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21.
Cell surface T3 expression requires the presence of both alpha- and beta-chains of the T cell receptor 总被引:14,自引:0,他引:14
T Saito A Weiss K C Gunter E M Shevach R N Germain 《Journal of immunology (Baltimore, Md. : 1950)》1987,139(2):625-628
We have identified a surface T3- Jurkat variant which has a defective alpha-chain but which possesses an intact beta-chain. The transfection of a functional mouse alpha-chain into this human T cell induces the expression of surface T3 molecules associated with mouse alpha-human beta-heterodimers detected by anticlonotypic antibodies. Treatment of the transfectant with anti-T3, anti-mouse Ti-alpha, or anti-human Ti-beta antibodies clears all Ti-T3 complexes from the surface. These results demonstrate that functional alpha- and beta-chains are both required for expression of T3 on the cell membrane, and that the Ti heterodimers present and associated with T3 on Jurkat cells involve only alpha- and beta-chains. 相似文献
22.
Evidence from nitrogen-15 and solvent deuterium isotope effects on the chemical mechanism of adenosine deaminase 总被引:1,自引:0,他引:1
We have determined 15N isotope effects and solvent deuterium isotope effects for adenosine deaminase using both adenosine and the slow alternate substrate 7,8-dihydro-8-oxoadenosine. With adenosine, 15N isotope effects were 1.0040 in H2O and 1.0023 in D2O, and the solvent deuterium isotope effect was 0.77. With 7,8-dihydro-8-oxoadenosine, 15N isotope effects were 1.015 in H2O and 1.0131 in D2O, and the solvent deuterium isotope effect was 0.45. The inverse solvent deuterium isotope effect shows that the fractionation factor of a proton, which is originally less than 0.6, increases to near unity during formation of the tetrahedral intermediate from which ammonia is released. Proton inventories for 1/V and 1/(V/K) vs percent D2O are linear, indicating that a single proton has its fractionation factor altered during the reaction. We conclude that a sulfhydryl group on the enzyme donates its proton to oxygen or nitrogen during this step. pH profiles with 7,8-dihydro-8-oxoadenosine suggest that the pK of this sulfhydryl group is 8.45. The inhibition of adenosine deaminase by cadmium also shows a pK of approximately 9 from the pKi profile. Quantitative analysis of the isotope effects suggests an intrinsic 15N isotope effect for the release of ammonia from the tetrahedral intermediate of approximately 1.03 for both substrates; however, the partition ratio of this intermediate for release of ammonia as opposed to back-reaction is 14 times greater for adenosine (1.4) than for 7,8-dihydro-8-oxoadenosine (0.1).(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
23.
The hemodynamic destruction of circulating cancer cells 总被引:2,自引:0,他引:2
L Weiss 《Biorheology》1987,24(2):105-115
The blood-stream is the major disseminative route for metastasizing cancer cells, and metastases are generated when the cancer "microemboli" are trapped in the microcirculation. However, most circulating cancer cells are rapidly destroyed shortly before and/or after arrest. Traditionally, destruction is attributed to the cellular or humoral response of the host defense systems. A novel, non-exclusive mechanism for cancer cell destruction has been proposed by Weiss and Dimitrov in which friction or adhesion between circulating cancer cells and capillary walls causes local vascular blockage, and the blood-pressure differentials normally existing over the entire length of a capillary are consequently applied over the length of the cancer cell. In a simple model, this pressure differential is expected to cause expansion of the cancer cell membrane, resulting in increases in tension above a critical level, with consequent membrane rupture and cell death. In vivo and in vitro experimental tests of this hypothesis are outlined. 相似文献
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25.
Behavioral endocrinology of male rats with periodic sexual contacts with exclusive or varied females
G T Taylor D Komitowski S Muto J Weiss 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1989,192(3):236-241
Sexual contact keys a profound series of acute and chronic changes in males that, presumably, are orchestrated by acute pulsatile release of hormones. An experimental paradigm is reported in which male rats were paired periodically with either the same or different estrous females to receive identical amounts of copulatory experiences. Results confirmed the hypothesis that exposure to an unfamiliar female would induce a different endocrine response which would be reflected in various androgen-sensitive systems. The "successively polygynous" males showed more sexual behavior than "monogamous" males, and their respective females solicited the males differently, as well. Circulating levels of testosterone were higher immediately after sexual contact with an unfamiliar than with a familiar female partner. There were no differences in testosterone titers among the groups when the animals were killed at either 2 or 7 weeks after the final copulatory experiences. Yet, necropsies at 2 weeks postcopulation revealed that primary and secondary sex structures from polygynous males clearly were larger. Differences between the two experimental groups were reduced after 7 weeks of sexual rest, yet, polygnous males continued to show a different structural profile than the other groups. Conclusions were that males may experience greater activation of androgen-sensitive behavior and physiology following qualitatively different sexual contacts. 相似文献
26.
G Debonnel M Weiss C de Montigny 《Canadian journal of physiology and pharmacology》1989,67(8):904-908
Domoic acid, an excitatory amino acid structurally related to kainic acid, has been shown to be responsible for the severe intoxication presented, in 1987, by more than one hundred and fifty people having eaten mussels grown in Prince Edward Island (Canada). Unitary extracellular recordings were obtained from pyramidal neurons of the CA3 region of the rat dorsal hippocampus. The excitatory effects of microiontophoretic applications of domoic acid and of the agonists of the two other subtypes of glutamatergic receptors, quisqualate and N-methyl-D-aspartate, were compared on intact and colchicine-lesioned sides. Similar to what has been previously found for kainate, the colchicine lesion of the mossy fiber projections induced a 95% decrease of the neuronal responsiveness to domoic acid, whereas the effect of quisqualate was unchanged and that of N-methyl-D-aspartate was only slightly decreased. These results provide further electrophysiological evidence that domoic acid is a potent agonist of kainate receptors and that it may produce its neuroexcitatory and neurotoxic effects, in the hippocampal CA3 region, through activation of kainate receptors located on the mossy fiber terminals. 相似文献
27.
Analysis of liver/bone/kidney alkaline phosphatase mRNA, DNA, and enzymatic activity in cultured skin fibroblasts from 14 unrelated patients with severe hypophosphatasia. 总被引:5,自引:2,他引:3 下载免费PDF全文
M J Weiss K Ray M D Fallon M P Whyte K N Fedde M A Lafferty R A Mulivor H Harris 《American journal of human genetics》1989,44(5):686-694
Hypophosphatasia is a heritable disorder characterized by defective bone mineralization and a deficiency of liver/bone/kidney alkaline phosphatase (L/B/K ALP) activity in serum and tissues. Severe forms of the disease, which are generally lethal in infancy, are inherited in an autosomal recessive fashion. The gene defects that produce hypophosphatasia are poorly understood, but many are likely to occur at the L/B/K ALP locus. To investigate these gene defects, we analyzed L/B/K ALP DNA, RNA, and enzyme activity in cultured dermal fibroblasts from 14 patients with perinatal or infantile hypophosphatasia and from 12 normal individuals. Southern blot analyses of the L/B/K ALP genes from patients and controls revealed identical restriction patterns. Control fibroblast ALP activity correlated with the corresponding L/B/K ALP mRNA levels estimated by blot hybridization analysis and densitometry (r = .94, P less than .0001). In contrast, fibroblasts from the hypophosphatasia patients were deficient in ALP enzyme activity but expressed apparently full-sized L/B/K ALP mRNA at normal levels. Bone specimens from one of the patients were examined and found to be deficient in histochemical ALP but contained immunologic cross-reactive material detected by anti-human liver ALP antiserum. Our results demonstrate that the deficiency of ALP activity in fibroblasts from 14 patients with severe hypophosphatasia is not due to decreased steady-state levels of the corresponding mRNA. The presence of enzymatically inactive L/B/K ALP protein in one of these patients is consistent with a point mutation or small in-frame deletion in the coding region of L/B/K ALP gene. 相似文献
28.
Reinhard Lakes Klaus Kalmring Karl-Heinz Engelhard 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1990,166(4):553-563
Deafferentation experiments during postembryonic development show morphological and/or physiological changes of receptor fibers and of identified auditory interneurons in the CNS of the locusts Locusta migratoria and Schistocerca gregaria after unilateral ablation of one tympanic organ either in the larva or the adult animal.
相似文献
1. | In Locusta migratoria, 5 days after deafferentation, intact, contralateral receptor fibers had sprouted collaterals in the frontal acoustic neuropil of the metathoracic ganglion (Figs. 1, 2). Collateral sprouts were only rarely found in Schistocerca gregaria. |
2. | After about 20 days the deafferented auditory interneurons receive new inputs from the contralateral receptors (Figs. 3, 5, 7, 10). This largely restores their thresholds and intensity/response functions. Collaterals from the first order interneurons cross the midline to the contralateral neuropil (BSN1 neuron, Fig. 4), which is never seen in intact animals. By contrast, in the TN1 neuron no consistent morphological change due to the deafferentation could be found (Fig. 6). |
3. | Interneurons of higher order (AN1, TN3 neuron in locusts) regain their response pattern (Fig. 7) without morphological changes (Fig. 9). Bilateral recordings show that the deafferented interneurons respond more weakly to auditory stimuli than the intact neuron, but the response to vibration stimuli remains unchanged (TN3 neuron, Fig. 8). |
29.
30.
The receptive fields of complex neurons within area 18 of the cerebral cortex of the cat were determined by a computer-assisted method using a moving light bar substantially shorter than the long diameter of the receptive field as a visual stimulus. The visual cells repeatedly generated nerve impulses when the stimulus crossed well-defined active points within their receptive fields. Outside of these active points, the cells remained silent. It is suggested that the receptive fields are formed by a discontinuous accumulation of such active points. When the electrical activities of two neighbouring visual neurons are recorded simultaneously, their active points do not coincide. In addition, some active points were located outside the most prominent excitatory part of the receptive field of the studied cells. Individual visual cells typically differ in the number and distribution of active points. Since these cells best respond to a stimulus moving in a certain direction, it is suggested that they may act as direction of movement and/or velocity detectors. Alternate firing of a number of neighboring cells connected to a distributed pattern of peripheral receptors may form a system which is able to code for velocity and direction of the moving stimulus. 相似文献