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61.
To probe the structure-function relationships of voltage-dependent sodium channels, we have been examining the mechanisms of channel modification by batrachotoxin (BTX), veratridine (VTD), and grayanotoxin-I (GTX), investigating the unifying mechanisms that underlie the diverse modifications of this class of neurotoxins. In this paper, highly purified sodium channel polypeptides from the electric organ of the electric eel were incorporated into planar lipid bilayers in the presence of GTX for comparison with our previous studies of BTX (Recio-Pinto, E., D. S. Duch, S. R. Levinson, and B. W. Urban. 1987. J. Gen. Physiol. 90:375-395) and VTD (Duch, D. S., E. Recio-Pinto, C. Frenkel, S. R. Levinson, and B. W. Urban. 1989. J. Gen. Physiol. 94:813-831) modifications. GTX-modified channels had a single channel conductance of 16 pS. An additional large GTX-modified open state (40-55 pS) was found which occurred in bursts correlated with channel openings and closings. Two voltage-dependent processes controlling the open time of these modified channels were characterized: (a) a concentration-dependent removal of inactivation analogous to VTD-modified channels, and (b) activation gating similar to BTX-modified channels, but occurring at more hyperpolarized potentials. The voltage dependence of removal of inactivation correlated with parallel voltage-dependent changes in the estimated K1/2 of VTD and GTX modifications. Ranking either the single channel conductances or the depolarization required for 50% activation, the same sequence is obtained: unmodified > BTX > GTX > VTD. The efficacy of the toxins as activators follows the same ranking (Catterall, W. A. 1977. J. Biol. Chem. 252:8669-8676). 相似文献
62.
In vivo and in vitro effects of boron on the plasma membrane proton pump of sunflower roots 总被引:3,自引:0,他引:3
Marta Roldán rés Belver Pilar Rodríguez-Rosales Nuria Ferrol Juan Pedro Donaire 《Physiologia plantarum》1992,84(1):49-54
The effect of boron excess and deficiency on H+ efflux from excised roots from sunflower ( Heliarahus annuus L. cv. Enano) seedlings and on plasma membrane H+ -ATPase (EC 3.6.1.35) in isolated KI-washed microsomes has been investigated. When seedlings were grown in media with toxic levels of H3 BO3 (5 m M ) or without added boron and exposed to light conditions, an inhibition of the capacity for external acidification by excised roots was observed as compared to roots from seedlings grown with optimal H3 BO3 concentration (0.25 m M ). Toxic and deficient boron conditions also inhibited the vanadate-sensitive H+ -ATPase of microsomes isolated from the roots. The mechanism of boron toxicity was investigated in vitro with microsorne vesicles. A strong effect of boron on the vanadate-sensitive, ATP-dependent H+ transport was found, but the vanadate-sensitive phospho-bydrolase activity was not affected. These results suggest that boron could exert an effect on the plasma membrane properties, directly or indirectly regulating, proton transport. 相似文献
63.
Soledad Gaitán Elvira Cuenllas Pilar Sancho Juan A. Bueren Concepción Tejero 《Bioscience reports》1992,12(4):281-292
This paper analyzes the long-term (6 and 12 months) function of mouse granulocytes after total body irradiation with a single dose (5 Gy) of X-rays. Superoxide anion production has been investigated in granulocytes from peripheral blood, and also in those harvested from long term bone marrow cultures, with the aim of correlating the environmental damage induced by radiation with the functional properties of granulocytes. Anin vivo andin vitro enhancement of superoxide anion production and protein levels in granulocytes from irradiated mice is described. The presence of some colony stimulating factor in the supernatant of cultures from irradiated mice could play an important role in the priming of granulocytes. 相似文献
64.
Pilar Galan Helene Thibault Paul Preziosi Serge Hercberg 《Biological trace element research》1992,32(1-3):421-426
The relationship between iron status and capacity for IL-2 production by lymphocytes was assessed in 81 children from 6 mo
to 3 yr of age selected at random from a population with low socioeconomic status, undergoing free systematic examination
in four children's health centers in the Paris area. Iron deficiency was defined by the existence of at least two abnormal
values among the three indicators of iron status: serum ferritin level ≤12 μg/L, transferrin saturation <12%, and erythrocyte
protoporphyrin concentration >3 μg/g hemoglobin. According to this definition, 53 children were classified as iron deficient
and 28 as iron sufficient. No differences were observed between the iron-deficient and iron-sufficient groups in terms of
the IL-2 concentration without stimulation by PHA. IL-2 production by lymphocytes stimulated with PHA, as well as the stimulation
index (ratio of IL-2 concentration following stimulation by PHA to that of IL-2 concentration without stimulation by PHA)
were significantly lower in iron-deficient children. The reduction in IL-2 production by activated lymphocytes observed in
our study of iron-deficient children may be responsible for impairments in immunity found by other authors, particularly in
cell-mediated immunity. 相似文献
65.
George A. Mason Daniel E. Hernandez Charles B. Nemeroff Jimmie W. Adcock Ossie L. Hatley Arthur J. Prange 《Regulatory peptides》1982,4(5):285-292
Neurotensin (NT) administered intracisternally (i.c.) to adult mice produced a marked hypothermia while prostaglandin E2, administered by the same route, produced hyperthermia. When administered concurrently the effects of the two substances were neutralized. The prostaglandin synthesis inhibitors, indomethacin and acetylsalicylic acid, were injected subcutaneously 30 min prior to i.c. administered NT and/or thyrotropin-releasing hormone (TRH). Both inhibitors failed to potentiate the hypothermia induced by NT or alter its antagonism by TRH in mice kept at 26°C. When mice were kept at 6°C, pretreatment with indomethacin, but not acetylsalicylic acid, potentiated NT-induced hypothermia and prevented its antagonism by TRH. Because indomethacin inhibits synthesis of prostaglandins within the central nervous system (CNS) as well as in peripheral organs while acetylsalicylic acid acts only in the periphery, it appears that NT-induced hypothermia in a cold environment is enhanced by a reduction of prostaglandins in the CNS. 相似文献
66.
67.
From the whole plant of Ajuga chamaepitys two new neo-clerodane diterpenoids, ajugapitin and its dihydro derivative, have been isolated. Their 相似文献
68.
The chemical reaction between (±)-styrene oxide and N-acetylcysteine produces both positional isomers ( and ) as a mixture of diastereoisomers with a preference for the benzylic thioether isomer (2 : 1). Synthesis of the mercapturic acid conjugates from either (+)- or (?)-styrene oxide produces only two of the four possible stereoisomers. The single diastereoisomers of and were separated by high pressure liquid chromatography (HPLC) and identified by 1H- and 13C-nuclear magnetic resonance (NMR). The relative stereochemistry at the benzylic carbon center of the mercapturic acid conjugates was assigned on the basis of the established chemical correlation between optically pure styrene oxide and its precursor mandelic acid, and considerations on the mechanism of ring opening of epoxides by sulfur nucleophiles. The stereochemical definition of the isomers – should prove useful in investigations of the biotransformation of the glutathione (GSH) conjugates of styrene oxide. 相似文献
69.
P.G. Wislocki A.W. Wood R.L. Chang W. Levin H. Yagi O. Hernandez D.M. Jerina A.H. Conney 《Biochemical and biophysical research communications》1976,68(3):1006-1012
(±)-7β,8α-Dihydroxy-9β,10β-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BP 7,8-diol-9,10-epoxide) is a suspected metabolite of benzo[a]pyrene that is highly mutagenic and toxic in several strains of and in cultured Chinese hamster V79 cells. BP 7,8-diol-9,10-epoxide was approximately 5, 10 and 40 times more mutagenic than benzo[a]pyrene 4,5-oxide (BP 4,5-oxide) in strains TA 98 and TA 100 of and in V79 cells, respectively. Both compounds were equally mutagenic to strain TA 1538 and non-mutagenic to strain TA 1535 of . The diol epoxide was toxic to the four bacterial strains at 0.5–2.0 nmole/plate, whereas BP 4,5-oxide was nontoxic at these concentrations. In V79 cells, the diol epoxide was about 60-fold more cytotoxic than BP 4,5-oxide. 相似文献
70.