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1.
The osmium-dimethyl sulfoxide-osmium method for clear visualization of intracellular structure was used to observe the detailed inner structure of the spherical bodies produced in vitro by a human oral treponeme. Scanning electron microscopy of the cracked spherical body revealed no morphological differences between the outer and inner surfaces of the spherical body membrane, and that multiple folded or somewhat linear main bodies adhere closely to the inner surface. In addition, axial flagella partially free from the main bodies spread widely within the body to make a network, and a number of blebs ranging from approximately 1 μm to 0.2 μm in diameter were located near the terminal or subterminal areas of the main bodies. The origin of the blebs and the mechanism of spherical body formation are discussed.  相似文献   
2.
Aggregatibacter actinomycetemcomitans is considered to be associated with periodontitis. Leukotoxin (LtxA), which destroys leukocytes in humans, is one of this bacterium's major virulence factors. Amounts of neutrophil elastase (NE), which is normally localized in the cytoplasm of neutrophils, are reportedly increased in the saliva of patients with periodontitis. However, the mechanism by which NE is released from human neutrophils and the role of NE in periodontitis is unclear. In the present study, it was hypothesized that LtxA induces NE release from human neutrophils, which subsequently causes the breakdown of periodontal tissues. LtxA‐treatment did not induce significant cytotoxicity against human gingival epithelial cells (HGECs) or human gingival fibroblasts (HGFs). However, it did induce significant cytotoxicity against human neutrophils, leading to NE release. Furthermore, NE and the supernatant from LtxA‐treated human neutrophils induced detachment and death of HGECs and HGFs, these effects being inhibited by administration of an NE inhibitor, sivelestat. The present results suggest that LtxA mediates human neutrophil lysis and induces the subsequent release of NE, which eventually results in detachment and death of HGECs and HGFs. Thus, LtxA‐induced release of NE could cause breakdown of periodontal tissue and thereby exacerbate periodontitis.  相似文献   
3.
Summary I study the evolutionarily stable seasonal patterns of hatching and pupation for herbivorous insects that engage in exploitative competition for a renewable resource. A longer larval feeding period enhances female fecundity, but also causes a higher mortality by predation and parasitism. Previously, it was shown that the evolutionarily stable population exhibits asynchronous starting and ending of the larval feeding period in a model in which larval growth rate decreases with the total larval biomass in the population due presumably to interference competition. Here I study the case in which resource availability changes not only with environmental seasonality but with the depletion by the feeding of larvae. I find that if the impact of the herbivory is strong, both hatching and pupation should occur asynchronously in the evolutionarily stable population. And if the favourable season for the host plant is short the ESS population may include synchronous timing of pupation. If the timing of hatching and pupation occurs asynchronously, in the first day of each interval some fraction of the population hatch or pupate, respectively and the rest do so gradually over the interval. In addition, if the environmental variable changes as a symmetric function of time, the length of the period in which hatching occurs tends to be much shorter than the period in which pupation occurs.  相似文献   
4.
Horizontal distribution of the dinoflagellateCeratium hirundinella (O. F. Müller) Bergh in the Ishitegawa Reservoir, Ehime Prefecture, Japan, was investigated. Water quality was also surveyed. It was observed that the population ofC. hirundinella exponentially decreased in number from the head of the reservoir to the dam site. Further investigation proved thatC. hirundinella initiated growth at the head of the reservoir, and later gradually expanded downstream. It was found during the period of increase in water temperature that the cell density ofC. hirundinella at the uppermost station exponentially increased.  相似文献   
5.
Using four continuous-flow indoor reservoir models, the combined effects of varying water inlet depth and sediment composition on phytoplankton species composition and its succession pattern were studied. Species which are known to bloom in eutrophicated reservoirs were dominant in the species succession in each tank. At any one time, a step-like pattern was observed in the composition of the dominant species of each tank, wherein all the species which appeared in a tank with a lower phosphorus concentration were included in the species composition of the tank with a higher phosphorus concentration in an additive relationship.  相似文献   
6.
Abstract: In cultured bovine adrenal medullary cells, stimulation of nicotinic receptors by carbachol evoked the Ca2+-dependent exocytotic cosecretion of proadrenomedullin N-terminal 20 peptide (PAMP) (EC50 = 50.1 µ M ) and catecholamines (EC50 = 63.0 µ M ), with the molar ratio of PAMP/catecholamines secreted being equal to the ratio in the cells. Addition of PAMP[1–20]NH2 inhibited carbachol-induced 22Na+ influx via nicotinic receptors (IC50 = 2.5 µ M ) in a noncompetitive manner and thereby reduced carbachol-induced 45Ca2+ influx via voltage-dependent Ca2+ channels (IC50 = 1.0 µ M ) and catecholamine secretion (IC50 = 1.6 µ M ). It did not alter high K+-induced 45Ca2+ influx via voltage-dependent Ca2+ channels or veratridine-induced 22Na+ influx via voltage-dependent Na+ channels. PAMP seems to be a novel antinicotinic peptide cosecreted with catecholamines by a Ca2+-dependent exocytosis in response to nicotinic receptor stimulation.  相似文献   
7.
I Mak  H Ezoe    S Mak 《Journal of virology》1979,32(1):240-250
Purified human adenovirus type 12 preparations contain defective virions with a lighter density. These defective virions were isolated, and their biological functions and DNA were characterized. They can induce early and late antigens in infected cells and tumors in newborn hamsters with similar efficiency as complete virions. The majority of the DNA molecules from light virions contain deletions mapping near 16% from the left-hand end of the genome. Mechanisms for the generation of these molecules are discussed.  相似文献   
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