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921.
Enhancement of NMDA-mediated responses by cyanide 总被引:2,自引:0,他引:2
Manisha N. Patel Robert W. Peoples George K. W. Yim Gary E. Isom 《Neurochemical research》1994,19(10):1319-1323
The effect of cyanide on NMDA-activated ion current and MK801 binding was studied in cultured rat hippocampal neurons. In microfluorometric analysis using fura-2, removal of extracellular Mg2+ resulted in a five-fold increase in NMDA-induced peak of [Ca2+]i. One mM NaCN enhanced the peak NMDA responses in the presence, but not in the absence of extracellular Mg2+. Cyanide enhanced the immediate rise in [Ca2+]i produced by NMDA, followed over a 1–5 min period by a gradual increase of [Ca2+]i. Similar results were obtained in whole-cell patch clamp recordings from hippocampal neurons. One mM KCN enhanced the NMDA-activated current in the presence, but not in the absence of extracellular Mg2+. This effect was independent of cyanide-mediated metabolic inhibition since the recording pipette contained ATP (2 mM). In binding assays NaCN (1 mM) increased the binding affinity of [3H]MK-801 to rat forebrain membranes in the presence of Mg2+, whereas in the absence of Mg2+, NaCN did not influence binding. These results indicate that cyanide enhances NMDA-mediated Ca2+ influx and inward current by interacting with the Mg2+ block of the NMDA receptor. The effect of cyanide can be explained by an initial interaction with the Mg2+ block of the NMDA receptor/ionophore which appears to be energy-independent, followed by a gradual increase in Ca2+ influx resulting from cellular energy reserve depletion.Abbreviations NMDA
N-Methyl-D-Aspartate
- EAA
excitatory amino acid
- MK-801
(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohept-5,10-imine maleate 相似文献
922.
Some rumen ciliates have endosymbiotic methanogens 总被引:16,自引:0,他引:16
Bland J. Finlay Genoveva Esteban Ken J. Clarke Alan G. Williams T.Martin Embley Robert P. Hirt 《FEMS microbiology letters》1994,117(2):157-161
Abstract Most of the small ciliate protozoa, including Dasytricha ruminantium and Entodinium spp. living in the rumen of sheep, were found to have intracellular bacteria. These bacteria were not present in digestive vacuoles. They showed characteristic coenzyme F420 autofluorescence and they were detected with a rhodamine-labelled Archaea-specific oligonucleotide probe. The measured volume percent of autofluorescing bacteria (1%) was close to the total volume of intracellular bacteria estimated from TEM stereology. Thus it is likely that all of the bacteria living in the cytoplasm of these ciliates were endosymbiotic methanogens, using H2 evolved by the host ciliate to form methane. Intracellular methanogens appear to be much more numerous than those attached to the external cell surface of ciliates. 相似文献
923.
Thomas Pazdernik Robert Cross Stanley Nelson Yumi Kamijo Fred Samson 《Neurochemical research》1994,19(11):1393-1400
A poorly understood marked decrease (circa 50% of control) in local cerebral glucose utilization is caused by sublethal doses of NaCN. The decrease is global, occurring in essentially all brain regions and is entirely reversible within hours, leaving no obvious pathology. This event is not unique to NaCN in so far as a strikingly similar pattern of decreased glucose utilization occus with some other toxins. Nor can it be attributed to a direct action of NaCN since local application by microdialysis to the striatum produces a global depression. These results imply that some widely distributed system or substance is involved. We speculate the existence of a system possibly related to the reticular activating system that senses a fall in energy production and acts globally to make cells quiescent and thus would give some protection from excitotoxic driven damage.Special issue dedicated to Dr. Sidney Ochs. 相似文献
924.
We have previously shown that volatile anesthetics inhibit glutamate-stimulated [3H]MK-801 binding to the ionophore of NMDA receptor complexes in rat brain. In the present study, we examined the influence of enflurane and halothane on NMDA-stimulated45Ca uptake by a microvesicle fraction isolated from rat brain. NMDA stimulated45Ca uptake (30 sec) by rat brain microvesicles by up to 70% with an EC50 of 1.4±0.5 M. The NMDA-stimulated45Ca uptake was inhibited by MK-801 and D-AP-5 with IC50's of 10 M. Enflurane and halothane inhibited45Ca uptake stimulated by 100 M NMDA by as much as 60–80% with IC50's of 0.2–0.3 mM, concentrations achieved during routine clinical use. Basal45Ca uptake measured in the absence of agonist was not affected by the anesthetics. Glycine did not affect the level of NMDA-stimulated45Ca uptake, but markedly reduced the inhibition of uptake caused by enflurane and halothane. Preincubation of microvesicles with NMDA resulted in a desensitization of NMDA-stimulated45Ca uptake, with a t1/2 of 20 sec. Enflurane and halothane diminished both the extent and rate of development of this desensitization, as did glycine. These findings support the idea that volatile anesthetic interference with neurotransmission at NMDA receptor complexes contributes to the development of the anesthetic state. 相似文献
925.
Calvin cycle genes in Nitrobacter vulgaris T3 总被引:1,自引:0,他引:1
Maren Strecker Eva Sickinger Robert S. English Jessup M. Shively 《FEMS microbiology letters》1994,120(1-2):45-50
Abstract The genes encoding the Calvin cycle enzymes of Nitrobacter vulgaris T3 are found as two separate clusters on the chromosome. One cluster contains the genes for the large and small subunits of ribulose-1,5-biphosphate carboxylase/oxygenase (RuBisCO), glyceraldehyde-3-phosphate dehydrogenase, and one encoding a regulatory protein of the LysR family. The other cluster contains the genes for fructose-1,6-/sedoheptulose-1,7-bisphosphatase, phosphoribulokinase, and fructose-1,6-/sedoheptulose-1,7-biphosphate aldolase. With the exception of the LysR-like gene, the genes in each cluster are apparently transcribed in the same direction. The deduced amino acid sequence of both the large and small subunits of RuBisCO are most similar (84–86%) to those of Thiobacillus ferrooxidans and Chromatium vinosum . The deduced sequences of phosphoribulokinase and fructose/sedoheptulose bisphosphatase are 67–73 aand 44–46% similar to those reported for other autotrophic bacteria, respectively. 相似文献
926.
John G. Frazier Harry L. Fierstine Sallie C. Beavers Federico Achaval Hiroyuki Suganuma Robert L. Pitman Yuichiro Yamaguchi Carlos Ma. Prigioni 《Environmental Biology of Fishes》1994,39(1):85-96
Synopsis Billfishes have long been known to impale a great variety of objects, but there are only two brief, obscure records of marine
turtles being speared. Details are presented on these two, as well as on two other confirmed records; data from two additional
unconfirmed records are also presented. In total, three species of marine turtles are known to have been impaled by three
species of billfishes; a fourth species of fish and a fourth species turtle are listed in an unconfirmed case. Records come
from the eastern and western Pacific as well as the eastern Atlantic. Of the four confirmed cases, the turtles survived in
two, and apparently died as an effect of the spearing in the other two. In three confirmed cases only the impaled rostrum
was encountered, and in one confirmed case the entire fish was found, with its rostrum piercing the turtle. There is no obvious
advantage — or clear disadvantage — involved in impaling turtles. It is argued that these attacks are accidental, and the
result of attempts made by the billfish to capture prey that are near the turtle. These spearings indicate that the chelonians
serve as shelters for prey animals on the high seas, and thus, are further evidence of the pelagic existence of marine turtles.
The impalings are evidence of a singular ecological role of the turtles — as live fish aggregation devices. 相似文献
927.
928.
Peter H. Quail Winslow R. Briggs Joanne Chory Roger P. Hangarter Nicholas P. Harberd Richard E. Kendrick Maarten Koornneef Brian Parks Robert A. Sharrock Eberhard Schäfer William F. Thompson Garry C. Whitelam 《Plant Molecular Biology Reporter》1994,12(2):S50-S56
These recommendations for genes encoding phytochromes were developed independently by Quail et al., but are broadly consistent
with the Commission's guidelines. Their original article, kindly provided in advance of publication, appeared as a Letter
to the Editor inPlant Cell (6:468–471, 1994) and is published with permission of the American Society of Plant Physiologists. 相似文献
929.
Blood pressure (BP) and heart rate (HR) data were collected over 24 h with an ambulatory BP monitor to (a) determine the existence of 12-, 24-, and combined 12- and 24-h BP patterns in children as previously noted for adults; (b) provide MESOR (an acronym for midline estimating statistics of rhythm), amplitude, and acrophase data for subgroups of students by race and gender; and (c) determine the influence of HR (as an estimate of activity) on BP and BP patterns for 100 normal, healthy students 9-12 years of age. We found no statistically significant differences between various racial groups or between gender for MESOR, amplitude, acrophase, or degree of sinusoidality of circadian rhythmicity (R2 values) for BP; clinically interesting differences were observed, including lower MESOR BPs in Hispanic males when compared with their female counterparts and slightly higher MESOR BPs in blacks of both genders when compared with whites. In addition, we demonstrated subgroups of students who exhibited specific 24-h and combined 12- and 24-h patterns. Also, 67% of subjects showed stable or nonrhythmic BP patterns, perhaps related to BP sampling intervals. Differences in HR, as a surrogate measure of activity, accounted for 56% of the variation in systolic BP but only 26% in diastolic BP over the 24 h. 相似文献
930.