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291.
Inositol 1,4,5-trisphosphate activates a channel from smooth muscle sarcoplasmic reticulum 总被引:35,自引:0,他引:35
Inositol 1,4,5-trisphosphate (InsP3) can initiate calcium release into the cytoplasm in a variety of cells. From experiments using permeabilized cells, membrane vesicles, and patch-clamp techniques, it has been suggested that InsP3 acts by directly opening calcium channels. Here, we show that InsP3 induced openings of channels in planar lipid bilayers into which vesicles made from aortic muscle sarcoplasmic reticulum (SR) were incorporated. Activation of channels by InsP3 was not observed when vesicles made from SR of cardiac or skeletal muscle were incorporated into planar lipid bilayers. The present study demonstrates for the first time unique properties of an InsP3-gated calcium channel in sarcoplasmic reticulum vesicles from vascular smooth muscle. This InsP3-activated channel from aortic SR differs strikingly from the calcium-gated calcium channel of striated muscle SR in single-channel conductance and pharmacology. 相似文献
292.
The function and structure of the metal coordination sites within the glucocorticoid receptor DNA binding domain 总被引:54,自引:0,他引:54
L P Freedman B F Luisi Z R Korszun R Basavappa P B Sigler K R Yamamoto 《Nature》1988,334(6182):543-546
293.
Incubation periods for paediatric AIDS patients 总被引:11,自引:0,他引:11
I Auger P Thomas V De Gruttola D Morse D Moore R Williams B Truman C E Lawrence 《Nature》1988,336(6199):575-577
A recent seroprevalence study of newborns indicates that one in 62 children born in New York City has antibodies to the human immunodeficiency virus (HIV). The distribution of incubation periods for paediatric patients is needed to estimate future AIDS case loads from these seroprevalence data. Current estimates of incubation periods for paediatric patients are based on limited data. We use parametric and non-parametric methods to analyse incubation periods for 215 paediatric patients with AIDS whose only known route of infection is maternal. We conclude that incubation periods are longer than previously reported; that there is a distinct knee in the incubation period distribution at seven months which suggests two risk populations; and that there is an increase in incidence which is consistent with exponential growth. 相似文献
294.
B E Saether 《Nature》1988,331(6157):616-617
A large amount of variation is found in most reproductive traits of birds. Clutch size for instance, can vary from 1 to 15 between species of similar body weight. The adaptive significance of this variation is only poorly understood. According to life-history theory, large clutch size and early onset of reproduction are expected when the chances of survival are low. There is some support for the existence of such a relationship from studies of single species. Here I present evidence that, in European birds, clutch size is increased, and onset of reproduction occurs earlier in life, when the probability of survival is low. 相似文献
295.
Noradrenaline (NA) regulates arterial smooth muscle tone and hence blood vessel diameter and blood flow. NA apparently increases tone by causing a calcium influx through the cell membrane. Two calcium influx pathways have been proposed: voltage-activated calcium channels and NA-activated calcium-permeable channels that are voltage-insensitive. Although voltage-activated calcium channels have been identified in arterial smooth muscle, voltage-insensitive calcium channels activated by NA have not. We show here that NA contractions of rabbit mesenteric arteries increase with depolarization. The increase parallels the elevation of open-state probability (P0) of single, voltage-dependent calcium channels. The action of noradrenaline can be explained by NA-activating voltage-dependent calcium channels, rather than by opening a second type of channel. We show directly that NA increases the open-state probability of single calcium channels. Thus, in the presence of NA, calcium entry through voltage-dependent calcium channels can regulate smooth muscle tone at physiological membrane potentials. These results may have relevance to pathophysiological conditions such as hypertension. 相似文献
296.
We compared the effects of 0.45% normal saline (NS), 5% Intralipid® (IL), and 16.7% glucose (Glu) infusions on total serum triglycerides and cholesterol, serum high-(HDL-c) and low-density lipoprotein cholesterol (LDL-c), and activity of serum lecithin: cholesterol acyltransferase (LCAT), and serum lipoprotein lipase (LPL) in rats implanted with a fibrosarcoma. In tumor-bearing rats given NS, a two-fold increase in total serum cholesterol, a four-fold increase in LDL-c, and a five-fold decrease in the HDL-c/LDL-c ratio were observed compared to tumor-free rats. In tumor-bearing rats administered IL, a two-fold increase in total serum triglyceride and cholesterol, a three-fold increase in HDL-c and HDL-c/LDL-c ratio, and a two-fold increase in LPL activity were observed compared to tumor-bearing rats administered NS. In tumor-bearing rats administered Glu, a two-fold decrease in total serum cholesterol, a two-fold decrease in HDL-c, and a three-fold decrease in LDL-c were observed compared to tumor-bearing rats administered NS. Tumor weights and LCAT activity did not differ significantly between treatment groups. Previous results have demonstrated that lipophilic compounds that interact with plasma lipoproteins have altered pharmacological effects when administered with IL. Therefore, this study suggests that IL infusions alter the HDL-c/LDL-c ratio and could affect the pharmacological behavior of anticancer compounds that predominantly distribute into the LDL fraction upon entrance into the bloodstream. 相似文献
297.
本文使用SEM、EDS、EAS、XRD和电阻率测量技术,研究了工艺参数和加入(Co,Fe2O3)对PTC(V1-x,Crx)2O3陶瓷的显微结构和电性能的影响。实验结果表明,为了制造优良性能、高可靠的热敏电阻器,必须精确控制陶瓷组份和工艺。引人象C。这样的添加物是重要的,它主要以金属形式分布在基体中,同时发现添加物对试样致密度和电性能的影响也是有益的。 相似文献
298.
Monoclonal antibody and ligand binding sites of the T cell erythrocyte receptor (CD2) 总被引:4,自引:0,他引:4
The human T cell erythrocyte receptor (CD2 antigen) allows thymocytes and mature T cells to adhere to thymic epithelium and target cells through a cell surface protein, LFA-3 (refs 1-6). Monoclonal antibodies recognizing CD2 can either block adhesion or, in certain combinations, induce an antigen-independent T cell activation. We have identified the binding sites for 16 monoclonal antibodies against CD2 by a rapid and generally applicable mutational analysis. The binding sites fall in three discrete regions: antibodies that participate in activation and block erythrocyte adhesion bind to the first region; antibodies that block adhesion bind to the second region; and antibodies that participate in activation but do not block adhesion bind to the third region. A large number of mutations selected for loss of antibody reactivity in the first two regions also weaken the CD2-LFA-3 interaction. Good agreement was observed between mutational lesions blocking LFA-3 binding and lesions blocking binding by activating antibodies, which supports the view that such antibodies induce T cell activation by mimicking the effect of LFA-3 binding. CD2 sequences that participate in LFA-3 binding correspond to immunoglobulin variable region hypervariable sequences when the homologous domains are aligned. 相似文献
299.
An AIDS-related cytotoxic autoantibody reacts with a specific antigen on stimulated CD4+ T cells 总被引:2,自引:0,他引:2
R B Stricker T M McHugh D J Moody W J Morrow D P Stites M A Shuman J A Levy 《Nature》1987,327(6124):710-713
Patients with the acquired immune deficiency syndrome (AIDS) and AIDS-related conditions are known to have abnormalities of T cell subpopulations, including a decreased helper/inducer (bearing the CD4 antigen) to suppressor/cytotoxic (bearing the CD8 antigen) T cell ratio and decreased absolute numbers of T cells with the CD4+ phenotype. Infection of T cells with a retrovirus, termed human immunodeficiency virus (HIV), is thought to be important in these abnormalities. HIV infection alone does not adequately explain the CD4+ T-cell abnormalities seen in AIDS, however, and the nature of T-cell destruction in this disease remains poorly characterized. Here we describe an AIDS-related serum autoantibody that reacts with an antigen of relative molecular mass 18,000 (Mr 18K) restricted to lectin-stimulated or HIV-infected CD4+ T cells. The antibody also suppresses proliferation of CD4+ T cells in vitro and induces cytotoxicity of these cells in the presence of complement. Its role in the development of AIDS merits attention. 相似文献
300.
The cell-cycle regulated proliferating cell nuclear antigen is required for SV40 DNA replication in vitro 总被引:87,自引:0,他引:87
Cell-free extracts prepared from human 293 cells, supplemented with purified SV40 large-T antigen, support replication of plasmids containing the SV40 origin of DNA replication. A cellular protein (Mr approximately 36,000) that is required for efficient SV40 DNA synthesis in vitro has been purified from these extracts. This protein is recognized by human autoantibodies and is identified as the cell-cycle regulated protein known as proliferating cell nuclear antigen (PCNA) or cyclin. 相似文献