Anesthetic effects on pulmonary allergic responses in rats: changes in sensitivity to serotonin.

Subsequent to observations that pulmonary responses to antigen challenge are of different magnitudes in sensitized rats that are anesthetized with different drugs, we conducted studies to test whether the alterations in responses were due to changes in airway responsiveness to cholinergic or serotonergic challenge, opioid-receptor mediated events, or changes in mast cell mediator release. Immunoglobulin E-sensitized rats anesthetized with ketamine/urethan had larger changes in lung resistance and plasma histamine after pulmonary antigen challenge compared with rats anesthetized with fentanyl-droperidol. Blockade of opioid receptors with naloxone did not affect the responses. In unsensitized rats, airway responses to aerosolized methacholine were similar for the two anesthetics, indicating unchanged smooth muscle responsiveness; however, airway responses to intravenous serotonin were enhanced by ketamine and ablated by droperidol. We conclude that ketamine- and droperidol-induced alterations of pulmonary allergic responses are due to changes in sensitivity to serotonin and in mast cell mediator release. We speculate that mast cell mediator release may be modulated by a serotonin receptor-linked mechanism.     

Changes in gas exchange characteristics and water use efficiency of mangroves in response to salinity and vapour pressure deficit

Summary Measurements were made of the photosynthetic gas exchange properties and water use efficiency of 19 species of mangrove in 9 estuaries with different salinity and climatic regimes in north eastern Australia and Papua New Guinea. Stomatal conductance and CO₂ assimilation rates differed significantly between species at the same locality, with the salt-secreting species, Avicennia marina, consistently having the highest CO₂ assimilation rates and stomatal conductances. Proportional changes in stomatal conductance and CO₂ assimilation rate resulted in constant and similar intercellular CO₂ concentrations for leaves exposed to photon flux densities above 800 mol·m^-2·s^-1 in all species at a particular locality. In consequence, all species at the same locality had similar water use efficiencies. There were, however, significant differences in gas exchange properties between different localities. Stomatal conductance and CO₂ assimilation rate both decreased with increasing salinity and with increasing leaf to air vapour pressure deficit (VPD). Furthermore, the slope of the relationship between assimilation rate and stomatal conductance increased, while intercellular CO₂ concentration decreased, with increasing salinity and with decreasing ambient relative humidity. It is concluded from these results that the water use efficiency of mangroves increases with increasing environmental stress, in this case aridity, thereby maximising photosynthetic carbon fixation while minimising water loss.Contribution No. 459 from the Australian Institute of Marine Science     

Greater sensitivity to vanadate of rat renal relative to cardiac (Na++K+)-ATPase

Vanadate (VO₄^?3) produces a positive inotropic effect in rats and also promotes diuresis as well as natriuresis. Although the mechanism(s) of these effects is uncertain, in the kidney, VO₄^?3 may act through inhibition of (Na⁺+K⁺)-ATPase activity, whereas in the heart, other or additional mechanisms are likely. Under the assay conditions used in the present study, microsomal (Na⁺+K⁺)-ATPase activities from rat kidney cortex and medulla were inhibited to a greater extent than was left ventricular (Na⁺+K⁺)-ATPase activity over a range of VO₄^?3 concentrations. The apparent dissociation constant for left ventricular (Na⁺+K⁺)-ATPase (10.95 ± 1.26 × 10^?7M VO₄^?3) was significantly greater than that of (Na⁺+K⁺)-ATPase from the cortex (3.46±0.96×10^?7 M VO₄^?3) or the medulla (3.32±0.7×10^?7M VO₄^?3, N=6, P<.05) whereas there were no significant differences between the effects of VO₄^?3 on (Na⁺+K⁺)-ATPase from the cortex and medulla. The greater inhibition by VO₄, of (Na⁺+K⁺)-ATPase from the cortex relative to that of the left ventricle, occurred over a range of Na⁺ and K⁺ concentrations, and K⁺ enhanced the inhibition by VO₄^?3 to a greater extent for (Na⁺+K⁺)-ATPase from the cortex than the left ventricle. These results suggest that renal (Na⁺+K⁺)-ATPase is more sensitive than left ventricular (Na⁺+K⁺)-ATPase to inhibition by VO₄^?3 and would, therefore, be more likely to be modulated $\text{in}$$\text{vivo.}$     

Phylogeny of Greya (Lepidoptera: Prodoxidae), based on nucleotide sequence variation in mitochondrial cytochrome oxidase I and II: congruence with morphological data

The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from nucleotide sequence variation across a 765-bp region in the cytochrome oxidase I and II genes of the mitochondrial genome. Most parsimonious relationships of 25 haplotypes from 16 Greya species and two outgroup genera (Tetragma and Prodoxus) showed substantial congruence with the species relationships indicated by morphological variation. Differences between mitochondrial and morphological trees were found primarily in the positions of two species, G. variabilis and G. pectinifera, and in the branching order of the three major species groups in the genus. Conflicts between the data sets were examined by comparing levels of homoplasy in characters supporting alternative hypotheses. The phylogeny of Greya species suggests that host-plant association at the family level and larval feeding mode are conservative characters. Transition/transversion ratios estimated by reconstruction of nucleotide substitutions on the phylogeny had a range of 2.0-9.3, when different subsets of the phylogeny were used. The decline of this ratio with the increase in maximum sequence divergence among taxa indicates that transitions are masked by transversions along deeper internodes or long branches of the phylogeny. Among transitions, substitutions of A-->G and T-->C outnumbered their reciprocal substitutions by 2-6 times, presumably because of the approximately 4:1 (77%) A+T-bias in nucleotide base composition. Of all transversions, 73%-80% were A<-->T substitutions, 85% of which occurred at third positions of codons; these estimates did not decrease with an increase in maximum sequence divergence of taxa included in the analysis. The high frequency of A<-->T substitutions is either a reflection or an explanation of the 92% A+T bias at third codon positions.      

Digestion of haemoglobin by schistosomes: 35 years on

Adult schistosomes obtain nutrients by digesting haemoglobin, which they obtain from ingested host red blood cells. Here John Dalton, Angela Smith, Karen Clough and Paul Brindley argue that a cathepsin L proteinase recently identified in their laboratory as the predominant cysteine proteinase activity of Schistosoma mansoni may play the leading role in haemoglobin digestion. They discuss the importance of elucidating the roles of both cathepsin B and cathepsin L in the digestion of haemoglobin, since both should be considered important targets to which novel schistosomicidal agents could be directed.