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991.
In attempts to determine the mechanism of proliferation of arterial smooth muscle cells (SMC) in intimal atheromatous lesions, autocrine secretion of growth factors by SMC has recently received much attention. Here we report a new growth factor named smooth muscle cell derived growth factor (SDGF). Cultured rabbit medial SMC secreted SDGF for 1 week during their incubation in serum-free media only after at least 4 passages. SDGF differed from platelet derived growth factor (PDGF) physicochemically, immunologically, and biologically. The properties of SDGF also seemed different from those of other known growth factors that stimulate the proliferation of mesenchymal cells. 相似文献
992.
The subcellular distribution in rat hepatocytes of enzymes participating in the entire generation cycle of phosphatidylinositol 4,5-bisphosphate, and phosphorylated intermediates of this pathway, has been examined by Nycodenz gradient centrifugation. Our results indicate that the synthesis of phosphatidylinositol takes place in the endoplasmic reticulum, and that its phosphorylation to phosphatidylinositol 4-phosphate occurs intracellularly in low-density membranes before translocation to the plasma membrane, where it is further phosphorylated to phosphatidylinositol 4,5-bisphosphate. The intracellular formation of PIP implies a vesicular transport to the plasma membrane. 相似文献
993.
A B Van Kuilenburg A O Muijsers H Demol H L Dekker J J Van Beeumen 《FEBS letters》1988,240(1-2):127-132
Subunit VIII was purified from a preparation of the human heart cytochrome c oxidase and its complete amino acid sequence was determined. The sequence proved to be much more related to that of the bovine liver oxidase subunit VIII than to that found in bovine heart. Our finding of a ‘liver-type’ subunit VIII in the human heart enzyme suggests that either there are no isoforms of human subunit VIII or the human oxidase does not show the type of tissue specificity that has been reported for the oxidase in other mammals. 相似文献
994.
The activating anions are found to induce an unexpectedly high (up to 8-fold for sulphite) increase of ATPase activity in intact rat liver mitochondria. This effect is not determined by the observed changes in Km and Ki (ADP) values. The stimulation seems to be caused by dissociation of the inactive complex of ATPase with Mg·ADP. The quantity of this complex formed in the course of ATP hydrolysis is approx. 90% of the total ATPase content in intact mitochondria. The data on toluene-permeabilized mitochondria suggest that the high content of the complex is a result of the stabilizing effect of some matrix macromolecules. 相似文献
995.
Christophe N. N'soukpo-Kossi Jan Sielewiesiuk Roger M. Leblanc Richard A. Bone John T. Landrum 《生物化学与生物物理学报:生物膜》1988,940(2)
The linear dichroism of single monolayers of lutein, zeaxanthin and a mixture of lutein and synthetic phosphatidylcholine has been measured. The angle of orientation of the carotenoid molecules was found to lie between 45° and 51° relative to the plane of the solid support. Although the adsorbed monolayers were mostly in a monomeric state, microscopic observations, as well as the II-A isotherms, indicated the existence of crystalline islets. The results have been interpreted in connection with Haidinger's polarization brushes. 相似文献
996.
Hideto Kuwayama 《生物化学与生物物理学报:生物膜》1988,940(2)
The effect of membrane potential on the activity of the ATP-dependent Ca2+ pump of isolated canine ventricular sarcolemmal vesicles were investigated. The membrane potential was controlled by the intravesicular and extravesicular concentration of K+, and the initial rates of Ca2+ uptake both in the presence and the absence of valinomycin were determined. The rate of Ca2+ uptake was stimulated by a inside-negative potential induced in the presence of valinomycin. The valinomycin-dependent stimulation was enhanced by the addition of K+ channel blocker, tetraethylammonium ion or Ba2+. The electrogenicity of cardiac sarcolemmal ATP-dependent Ca2+ pump is suggested from the increase of Ca2+ uptake by negative potential induced by valinomycin. 相似文献
997.
Synaptosomes isolated from the rat cerebral cortex were mixed with sonicated phospholipid vesicles and subjected to freezing-thawing to acquire giant proteoliposomes. Membranes of these giant proteoliposome could thus be studied using patch-clamp techniques. Single-channel currents were measured with the inside-out patch of the membrane, in KCl solutions. Three different potassium channels were detected and unit conductances were 15.1, 28.6 and 91.0 pS, respectively, in a symmetrical 150 mM KCl solution. All these channels are more permeable to potassium than to sodium ions, the permeability ratio being about 2:1. Tetraethylammonium ions blocked these channels. The gating of these potassium channels is independent of the membrane potential, Presumably, these channels play a role in the resting membrane potential of presynaptic nerve terminals. 相似文献
998.
The components of magnesium efflux in squid axons have been studied under internal dialysis and voltage clamp conditions. The present report rules out the existence of an ATP-dependent, Na0- and Mg0-independent Mg2+ efflux (ATP-dependent Mg2+ pump) leaving the Mg2+---Na+ exchange system as the only mechanism for Mg2+ extrusion. The main features of the Mg2+ efflux are: (1) The efflux is completely dependent on ATP. (2) The efflux can be activated either by external Na+ (forward Mg2+---Na+ exchange) or external Mg2+ (Mg2+---Mg2+ exchange). (3) The mobility of the Mg2+ exchanger in the Na0+-loaded form is greater than that in the Mg2+-loaded one. (4) In variance with the Na+---Ca2+ exchange mechanism, Mg2+---Mg2+ exchange is not activated by external monovalent cations. (5) ATPγS replaces ATP in activating Mg2+---Na+ exchange suggesting that a phosphorylation/dephosphorylation process regulates this transport mechanism. 相似文献
999.
Myocardial sodium-pump activity was examined from ouabain-sensitive 86Rb+ uptake using myocytes isolated from guinea-pig heart. Either sodium loading or the sodium ionophore, monensin, increased 86Rb+ uptake by over 400%, indicating that the amount of Na+ available to the pump is the primary determinant of its activity, and that the sodium pump has a substantial reserve capacity in quiescent myocytes. Moreover, the degree of the above stimulation is markedly higher than corresponding values reported with multicellular preparations, suggesting that diffusion barriers make it impossible to observe the capacity of the sodium pump in the latter preparations. Removal of extracellular Ca2+ increased ouabain-sensitive 86Rb+ uptake, probably by enhancing turnover of the sodium pump rather than increasing availability of Na+ to the pump. 相似文献
1000.
A series of experiments were conducted to characterize patterns of eclosion by Bemisia tabaci (Genn.) (Homoptera: Aleyrodidae) to their adult stage and to determine how these patterns are influenced by certain environmental parameters. Under a constant temperature of 29.5±0.6°C and a photoperiod of 14:10LD, 90% of the adults emerged from their pupal cases between 0600 and 0930 h (with lights on occurring at 0600 h). Few emerged during hours of darkness. The peak time of adult emergence was delayed when temperatures were fluctuated. Under a series of constant temperatures, a significant inverse correlation was found between the time of median emergence (i.e., eclosion of 50% of the total number of adults) and temperature (P<0.001). No emergence was observed at temperatures below 17±0.3°C. Emergence patterns persisted under conditions of continuous light and continuous darkness, suggesting the presence of a circadian system.
Zusammenfassung Um das Verständnis über den Lebenslauf von Bemisia tabaci zu ergänzen, wurde eine Serie von Experimenten durchgeführt, deren Zweck die Charakterisierung des Ausschlüpfvorgangs in das Endstadium war und die Feststellung, wie dieser Vorgang von gewissen Umweltparametern beeinflusst wird. Bei einer konstanten Temperatur von 29.5±0.6°C und einem Beleuchtungszyklus von 14: 10 LD (Licht/Dunkelheit) schlüpften 90% der Ausgewachsenen zwischen 0600 Uhr and 0930 Uhr (ab 0600 Uhr mit Licht) aus ihren Puppenhüllen aus. Wenig Ausschlüpfen geschah während der unbeleuchteten Stunden. Der Höhepunkt des Ausschlüpfens wurde bei wechselnden Temperaturen verschoben. Bei einer Serie von gleichbleibenden Temperaturen wurde eine bedeutende inverse Korrelation zwischen der medianen Ausschlüpfzeit (d.h. 50% der gesamten Ausgewachsenen schlüpften aus) und der Temperatur festgestellt (P<0.001). Kein Ausschlüpfen wurde beobachtet bei Temperaturen unter 17°C. Das Ausschlüpfschema war gleichbleibend bei dauerndem Licht oder dauernder Dunkelheit, was auf das Vorhandensein eines circadianen Systems hinweist.相似文献