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91.
LEONOR E. ROVAI AGUSTIN AOKI NELIA M. GEREZ DE BURGOS ANTONCO BLANCO 《The Journal of eukaryotic microbiology》1990,37(4):280-286
Bloodstream Trypanosoma cruzi trypomastigotes isolated from infected mice undergo reduction of motility and structural damages after 5 to 45 min exposure to gossypol at concentrations ranging from 5 to 50 μM. When 1% serum albumin is added to the incubation medium, no alterations of parasites are observed, even with 100 μM gossypol. Intracellular T. cruzi amastigotes in infected Vero cell cultures exposed to 5 μM gossypol for 2 h do not show changes. Incubation with 5 μM gossypol for 48 h produces complete disruption of host cells; however, the amastigotes they contain show only mineor alterations. The observations indicate that, in protein-rich media, gossypol is complexed into associations which have no activity on the different forms of the T. cruzi biological cycle. 相似文献
92.
MARIA APARECIDA VISCONTI ANA MARIA DE LAURO CASTRUCCI 《Pigment cell & melanoma research》1990,3(3):132-140
Norepinephrine (NE) and phenylephrine (Phe) were employed to study the ionic requirements for alpha adrenoceptor activation in the teleost Poecilia reticulata melanophores. As expected the beta adrenoceptor blocker, propranolol, increased the sensitivity of the preparation to NE (5.8 times), and was therefore employed in all the experimental procedures. Neither cocaine (a neuronal uptake blocker) nor dexamethasone (an extraneuronal uptake blocker) enhanced the sensitivity of the preparation to NE, suggesting that these inactivating mechanisms would not play a role in P. reticulata pigmentary system. However, in the absence of calcium, the dose-response curve (DRC) to NE was displaced to the left about 3.5 times, whereas the DRC to Phe was not affected. These results indicate that a neuronal uptake is active, but was not demonstrated by the classical pharmacological tools, probably due to an assymmetric display of the nervous endings. The DRC to NE was rightward displaced (14.1 times) in the presence of the calcium channel blocker Verapamil, whereas the DRC to Phe was not affected. These data suggest that P. reticulata melanophores possess a mixed population of alpha1 and alpha2 adrenoceptors, the activation of the latter eliciting an extracellular calcium influx. In sodium-free saline, the DRC to NE was rightward shifted (6.6 times) and the response to Phe was impaired in such a way that the maximal response was not achieved. The DRC to both NE and Phe were rightward displaced (7.9 and 2.7 times respectively) in the presence of the sodium channel blocker tetrodotoxin (TTX) 10?7M. In potassium-free saline, the melanophore sensitivity to Phe was increased, whereas the responses to NE were not affected, suggesting a differential sensitivity of the two alpha adrenoceptor subtypes to the resulting membrane hyperpolarization. Based on the literature and on our data we propose that P. reticulata melanophores possess a mixed population of alpha1 and alpha2 receptors. The activation of both subtypes of alpha adrenoceptors elicits a Na+ ion influx through TTX-sensitive sodium channels. The stimulation of alpha2 adrenoceptors also requires an extracellular calcium influx, through the opening of slow calcium channels. 相似文献
93.
Separating food and water deprivation in locusts: effects on the patterns of consumption, locomotion and growth 总被引:1,自引:0,他引:1
Abstract. In a factorial experiment, fifth-instar Locusta migratoria (L.) (Orthoptera: Acrididae) were given either dry food (lyophilized grass) and drinking water, food only, water only, or neither food nor water.Food consumption and insect weight were measured daily, and the behaviour of each locust was recorded for 5 h on each of four consecutive days and for 2.5 h on the fifth.Consumption declined progressively in locusts given food only, and those given water only were not observed to drink after the first day of food deprivation.The decline in food consumption on the first day was accounted for by a decrease in the average duration of feeds, which remained constant thereafter.The further decline in consumption over subsequent days was due to a progressive decline in the number of feeds.Although food availability did not slow weight loss relative to locusts given neither food nor water, the availability of water without food did.The proportion of time locomoting increased in all deprivation treatments, but the pattern of change across the five observation days differed markedly between treatments.Locusts given food but no water increased locomotion from 20% of the time budget (the value for controls) to 30% on the first day of deprivation, and by the second day had reached a plateau of approximately 65%.which was maintained until the experiment was terminated on day 5.In contrast, locusts given water but no food approached the 65% level of locomotion on the first day, which was stutistically greater than the 55% observed in those deprived of both food and water.This increase was due both to an increase in the number of locomotion bouts initiated and an increase in the average duration of locomotion bouts.On the second and third days, all deprivation treatments maintained locomotion at around 65%.By day 4, locomotion had decreased to approximately 15% in locusts deprived of both food and water, but not in those deprived of food only or water only.Unlike those given only food, locusts given only water showed a reduction in locomotion of c. 15% on the fifth day. 相似文献
94.
Insulin stimulation of a MEK-dependent but ERK-independent SOS protein kinase. 总被引:5,自引:2,他引:3
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The Ras guanylnucleotide exchange protein SOS undergoes feedback phosphorylation and dissociation from Grb2 following insulin receptor kinase activation of Ras. To determine the serine/threonine kinase(s) responsible for SOS phosphorylation in vivo, we assessed the role of mitogen-activated, extracellular-signal-regulated protein kinase kinase (MEK), extracellular-signal-regulated protein kinase (ERK), and the c-JUN protein kinase (JNK) in this phosphorylation event. Expression of a dominant-interfering MEK mutant, in which lysine 97 was replaced with arginine (MEK/K97R), resulted in an inhibition of insulin-stimulated SOS and ERK phosphorylation, whereas expression of a constitutively active MEK mutant, in which serines 218 and 222 were replaced with glutamic acid (MEK/EE), induced basal phosphorylation of both SOS and ERK. Although expression of the mitogen-activated protein kinase-specific phosphatase (MKP-1) completely inhibited the insulin stimulation of ERK activity both in vitro and in vivo, SOS phosphorylation and the dissociation of the Grb2-SOS complex were unaffected. In addition, insulin did not activate the related protein kinase JNK, demonstrating the specificity of insulin for the ERK pathway. The insulin-stimulated and MKP-1-insensitive SOS-phosphorylating activity was reconstituted in whole-cell extracts and did not bind to a MonoQ anion-exchange column. In contrast, ERK1/2 protein was retained by the MonoQ column, eluted with approximately 200 mM NaCl, and was MKP-1 sensitive. Although MEK also does not bind to MonoQ, immunodepletion analysis demonstrated that MEK is not the insulin-stimulated SOS-phosphorylating activity. Together, these data demonstrate that at least one of the kinases responsible for SOS phosphorylation and functional dissociation of the Grb2-SOS complex is an ERK-independent but MEK-dependent insulin-stimulated protein kinase. 相似文献
95.
Surveys of the principal yellowing viruses of sugar beet, beet yellows virus (BYV) and beet mild yellowing virus (BMYV) in Spain were carried out from 1990–1993. Beet yellowing viruses were detected in all provinces, although the mean percentages of plants infected with BYV and BMYV were practically zero in the southern zone. Within the northern zone high variations from one province to another could be observed. The mean percentages of plants infected with BYV were higher in the Ebro Valley than in the Duero Valley. Areas infected with BYV were very restricted, while BMYV could be found to a variable extent all over Spain, although the infection levels were lower. The incidence and distribution of these viruses in the Spanish sugar beet crop makes the study and application of control measures for beet yellowing viruses necessary. 相似文献
96.
97.
REYNALDO LUIZ VICTORIA FERNANDO FERNANDES† LUIZ ANTONIO MARTINELLI MARISA DE CÁSSIA PICCOLO PLINIO BARBOSA DE CAMARGO SUSAN TRUMBORE‡ 《Global Change Biology》1995,1(3):165-171
Measurements of the organic carbon inventory, its stable isotopic composition and radiocarbon content were used to deduce vegetation history from two soil profiles in arboreal and grassy savanna ecotones in the Brazilian Pantanal. The Pantanal is a large floodplain area with grass-dominated lowlands subject to seasonal flooding, and arboreal savanna uplands which are only rarely flooded. Organic carbon inventories were lower in the grassy savanna site than in the upland arboreal savanna site, with carbon decreasing exponentially with depth from the surface in both profiles. Changes in 13C of soil organic matter (SOM) with depth differed markedly between the two sites. Differences in surface SOM 13C values reflect the change from C3 to C4 plants between the sites, as confirmed by measurements of 13C of vegetation and the soil surface along a transect between the upland closed-canopy forest and lowland grassy savanna. Changes of 13C in SOM with depth at both sites are larger than the 3–4 per mil increases expected from fractionation associated with organic matter decomposition. We interpret these as recording past changes in the relative abundance of C3 and C4 plants at these sites. Mass balances with 14C and 13C suggest that past vegetational changes from C3 to C4 plants in the grassy savanna, and in the deeper part of the arboreal savanna, occurred between 4600 and 11 400 BP, when major climatic changes were also observed in several places of the South American Continent. The change from C4 to C3, observed only in the upper part of the arboreal savanna, was much more recent (1400 BP), and was probably caused by a local change in the flooding regime. 相似文献
98.
99.
SIMONE LUIZ RICARDO LOPES DE; MORACCHIOLI NICOLETTA 《Journal of Molluscan Studies》1994,60(4):445-459
Potamolithus karsticus n. sp. and Potamolithus troglo-bius n.sp., two Brazilian aquatic cavesnails (Gastropoda: Hydrobiidae),are described. P. troglobius is blind and depigmented, and isthe first stygobiontic snail to be described from Brazil Additionally, specimens of Potamolithus ribeirensis Pilsbry,1911 were collected near the type locality for comparison withthe new cave species (Received 2 December 1993; accepted 20 June 1994) 相似文献
100.