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51.
Summary Sodium-calcium exchange has been suggested to play a pivotal role in the regulation of cytosolic free calcium (Ca
f
) by epithelial cells. Using isolated epithelial cells from the toad urinary bladder, Ca
f
has been measured using the intracellular Casensitive fluorescent dyes Fura 2 and Quin. 2. Dye loading did not alter cell viability as assessed by measurements of ATP and ADP content or cell oxygen consumption. When basal Ca
f
was examined over a wide range of cell dye content (from 0.04 to 180 nmol dye/mg protein) an inverse relationship was observed. At low dye content, Ca
f
was 300–380 nM and, as dye content was increased, Ca
f
progressively fell to 60 nM. Using low dye content cells, in which minimal alteration in Ca steady state would be expected, the role for plasma membrane Na–Ca exchange was examined using either medium sodium substitution or ouabain. While medium sodium substitution increased Ca
f
, prolonged treatment with ouabain had no effect on Ca
f
despite a clear increase in cell sodium content. The lack of effect of ouabain suggests that Na–Ca exchange-mediated Ca efflux plays a minimal role in the regulation of basal Ca
f
. However, exchange-mediated Ca efflux may play a role in Ca
f
regulation when cytosolic calcium is elevated. 相似文献
52.
Grant N. Pierce 《Molecular and cellular biochemistry》1987,78(1):89-94
Na+-H+ exchange and passive Na+ flux were investigated in cardiac sarcolemmal vesicles as a function of changing the ionic composition of the reaction media. The inclusion of EGTA in the reaction medium resulted in a potent stumulation of Na+ uptake by Na+-H+ exchange. It was found that millimolar concentrations of Mg2+ and Li+ were capable of inhibiting Na+-H+ exchange by 80%. One mechanism by which these ions may inhibit intravesicular Na+ accumulation by Na+-H+ exchange is via an increase in Na+ efflux. An examination of Na+ efflux kinetics from vesicles pre-loaded with Na+ revealed that Na+, Ca2+, Mg2+ and Li+ could stimulate Na+ efflux. Na+-H+ exchange was potently inhibited by an organic divalent cation, dimenthonium, which screens membrane surface charge. This would suggest that Na+-H+ exchange occurs in the diffuse double layer region of cardiac sarcolemma and this phenomenon is distinctly different from other Na+ transport processes. The results in this study indicate that in addition to a stimulation of Na+ efflux, the inhibitory effects of Mg2+, Ca2+ and Li+ on Na+-H+ exchange may also involve a charge dependent screening of Na+ interactions with the membrane. 相似文献
53.
Voltage-dependent depolarization of bacterial membranes and artificial lipid bilayers by the peptide antibiotic nisin 总被引:24,自引:0,他引:24
The peptide antibiotic nisin is shown to disrupt valinomycin-induced potassium diffusion potentials imposed on intact cells of Staphylococcus cohnii 22. Membrane depolarization occurred rapidly at high diffusion potentials while at low potentials nisin-induced depolarization was slower suggesting that nisin requires a membrane potential for activity. This assumption was proven in experiments with planar lipid bilayers (black lipid membranes). Macroscopic conductivity measurements indicated a voltage-dependent action of nisin. The potential must have a trans-negative orientation with respect to the addition of nisin (added to the cis-side) and a sufficient magnitude (ca. -100 mV). With intact cells the threshold potential was lower (-50 to -80 mV at pH 7.5 and below -50 mV at pH 5.5). Single channel recordings resolved transient multistate pores, strongly resembling those introduced by melittin into artificial bilayers. The pores had diameters in the range of 0.2–1 nm, and lifetimes of few to several hundred milliseconds. The results indicate that nisin has to be regarded as a membrane-depolarizing agent which acts in a voltage-dependent fashion.Abbreviations BLM
Black lipid membranes
- CCCP
carbonyl cyanide m-chlorophenylhydrazone
- DOPC
dioleoyl phosphatidylcholine
- PS
phosphatidylserine
- TPP+
tetraphenylphosphonium cation 相似文献
54.
Kyriacos Athanasiou Iordanis Arzimanoglou Colette Piccoli Hiroshi Yamasaki 《Cell biology and toxicology》1987,3(3):251-261
Airborne particulates were collected over a period of twelve months by the use of Hi-Vol samplers in the basin of Athens, Greece. N-Hexane extracts were tested in a battery ofin vitro tests for their ability to induce mutation in bacteria as well as mutation, sister chromatid exchange and morphological transformation in cultured mammalian cells. Positive results were found for mutagenicity withSalmonella strain TA98 in the Ames assay, for sister chromatid exchange induction in CHO cells and for transformation in BALB/c 3T3 cells in culture. They also showed weak non-doserelated induction of ouabain resistance in BALB/c 3T3 cells. The contribution of oxidizing and nitrating agents found in the Athens atmosphere, together with sunlight UV irradiation in the formation of direct acting mutagens and potential carcinogens from ambient polycyclic aromatic hydrocarbons, is suggested.Abbreviations FCS
fetal calf serum
- FPG
fluorescent-plus-Giemsa technique
- ouaR
ouabain resistant
- PAH
polycyclic aromatic hydrocarbon
- SCE
sister chromatid exchange
- TSP
total suspended particulate 相似文献
55.
Summary Using Laser Doppler Anemometry we measured current velocities in the median plane around dead lotic macroinvertebrates in a flume which reproduced natural near bottom hydraulics. We investigated specimens of the gastropods Ancylus, Acroloxus, and Potamopyrgus, the amphipod Gammarus, and the larval caddisflies Anabolia, Micrasema, and Silo of various size, various alignment to the flow or which were otherwise manipulated in order to clarify certain questions of adaptation of shape or case building style to flow, or the effects of flow on field distribution patterns. The steepest velocity gradients close to the animals were found near areas of their bodies protruding furthest into the flow. In such regions the rates of potential diffusive exchange processes, the potential corrasion (abrasion through suspended solids), and, for larger specimens, the lift forces (directed towards the water surface) must be highest. Posterior of these areas growing boundary layers formed above those species whose upper contour was approximately parallel to the upstream-downstream direction of the flow. All specimens removed momentum from the flow and thus experience a drag force (directed downstream). From the complete data set we derived the following general conclusions about the physical effects of potential morphological adaptations, taking into consideration diffusion through boundary layers, corrasion, lift forces, friction and pressure drag forces: The physical significance of these five factors generally depends on the Reynolds number of an animal and is largely affected by flow separation, which was significantly related to the ratio of body length to height and the slope of the posterior contour. A simultaneous effective morphological adaptation to all five factors is physically impossible and, in addition, would have to change from life at low (e.g. a young, small specimen of a species) to life at high (e.g. a fully grown specimen of the same species) Reynolds number. 相似文献
56.
Changes in gas exchange characteristics and water use efficiency of mangroves in response to salinity and vapour pressure deficit 总被引:12,自引:0,他引:12
Summary Measurements were made of the photosynthetic gas exchange properties and water use efficiency of 19 species of mangrove in 9 estuaries with different salinity and climatic regimes in north eastern Australia and Papua New Guinea. Stomatal conductance and CO2 assimilation rates differed significantly between species at the same locality, with the salt-secreting species, Avicennia marina, consistently having the highest CO2 assimilation rates and stomatal conductances. Proportional changes in stomatal conductance and CO2 assimilation rate resulted in constant and similar intercellular CO2 concentrations for leaves exposed to photon flux densities above 800 mol·m-2·s-1 in all species at a particular locality. In consequence, all species at the same locality had similar water use efficiencies. There were, however, significant differences in gas exchange properties between different localities. Stomatal conductance and CO2 assimilation rate both decreased with increasing salinity and with increasing leaf to air vapour pressure deficit (VPD). Furthermore, the slope of the relationship between assimilation rate and stomatal conductance increased, while intercellular CO2 concentration decreased, with increasing salinity and with decreasing ambient relative humidity. It is concluded from these results that the water use efficiency of mangroves increases with increasing environmental stress, in this case aridity, thereby maximising photosynthetic carbon fixation while minimising water loss.Contribution No. 459 from the Australian Institute of Marine Science 相似文献
57.
G. Goldstein F. Rada L. Sternberg J. L. Burguera M. Burguera A. Orozco M. Montilla O. Zabala A. Azocar M. J. Canales A. Celis 《Oecologia》1989,78(2):176-183
Summary The gas exchange and water relations of the hemiparasite Pthirusa maritima and two its mangrove host species, Conocarpus erectus and Coccoloba uvifera, were studied in an intertidal zone of the Venezuelan coast. Carbon uptake and transpiration, leaf osmotic and total water potential, as well as nutrient content in the xylem sap and leaves of mistletoes and hosts were followed through the dry and wet season. In addition, carbon isotope ratios of leaf tissue were measured to further evaluate water use efficiency. Under similar light and humidity conditions, mistletoes had higher transpiration rates, lower leaf water potentials, and lower water use efficiencies than their hosts. Potassium content was much higher in mistletoes than in host leaves, but mineral nutrient content in the xylem sap of mistletoes was relatively low. The resistance of the liquid pathway from the soil to the leaf surface of mistletoes was larger than the total liquid flow resistance of host plants. Differences in the daily cycles of osmotic potential of the xylem sap also indicate the existence of a high resistance pathway along the vascular connection between the parasite pathway along the vascular connection between the parasite and its host. P. maritima mistletoes adjust to the different physiological characteristics of the host species which it parasitizes, thus ensuring an adequate water and carbon balance. 相似文献
58.
C. Bevan R. K. H. Kinne R. E. Shetlar E. Kinne-Saffran 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1989,159(3):339-347
Summary A membrane fraction, rich in brush border membranes, was prepared from renal proximal tubules of the spiny dogfish,Squalus acanthias, and the sodium-proton exchange mechanism in these membrane vesicles was investigated by both a rapid filtration technique and the fluorescence quenching of acridine organe.22Na+ uptake was stimulated by an outwardly directed H+ gradient, and was inhibited by amiloride at a single inhibitory site with an apparentK
i
of approximately 1.7×10–5
M. In the presence of an H
i
+
>H
o
+
gradient, the
of the Na+/H+ exchanger were 9.7±0.8 mM and 48.0±12.0 nmol·mg protein–1·min–1, respectively. The uptake of Na+ was electroneutral in the presence of a H+ gradient, indicating a stoichiometry of 1. In the fluorescence studies, quenching of acridine orange occurred in the presence of an outwardly directed Na+ gradient which was inhibited by amiloride. Thus, an electroneutral Na+/H+ exchanger with properties similar to those found in the mammalian kidney is also present in the spiny dogfish and may contribute to the urinary acidification of this marine animal. 相似文献
59.
The viability ofMycobacterium leprae, maintained within 33B Schwannoma cells, was estimated in terms of incorporation of [14C] acetate into its specific phenolic glycolipid-1. This measure of viability was correlated with two other assays,viz., fluorescein diacetate/ethidium bromide staining and mouse footpad growth. Observation of a 2-fold increase in the number
of intracellularMycobacterium leprae over an experimental period of 12 days also corroborated this contention. Furthermore, on addition of anti-leprosy drugs
to these intracellularMycobacterium leprae there was significant decrease in phenolic glycolipid-1 synthesis indicative of loss of viability of the organisms. This
study also established the importance of the host cell for active bacillary metabolism, asMycobacterium leprae maintained in cell-free conditions showed no incorporation into phenolic glycolipid-1. Moreover, compromising the host’s
protein synthesis capacity with cycloheximide, also led to reduction in bacillary metabolism. As this system measures the
metabolic synthesis of a uniqueMycobacterium leprae component, it would be useful for development and screening of compounds acting against specific bacillary targets. 相似文献
60.
Cholesterol binding reserve of hyperlipemic rat serum lipoproteins in chronic ethanol administration
Chronic administration of ethanol in rats caused the reduction of serum cholesterol binding reserve. The very low density
and high density lipoproteins, main serum cholesterol binding reserves, were slightly increased with corresponding increases
in their lipid and protein components during initial stage of alcohol consumption. However, these capacities get deminished
during reversal of hyperlipemia induced by prolonged action of ethanol. This situation may be an early indicator for the initiation
of hepatic damage and a variety of secondary effects of ethanol. 相似文献