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31.
Action potentials and isometric force were recorded in papillary muscles from guinea pigs and summer hedgehogs at different temperatures between 37 and 0 degrees C. The action potential of the hedgehog was of a lower amplitude (mean 83 +/- 6 mV) than that of the guinea pig (mean 110 +/- 5 mV). The action potential duration at 50% repolarization was 22 +/- 2 msec in the hedgehog as compared to 105 +/- 11 msec in the guinea pig. Moreover, there was no distinct plateau phase of the hedgehog action potential. Lowering temperature prolonged the action potential duration in the two preparations by about the same percentage. However, the guinea pig preparation became progressively less excitable below 20 degrees C. Lowered temperature produced a positive inotropic effect in the guinea pig, whereas this effect was very slight in the hedgehog heart. Postextrasystolic potentiation was seen in the guinea pig but not in the hedgehog preparation. It is suggested that this difference between the preparations may be due to a greater relative amount of activator calcium in the hedgehog heart. The difference in cold tolerance between the preparations may reflect a difference in chemical composition of the sarcolemma. 相似文献
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Representative facultative anaerobes of the bacterial flora from the intestine of female Ascaris suum were isolated and identified. The number of bacteria in the intestine was approximately 4 X 10(9) per g wet weight of intestine. Seventeen of 19 of the isolated colonies were found to secrete 5-hydroxytryptamine in culture. Holding A. suum in an antibiotic-containing medium did not affect the levels of 5-hydroxytryptamine in the worm, which were 231 +/- 14 ng/g in antibiotic-media as compared to 250 +/- 16 ng/g in control media. This implied that the bacteria may not be contributing to the level of 5-hydroxytryptamine in the tissues of A. suum. 相似文献
35.
Data are presented on the aboveground and underground biomass of the speciesMarsilea quadrifolia and on the water regime and soil conditions in a habitat of this species in Central Europe (Czechoslovakia). 相似文献
36.
Concentrations of Cu, Ag and Zn were measured in the soft tissues of the estuarine bivalve Macoma balthica in South San Francisco Bay at near-monthly intervals for periods of two to three years at four stations, and eight years at a metal-enriched station. The amplitude and frequency of fluctuations differed among stations and among metals. Fluctuations were greatest at stations with the greatest metal enrichment and with the least dilution and flushing of wastes. A consistent seasonal pattern of fluctuation in Cu and Ag concentrations was evident in M. balthica at the metal-enriched station. These seasonal changes in tissue metal concentrations appeared to be affected by metal inputs, hydrologic processes that may affect both metal concentrations and bioavailability, and seasonal changes in the weight of the bivalve. The contributions of each of these interacting factors could not be determined quantitatively. At the metal-enriched station significant variation in the amplitude of seasonal fluctuations was also evident from year to year. Interpretation of metal concentrations in bivalves from estuaries will require careful consideration of the processes which affect metal dynamics in these complex environments. 相似文献
37.
Heikki O. Laurila Helena Nevalainen Veijo Mäkinen 《Applied microbiology and biotechnology》1985,21(3-4):210-212
Summary Protoplast formation in Curvularia inaequalis was achieved using non-commercial and commercial snail gut enzymes or Trichoderma harzianum enzymes. The cells were grown for enzyme treatment on cellophane sheets or in liquid cultures for varying periods of time. The production of T. harzianum enzymes is discussed. The highest protoplast yields were 2.6x107 protoplasts/ml enzyme solution. Protoplasts were shown to have zero to four nuclei. Protoplast regeneration was succesfully carried out in semisolid agar. 相似文献
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Photosynthesis and nitrogen utilization in exponentially growing nitrogen-limited cultures of Lemna gibba 总被引:2,自引:0,他引:2
The photosynthetic performance and nitrogen utilization of Lemna gibba L. G3 adapted to limited nitrogen supply was studied. The plants were adapted to two levels of nitrogen limitation where the nitrogen addition rates were calculated to sustain relative growth rates (RGR) of 0.15 day?1 and 0.25 day?1, respectively. The photosynthetic performance of these cultures was compared to nitrogen-sufficient cultures with an average RGR of 0.32 day?1. Plants transferred from nitrogen-sufficient conditions attained RGR values corresponding to the nitrogen addition rates after 6 to 10 days. Light-saturated net photosynthesis declined during adaptation according to the drop in growth rate, and a concomitant decrease in the respiration rate was recorded. The efficiency of net photosynthesis on a dry weight basis increased with increased nitrogen supply, whereas it was the same in all cultures when expressed on a chlorophyll basis. The light compensation point was unaffected by the nitrogen regime. Limited nitrogen supply resulted in an increased proportion of dry matter in the roots, which led to decreased leaf area ratios. The net assimilation rates also decreased, but not to the same extent as the leaf area ratios. Growth-limiting amounts of nitrogen were added to the cultures once daily, and the net influx of N was higher than the requirement for N, also in adapted cultures with a steady growth rate. This resulted in transient, periodic fluctuations in the NO3?, NH4+ and amino acid pools. Also the rates of NO3? reduction and NH4+ assimilation fluctuated as did the amino acid assimilation which paralleled NH4+ assimilation. The role of flux rates over the plasmalemma and tonoplast for control of nitrogen assimilation rates are discussed. 相似文献
40.
Meria E. Penttilä K. M. Helena Nevalainen Alain Raynal Jonathan K. C. Knowles 《Molecular & general genetics : MGG》1984,194(3):494-499
Summary The possibility of cloning filamentous fungal genes by expression in the yeast Saccharomyces cerevisiae has been studied. A genome bank of Aspergillus niger was made in E. coli using a yeast cosmid shuttle vector and over 10,000 different cosmid clones were individually isolated. Yeast transformants carrying Aspergillus DNA were screened for the expression of the genes for fungal secreted glycoproteins, -galactosidase, -glucosidase, and amyloglucosidase, and for the expression of fungal genes complementing yeast ura3 and leu2 mutations.Of the five Aspergillus genes studied, only one, -glucosidase, was found to be expressed in yeast, and this at a low level. This suggests that there are essential differences between the genes of yeast and filamentous fungi. 相似文献