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E. Y. Lasfargues Dan H. Moore Margaret R. Murray Cushman D. Haagensen E. C. Pollard 《The Journal of cell biology》1959,5(1):93-95
Thin sections of tissue cultures grown from tumors of the RIII high-breast-cancer strain mice were studied in the electron microscope. These tissues contain an abundance of particles whose morphology is consistent with biophysical measurement of the milk agent. These particles, found only extracellularly in our cultures, are formed at the cell membrane. The process of formation, as reconstructed from sections, appears to include a thickening and protrusion of the cell membrane which then evolves gradually into a dense sphere and separates from the cell in much the same manner as does influenza virus. The contents of the newly formed body are later rearranged to form a nucleoid within a membranous sac. 相似文献
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Saxifraga marginata Sternb. is divided into three subspecies:S. m. subsp.marginata, S. m. subsp.bubakii (Rohlena)Chrtek etSoják,S. m. subsp.karadzicensis (Degen etKo?anin)Chrtek etSoják (environments of Skopje, Macedonia). 相似文献
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This study examined the morphological development of single inhibitory arborizations in the gerbil central auditory brain stem. Using a brain slice preparation, neurons of the medial nucleus of the trapezoid body (MNTB) were filled with horseradish peroxidase (HRP), and their complete arborizations were analyzed along the tonotopic axis of the lateral superior olive (LSO). The projections in neonatal animals displayed well-defined arbors that were ordered appropriately within the LSO. It was evident from the axonal pathways that the MNTB afferents could correct for projection errors after reaching the postsynaptic population. As development progressed, a number of arbors established diffuse or inappropriate projections within the LSO. These immature arborizations were no longer apparent by 18–25 days postnatal. The anatomical specificity of arbors at 12–13 and 18–25 days was quantified by measuring the distance that terminal boutons spread across the frequency axis. There was a significant reduction of this distance in older animals. In addition, there was a significant reduction in the mean number of boutons per arbor between 12–13 days and 18–25 days. The maximum nucleus cross-sectional area continued to increase through 15–16 days, indicating that the refined arbors occupied an even smaller fraction of the postsynaptic structure. Taken together, these observations suggest that central inhibitory arbors form exuberant contacts that must be eliminated during development. 相似文献
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Summary Plasminogen activator inhibitor type-1 (PAI-1) was identified in extracts of rat adrenal medulla, and its immunohistochemical localization was studied together with that of tissue-type plasminogen activator (t-PA). By staining of adjacent sections and by doublestaining of the same section we demonstrate that the same cells of the adrenal medulla contain both PAI-1 and t-PA immunoreactivity in the cytoplasm. In addition a few ganglion cells of the adrenal medulla were found to contain PAI-1 but not t-PA. Neither of the components were found in the adrenal cortex. Analysis of extracts from isolated adrenal medulla using reverse zymography showed the presence of a plasminogen activator inhibitor with M
r46000. The inhibitory activity disappeared when the extract was passed through a column with sepharose-coupled anti-PAI-1 IgG, while the run-through from a similar column coupled with preimmune IgG still contained the inhibitor. The present findings suggest that PAI-1 could play a role in the regulation of t-PA activity in the rat adrenal gland medullary cells. 相似文献
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Hubert Wiener Dan A. Klaerke Peter L. Jørgensen 《The Journal of membrane biology》1990,117(3):275-283
Summary In the mammalian distal colon, the surface epithelium is responsible for electrolyte absorption, while the crypts are the site of secretion. This study examines the properties of electrical potential-driven86Rb+ fluxes through K+ channels in basolateral membrane vesicles of surface and crypt cells of the rabbit distal colon epithelium. We show that Ba2+-sensitive, Ca2+-activated K+ channels are present in both surface and crypt cell derived vesicles with half-maximal activation at 5×10–7
m free Ca2+. This suggests an important role of cytoplasmic Ca2+ in the regulation of the bidirectional ion fluxes in the colon epithelium.The properties of K+ channels in the surface cell membrane fraction differ from those of the channels in the crypt cell derived membranes. The peptide toxin apamin inhibits Ca2+-activated K+ channels exclusively in surface cell vesicles, while charybdotoxin inhibits predominantely in the crypt cell membrane fraction. Titrations with H+ and tetraethylammonium show that both high-and low-sensitive86Rb+ flux components are present in surface cell vesicles, while the high-sensitive component is absent in the crypt cell membrane fraction. The Ba2+-sensitive, Ca2+-activated K+ channels can be solubilized in CHAPS and reconstituted into phospholipid vesicles. This is an essential step for further characterization of channel properties and for identification of the channel proteins in purification procedures. 相似文献
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昆虫是森林生态系统中的重要组成部分。由于森林中枯枝落叶较多,生境复杂,为昆虫提供了良好的繁殖和栖息场所;因而在森林中昆虫的种类多,数量大。大多数昆虫都以森林 相似文献