninteracting iron-binding sites of ovotransferrin are different. The pseudo-first-order rate constants for iron release from both the fast and slow sites exhibit a hyperbolic dependence on pyrophosphate concentrations. The data suggest that pyrophosphate forms complexes with the two iron-binding sites of ovotransferrin prior to iron removal. The stability constants of the complex formed with the fast site (Keqf) and slow site (Keqs) are 8.3 M-1 and 40.4 M-1, respectively. The first-order rate constants for the dissociation of ferric-pyrophosphate from the fast site (k2f) and the slow site (k2s) are 0.062 and 0.0044 min-1, respectively. Results from urea gel electrophoresis studies suggest that iron is released at a much faster rate from the N-terminal binding site of ovotransferrin. At high pyrophosphate concentration, only C-monoferric-ovotransferrin is detected during the course of iron release. At low pyrophosphate concentration, however, a detectable amount of N-monoferric-ovotransferrin is accumulated. This result is consistent with the kinetic finding that the site with a higher k2 (0.062 min-1) has a lower affinity toward pyrophosphate (Keq = 8.3 M-1) whereas the site with a lower k2 (0.0044 min-1) has a higher affinity for pyrophosphate (Keq = 40.4 M-1).     

Length, mass, and denaturation of double-stranded RNA molecules compared with DNA

The contour lengths of linear, double-stranded (ds) RNAs from mycovirus PcV and Pseudomonas bacteriophage ø6 have been measured with samples prepared for the electron microscope from 0.05 to 0.5 M NH₄Cl solutions. A linear dependence of contour length on the logarithm of ionic strength was found and compared with that of dsDNA (pBR322, linearized and open-circular forms). Conditions for molecular weight determinations of any natural dsRNA by electron microscopy have been established, and the method has been calibrated with ø6 dsRNA of known nucleotide sequence. The results imply that dsRNA in 0.20 M NH₄Cl solution has a rise per basepair of 0.271 nm, which is shorter than that in the A-conformation (4%) and in the A′-conformation (10%). The thermal behavior of dsRNA in terms of melting temperature and exhibition of fine structure of melting curves was found to be generally similar to that of dsDNA, as expected from the literature. Folding of dsRNA in ethanolic solution was similar to that of dsDNA. However, in contrast to dsDNA, coiled coils could not be induced by ethanol, which is consistent with dsRNA being stiffer than dsDNA. Concerning dsDNA, the results show that a contraction in rise per basepair by 0.1 nm is coupled with an increase in the winding angle between basepairs by 0.47°, as qualitatively predicted by polyelectrolyte theory.     

The effects of pentobarbital, fentanyl-droperidol, ketamine-xylazine and ketamine-diazepam on core and surface body temperature regulation in adult male rats

Many commonly used anesthetics cause hypothermia by inhibiting central and peripheral thermoregulatory mechanisms. Although it is probable that a loss of thermal homeostasis contributes directly to the high mortality frequently reported following anesthesia of laboratory rodents, this adverse effect has been investigated rarely in the past. This study compared the effects of three parenteral anesthetics (pentobarbital, ketamine-xylazine and ketamine-diazepam) and a neuroleptanalgesic (fentanyl-droperidol) on core and surface body temperature regulation in rats. Results showed a profound hypothermia with all dosages of pentobarbital, while ketamine-xylazine and ketamine-diazepam caused a dose-dependent depression in core and surface body temperature. All dosages of fentanyl-droperidol (Innovar-Vet) caused minimal depression in thermoregulation, suggesting that it is the drug which requires the least external thermal support. Results of this study also suggested that inability to compensate for heat loss, particularly from the body core, may profoundly influence anesthetic toxicity and the safety of anesthetic procedures.     

The effects of pentobarbital, fentanyl-droperidol, ketamine-xylazine and ketamine-diazepam on arterial blood pH, blood gases, mean arterial blood pressure and heart rate in adult male rats

Although anesthetics are known to cause respiratory and cardiovascular depression in humans, these adverse effects rarely have been investigated in laboratory rodents. This study evaluated the effects of four different injectable drugs, pentobarbital, fentanyl-droperidol (Innovar-Vet), ketamine-xylazine and ketamine-diazepam on the respiratory and cardiovascular systems of rats. Results showed marked acidosis, hypercarbia and hypoxia with high doses of Innovar-Vet, moderate respiratory depression with all dosages of pentobarbital and minimal respiratory depression with ketamine-xylazine and ketamine-diazepam. Innovar-Vet, ketamine-xylazine and pentobarbital caused profound hypotension, particularly at high dosages, while ketamine-diazepam caused the least depression in mean arterial blood pressure of all drugs evaluated. None of the drugs studied produced significant alterations in heart rate. Throughout all dosages investigated, the ketamine-diazepam combination showed the least overall effects on ventilation and perfusion of the four parenteral drug combinations studied.     

Structural basis for altered soybean agglutinin lectin binding between a murine metastatic lymphoma and an adhesive low malignant variant

By selection for plastic adhesiveness we have previously established a variant tumor line (ESb-MP) from the metastatic murine lymphoma ESb. In contrast to the parental line, the adhesion variant is significantly decreased in malignancy and is altered in the capacity to bind soybean agglutinin (SBA) lectin. Here we show biochemically that the major SBA-binding cell-surface component of ESb-MP cells is the T200 glycoprotein. In ESb cells, T200 antigens bind SBA only after sialidase treatment. Enzymatic studies suggested that glycans detected by the lectin with or without sialidase treatment are different. Inhibition of N-glycosylation by tunicamycin and biosynthetic labeling revealed two T200 chains for ESb-MP cells that were larger in size than the single chain detected in ESb cells. Studies on the biosynthesis revealed that ESb-MP cells expressed two precursor chains for T200 whereas ESb cells displayed only one. There was no size difference detectable in the mature T200 molecules of ESb and ESb-MP cells. Our data suggest that the molecules differ in expression of O-linked glycans that can be recognized by SBA. Additional O-linked sugars on ESb-MP T200 molecules seem to be expressed in particular after trimming of the second T200 precursor chain.     

Characterization of the specific pyruvate transport system in Escherichia coli K-12.

A mutant of Escherichia coli K-12 lacking pyruvate dehydrogenase and phosphoenolpyruvate synthase was used to study the transport of pyruvate by whole cells. Uptake of pyruvate was maximal in mid-log phase cells, with a Michaelis constant for transport of 20 microM. Pretreatment of the cells with respiratory chain poisons or uncouplers, except for arsenate, inhibited transport up to 95%. Lactate and alanine were competitive inhibitors, but at nonphysiological concentrations. The synthetic analogs 3-bromopyruvate and pyruvic acid methyl ester inhibited competitively. The uptake of pyruvate was also characterized in membrane vesicles from wild-type E. coli K-12. Transport required an artificial electron donor system, phenazine methosulfate and sodium ascorbate. Pyruvate was concentrated in vesicles 7- to 10-fold over the external concentration, with a Michaelis constant of 15 microM. Energy poisons, except arsenate, inhibited the transport of pyruvate. Synthetic analogs such as 3-bromopyruvate were competitive inhibitors of transport. Lactate initially appeared to be a competitive inhibitor of pyruvate transport in vesicles, but this was a result of oxidation of lactate to pyruvate. The results indicate that uptake of pyruvate in E. coli is via a specific active transport system.     

Tolerance induction in mice by conjugates of monoclonal immunoglobulins and monomethoxypolyethylene glycol. Transfer of tolerance by T cells and by T cell extracts

The specific tolerance induced in mice by conjugates of human monoclonal IgG (HIgG) with monomethoxypolyethylene glycol (mPEG) was transferred to normal mice by spleen cells or a surface immunoglobulin negative (sIg-) Lyt-2+ subpopulation of these cells. Although transferable tolerance was demonstrable 6 to 14 days after treatment of the cell donors with tolerogen, the state of tolerance persisted in the treated mice for at least 43 days. Moreover, an extract prepared by freezing and thawing of the sIg- spleen cells obtained from mice 6 days after treatment with HIgG(mPEG)20 was capable of reducing (greater than 85%) the immune response of normal mice to heat aggregated HIgG. On the basis of these results, it is suggested that similar tolerogenic mPEG derivatives of xenogeneic monoclonal immunoglobulins (XIg) may prove to be useful therapeutic agents in man when administered before treatment with the unmodified XIg.