Effects of changes of intracellular pH on contraction in sheep cardiac Purkinje fibers

Intracellular pH (pHi) was measured with a pH-sensitive microelectrode in voltage-clamped sheep cardiac Purkinje fibers while tension was simultaneously measured. All solutions were nominally CO2/HCO3 free and were buffered with Tris. The addition of NH4Cl (5-20 mM) produced an initial intracellular alkalosis that was associated with an increase of twitch tension. At the same time, a component of voltage-dependent tonic tension developed. Prolonged exposure (greater than 5 min) to NH4Cl resulted in a slow recovery of pHi accompanied by a decrease of tension. Removal of NH4Cl produced a transient acidosis that was accompanied by a fall of force. In some experiments, there was then a transient recovery of force. If extracellular pH (pHo) was decreased, then pHi decreased slowly. Tension also fell slowly. An increase of pHo produced a corresponding increase of both force and pHi. The application of strophanthidin (10 microM) increased force and produced an intracellular acidosis. The addition of NH4Cl, to remove this acidosis partially, produced a significant increase of force. The above results show that contraction is sensitive to changes of intracellular but not extracellular pH. This pH dependence will therefore modify the contractile response to inotropic maneuvers that also affect pHi.     

Evolutionary conservation of the chromosomal configuration and regulation of amylase genes among eight species of the Drosophila melanogaster species subgroup

Nuclear DNA was extracted from each of the eight species comprising the Drosophila melanogaster species subgroup. Southern hybridization of this DNA by using a molecular probe specific for the alpha-amylase coding region showed that the duplicated structure of the amylase locus, first found in D. melanogaster, is conserved among all species of the melanogaster subgroup. Evidence is also presented for the concerted evolution of the duplicated genes within each species. In addition, it is shown that the glucose repression of amylase gene expression, which has been extensively studied in D. melanogaster, is not confined to this species but occurs in all eight members of the species subgroup. Thus, both the duplicated gene structure and the glucose repression of Drosophila amylase gene activity are stable over extended periods of evolutionary time.      

Effects of T-2 toxin and its congeners on membrane functions of cultured human fibroblasts

Cytotoxicity of T-2 toxin, HT-2 toxin, acetyl T-2, neosolaniol, and T-2 tetraol was compared between normal human fibroblasts and mutant I-cell human fibroblasts, which only produce 10 to 15% of lysosomal hydrolases present in normal fibroblasts. Both cleavage of 3-(4, 5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) and cell count by hemocytometer were used for evaluations. For all toxins, dose-related effects on both types of cultures were evident. Cytotoxicity of the above mycotoxins on both cell lines were similar, indicating that lysosomal enzymes were not involved in the toxicity of T-2 toxin and its congeners. An inhibitor of lysosomal cysteine proteases (E-64) did not alter the cytotoxicity of T-2 toxin. The decreasing order of toxicity was T-2 toxin, HT-2 toxin, neosolaniol, acetyl T-2 toxin, and T-2 tetraol in both cell lines. When normal human fibroblasts were loaded with the fluorescent dye Lucifer yellow CH (LY), a subsequent treatment of T-2 toxin did not disrupt lysosomal membranes. The uptake of LY was not affected by T-2 toxin, which indicated that T-2 toxin did not interfere with the endocytic pathway. Results indicate that T-2 toxin and its congeners do not exert their primary toxic effect through lysosomal enzymes, membranes, or via the endocytic pathway.     

Pheromone-mediated sexual selection in the mothUtetheisa ornatrix: Olfactory receptor neurons responsive to a male-produced pheromone

Male Utetheisa ornatrixhave a pair of eversible glandular brushes (coremata) which are displayed during precopulatory interactions with the female. Earlier studies have shown that a pheromone associated with the coremata, hydroxydanaidal (HD), is derived by the males from pyrrolizidine alkaloids (PAs) that they sequester as larvae from their foodplants (Crotalariaspp.) The PAs impart a distastefulness upon Utetheisathat protects both larvae and adults against predation. The receptor neurons specialized for detection of HD are housed in sensilla whose morphological features, as revealed by scanning electron microscopy, classify them as sensilla basiconica. The sensitivity and dynamic range of these receptor neurons were largely unaffected by whether the females were raised on an alkaloid-free diet or on a diet supplemented with Crotalariaseeds. Acetylation of the hydroxyl group of HD substantially reduced the activity of the molecule. None of the antennal sensilla examined contained receptor neurons sensitive to a PA (monocrotaline) or its N-oxide.     

Growth of Phytomonas serpens in a Defined Medium; Nutritional Requirements

ABSTRACT. Three strains of Phytomonas serpens two from tomatoes, Lycopersicon esculentum one from the insect Phtia picta (Hemiptera, Coreidae), were cultivated in a chemically defined medium developed from a defined medium for cultivating insect flagellates. Besides organic growth factors required by other insect trypanosomatids this flagellate requires, serine and inositol. Glutamine stimulates growth, and, surprisingly, does not require heme.     

Sequence variation in the outer-surface-protein genes of Borrelia burgdorferi

Borrelia burgdorferi is a spirochete pathogen transmitted among warm- blooded hosts by ixodid ticks. Frequency-dependent selection for variant outer-surface proteins might be expected to arise in this species, since rare variants are more likely to avoid immune surveillance in previously infected hosts. We sequenced the OspA and OspB genes of nine North American strains and compared them with nine strains previously described. For each gene, the mean number of synonymous substitutions per synonymous site and the mean number of nonsynonymous substitutions per nonsynonymous site show only a twofold excess of silent mutations. Synonymous rates vary widely along the OspB protein. Some regions show a significant excess of silent substitutions, while divergence in other regions is constrained by biased base composition or selection. The presence, in antigenically important regions of the protein, of significant variation among strains, as well as evidence for recombination among strains, should be considered in attempts to develop vaccines against this disease.      

Characterisation of a 34 kD protein from potato cyst nematodes, using monoclonal antibodies with potential for species diagnosis

Two monoclonal antibodies, which differentially recognise the two species of potato cyst nematodes (PCN), Globodera pallida and G. rostochiensis, are described. They have been shown to have potential for quantification of these two species, recognising proteins of the same molecular weight (34 kD) in both species. Further investigation showed these proteins to have isoelectric points at pH values of 5.7 in G. pallida and 5.9 in G. rostochiensis, in common with the proteins used by Fleming & Marks (1983) to differentiate the species of PCN. They are likely to be structurally very similar, with the same physiological function (and therefore similar concentrations) in the two species. In cross-reactivity tests with a wide range of soil nematode species, the antibodies reacted strongly only with species of the genus Globodera, and thereby confirmed their potential as the basis of a quantitative immunoassay likely to be useful in management of PCN populations.