Stress echocardiography: methods,indications and results

Stress echocardiography has become an important clinical tool to detect cardiac ischaemia and viability in addition to single photon emission tomography. Stress echocardiography has a high positive and negative predictive value, is less expensive than the nuclear methods and has no radiation exposure. It can easily be used in an emergency room and coronary care unit. Because of its feasibility, low cost and high diagnostic accuracy, it will become a very important technique in every hospital and will soon be a real alternative to the more time-consuming and expensive nuclear techniques. The current article gives a review of the methods of stress echocardiography.     

Cuticular hydrocarbons as potential mediators of cryptic species divergence in a mutualistic ant association

Upon advances in sequencing techniques, more and more morphologically identical organisms are identified as cryptic species. Often, mutualistic interactions are proposed as drivers of diversification. Species of the neotropical parabiotic ant association between Crematogaster levior and Camponotus femoratus are known for highly diverse cuticular hydrocarbon (CHC) profiles, which in insects serve as desiccation barrier but also as communication cues. In the present study, we investigated the association of the ants’ CHC profiles with genotypes and morphological traits, and discovered cryptic species pairs in both genera. To assess putative niche differentiation between the cryptic species, we conducted an environmental association study that included various climate variables, canopy cover, and mutualistic plant species. Although mostly sympatric, the two Camponotus species seem to prefer different climate niches. However in the two Crematogaster species, we could not detect any differences in niche preference. The strong differentiation in the CHC profiles may thus suggest a possible role during speciation itself either by inducing assortative mating or by reinforcing sexual selection after the speciation event. We did not detect any further niche differences in the environmental parameters tested. Thus, it remains open how the cryptic species avoid competitive exclusion, with scope for further investigations.     

Breath ethane as a marker of reactive oxygen species during manipulation of diet and oxygen tension in rats

Breath ethane, O₂consumption, and CO₂ productionwere analyzed in 24-mo-old female Fischer 344 rats that had been fedcontinuously ad libitum (AL) or restricted 30% of AL level (DR) dietssince 6 wk of age. Rats were placed in a glass chamber that was first flushed with air, then with a gas mixture containing 12%O₂. After equilibration, a sampleof the outflow was collected in gas sampling bags for subsequentanalyses of ethane and CO₂. TheO₂ andCO₂ levels were also directlymonitored in the outflow of the chamber. O₂ consumption andCO₂ production increased for DRrats. Hypoxia decreased O₂consumption and CO₂ production forthe AL-fed and DR rats. These changes reflect changes in metabolic ratedue to diet and PO₂. A significantdecrease in ethane generation was found in DR rats compared with AL-fedrats. Under normoxic conditions, breath ethane decreased from 2.20 to1.61 pmol ethane/ml CO₂. Duringhypoxia the levels of ethane generation increased, resulting in aDR-associated decrease in ethane from 2.60 to 1.90 pmol ethane/mlCO₂. These results support thehypothesis that DR reduces the level of oxidative stress.     

Methylation of DNA in developing embryos of the sea urchin Psammechinus miliaris

Embryos of the sea urchin Psammechinus miliaris have been labelled after fertilization with [6(-3)H]uridine and cultured in filtered sea water. 32-cell, blastula, gastrula and pluteus stages were harvested. The DNA from these embryos was purified and hydrolyzed and the nuclear bases were analyzed by means of high performance liquid chromatography. The ratios of 5-methylcytosine and cytosine demonstrate that the concentrations of 5-methylcytosine are essentially the same in the developmental stages examined (gamma = 95%), which contradicts the hypothesis that methylation of DNA plays a role in cell differentiation.     

Expression of the fragile site Xq27 in fibroblasts. I. Detection of Fra(X)(q27) in fibroblast clones from males with X-linked mental retardation

Summary Twelve fibroblast clones from two males with X-linked mental retardation expressed the fragile site Xq27 in 3%–38% of metaphases analyzed. The number of in vitro doublings during the cloning procedure had no evident influence on the induction of fragile X expression. The variability of fragile X expression seems to depend on cell properties acquired during culture rather than on properties originally inherent in the cells.     

Cloning of the mistletoe lectin gene and characterization of the recombinant A-chain.

Mistletoe lectin I (MLI) is the major active constituent of mistletoe extracts, which are widely used for adjuvant tumour therapy. The 66-kDa heterodimeric disulphide-linked glycoprotein is classified as type II ribosome-inactivating protein (RIP) due to the rRNA-cleaving enzyme activity of the A-subunit, also referred to as toxic entity. MLI and the close relative ricin both belong to the family of the two-chain plant type II RIP proteins. Isolation of the glycosylated proteins from plant material yield inhomogeneous material probably due to post-translational modifications. The aim of this study was to prepare pure and homogeneous protein as a prerequisite for structural and mechanistic studies in order to gain insight into the mode of action of this cytotoxic plant protein on tumour and immune cells. Of particular interest was to explain whether the differences in toxicity of ML and ricin are the result of variations of their enzymatic activities. By investigating the sequence homologies between the active sites of different RIPs we were able to deduce a set of primers which were suitable for specific amplification of the mistletoe lectin gene. Applying this PCR strategy the full-length 1923 nucleotide DNA sequence coding for the prepro-protein was obtained showing the existence of a single intron-free gene. In order to elucidate the molecular basis for the observed differences in cytotoxicity within the family of RIP the enzymatic A-subunit was expressed in a heterologous system. Expression of the A-chain in E. coli BL21/pT7 resulted in production of insoluble inclusion bodies constituting 20-30% of total protein. Refolding led to a pure and homogeneous protein species with an apparent molecular mass of 27 kDa and a pI value of 6.4. The ribosome-inactivating activity of the unglycosylated recombinant A-chain (IC50 20.5 pM) protein was in the same range as that of the glycosylated plant-derived ML A-chain (IC50 3.7 pM), which was very similar to that of ricin A-chain (IC50 4.9 pM). Thus, the higher cytotoxicity of ricin cannot be accountable for differences in the enzymatic activities of the type II RIP A-chains.