The relationship between water velocity,energetic costs,and microhabitat use in four North American stream fishes

Freshwater crayfish are key members of aquatic communities due to their large size and abundance. Although most commonly regarded as herbivores and detritivores, they are also selective predators. The crayfish plague fungus Aphanomyces astaci (Schikora) led to the elimination of a stock of white-clawed crayfish, Austropotamobius pallipes (Lereboullet) from Lough Lene, Co. Westmeath, in 1987. Samples taken of the flora and benthic communities of two Irish lakes, one (Lough Bane) formerly containing crayfish and the other (Lough Lene) immediately following a plague outbreak, were compared to similar samples taken a year later and ecological shifts were noted and compared to laboratory feeding results. Over time, Chara strands increased in mean length, and molluscs became more abundant.     

Primary sequence and functional expression of a novel ouabain-resistant Na,K-ATPase. The beta subunit modulates potassium activation of the Na,K-pump.

In order to understand the molecular mechanism of ouabain resistance in the toad Bufo marinus, Na,K-ATPase alpha and beta subunits have been cloned and their functional properties tested in the Xenopus laevis oocyte expression system. According to sequence comparison between species, alpha 1, beta 1, and beta 3 isoforms were identified in a clonal toad urinary bladder cell line (TBM 18-23). The sequence of the alpha 1 isoform is characterized by two positively charged amino acids (Arg, Lys) at the N-terminal border of the H1-H2 extracellular loop and no charged amino acid at the C terminus, a pattern distinct from the ouabain-resistant rat alpha 1 isoform. The coexpression of alpha 1 beta 1 or alpha 1 beta 3 TBM subunits in the Xenopus oocyte resulted in the expression of identical maximum Na,K-pump currents with identical inhibition constant for ouabain (Ki) (alpha 1 beta 1: 53 +/- 3 microM; n = 7 vs. alpha 1 beta 3: 57 +/- 3.0 microM; n = 8) but distinct potassium half activation constant (K1/2) (alpha 1 beta 1: 0.87 +/- 0.08 mM, n = 16; alpha 1 beta 3: 1.29 +/- 0.07 mM, n = 17; p less than 0.005). We conclude that (i) the TBM alpha 1 isoform is necessary and sufficient to confer the ouabain resistant phenotype; (ii) the beta 3 or beta 1 subunit can associate with the alpha 1 equally well without affecting the ouabain-resistant phenotype; (iii) some specific sequence of the beta subunit can modulate the activation of the Na,K-pump by extracellular potassium ions.     

The P2 element of the td intron is dispensable despite its normal role in splicing.

The P2 region of group I introns has been proposed to be involved in the correct positioning of the P1 5'-splice site duplex in the catalytic core (Michel, F., and Westhof, E. (1990) J. Mol. Biol. 216, 585-610). The behavior of delta P2 deletion mutants of the td intron is consistent with this hypothesis. The delta P2 mutants are capable of site-specific hydrolysis, indicating that the conformation of the ribozyme is not grossly altered, but they are incapable of transesterification reactions at the splice sites, as would be predicted if P1 is not appropriately aligned within the catalytic core. Nevertheless, the function of the P2 element can be bypassed in specific pseudorevertants isolated by genetic selection from the delta P2 mutants. These results, together with phylogenetic data, support the existence of alternate strategies to create a functional P1-core interaction.     

TAP1 mutant mice are deficient in antigen presentation, surface class I molecules, and CD4-8+ T cells.

The transporter associated with the antigen processing 1 (TAP1) gene encodes a subunit for a transporter, presumed to be involved in the delivery of peptides across the endoplasmic reticulum membrane to class I molecules. We have generated mice with a disrupted TAP1 gene using embryonic stem cell technology. TAP1-deficient mice are defective in the stable assembly and intracellular transport of class I molecules and consequently show severely reduced levels of surface class I molecules. These properties are strikingly similar to those described for the TAP2 mutant cell line RMA-S. Cells from the TAP1-deficient mice are unable to present cytosolic antigens to class I-restricted cytotoxic T cells. As predicted from the near absence of class I surface expression, TAP1-deficient mice lack CD4-8+ T cells.     

Quality assurance in pathology. Cytologic and histologic correlation.

In this study we used a computerized program to compare the cytologic and histologic diagnoses made in a three-year period with the aim of evaluating the data obtained as an index of the diagnostic accuracy of cytology in a pathology quality assurance program. Concordance between the cytologic and histologic diagnoses was observed in 83.2% of the cases. In 1.2% the cytologic diagnosis was suspected malignancy, and 78.4% of these cases were positive for tumor at histologic examination. Analysis of the data must be performed in accordance with the anatomic site involved, and discordance must be investigated by a pathologist, especially in view of the different modalities of cytologic and histologic sampling. Analytic data on the breast, bladder and lung are presented.     

Electrical impedance of white spruce shoots in relation to pressure-volume analysis and free sugar content

Electrical impedance measurements made on white spruce, Picea glauca (Moench) Voss, stems were related to shoot free sugar contents and to osmotic, turgor and water potential. During seasonal dormancy induction, there were commensurate increases in free sugar contents, osmotic potential at full turgor and impedance which resulted in linear relationships among these variables. When measured over the course of laboratory drying, impedance increased curvilinearly with decreasing relative water content. There was a linear increase in impedance with decreasing water potential, with a break point coincident with the turgor loss point, possibly attributed to disruption to current flow through broken plasmodesmatal connections between adjacent cells. This technique offers a non-destructive method to measure tissue free sugar content, and therefore, short- and long-term shifts in parameters historically derived from pressure-volume analysis.     

Rewarming of feet by lower and upper body exercise

The capacity of different types of exercise to rewarm the body, especially the feet, was studied. Six healthy male subjects wearing winter clothing (2.4 clo, 0.37 degrees C.m2.W-1) were exposed on three occasions to -15 degrees C for 120 min. For the first 60 min the subjects were cooled while sitting motionless and for the latter 60 min they were submitted to cycle ergometer exercise (CE), arm ergometer exercise (AE) or step exercise (ST). The rate of work in CE (about 350 W) served as a reference value for AE and ST. The cooling resulted in an average 1.7 (SEM 0.03) degrees C decrease in mean body temperature (Tb) corresponding to a 425 (SEM 9) kJ heat debt. The ST increased most effectively mean skin, rectal and lower body skin temperatures as well as dry heat loss. The ST increased Tb by 0.83 (SEM 0.16) degrees C, CE by 0.10 (SEM 0.11) degrees C and AE by only 0.07 (SEM 0.12) degrees C. At the end of the exercise the foot temperature was approximately 6 degrees C higher in ST than in CE. The superior rewarming by ST was apparently due to its low mechanical efficiency. Because the increase in Tb could not explain all the changes in foot temperatures, increased circulation and metabolism of the feet would also appear to have been involved.     

pH track of expanding bacterial populations

A method of pH distribution measurements in agar nutrient media containing expanding bacterial populations is described. It is based on measuring pH microsamples taken at different points of the media. The sample volume was 10 microliters. A pH sensitive field effect transistor was used as a measuring electrode. Acidification was found to occur in glucose media, while alkalization occurred in the media containing peptone.