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  • Springer  (18)
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  • 1
    Electronic Resource
    Electronic Resource
    Further studies on the charge-related alterations of methotrexate transport in Ehrlich ascites tumor cells by ionic liposomes: Correlation with liposome-cell association (1982)
    Springer
    The journal of membrane biology 66 (1982), S. 87-95 
    Details
    ISSN: 1432-1424
    Keywords: methotrexate ; liposome ; transport ; Ehrlich ; tumor ; cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Interaction of positively (phosphatidylcholine/stearylamine 5∶1) or negatively (phosphatidylcholine/stearic acid 5∶1) charged liposomes with Ehrlich ascites tumor cells for 1–5 min increases or decreases, respectively, the bidirectional fluxes of the folic acid analog, methotrexate. These effects on influx and efflux appear to be symmetrical since the liposomes do not change the intracellular level of methotrexate at the steady state. Influx kinetics show that these alterations result from an increase or decrease in theV max with no change in theK m in . These effects appear to be specific for the methotrexate-tetrahydrofolate carrier system since the transport of other compounds which utilize this carrier, aminopterin, 5-methyltetrahydrofolate, and 5-formyltetrahydrofolate, is affected similarly to methotrexate, whereas, the transport of folic acid, a compound similar in structure and charge but not significantly transported by this carrier is unaffected by liposomes. Once cells are exposed to charged liposomes, the effects on methotrexate transport cannot be reversed by washing the cells free of the extracellular liposomes. If, however, cells are exposed to liposomes of one charge, washed and then exposed to liposomes of the opposite charge, methotrexate influx is reversed to control rates. The effects of charged liposomes on methotrexate influx were not abolished by treating the cells with neuraminidase, metabolic inhibitors or lowering the temperature to 4°C. Studies on the uptake of [14C] liposomes show that these effects are not proportional to the total amount of lipid associated with the cell but result from an initial rapid liposome-cell association that is not dependent on temperature or energy metabolism nor related to cell surface charge.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868485
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  • 2
    Electronic Resource
    Electronic Resource
    Active potassium transport by rabbit descending colon epithelium (1982)
    Springer
    The journal of membrane biology 64 (1982), S. 195-203 
    Details
    ISSN: 1432-1424
    Keywords: epithelium ; potassium ; transport ; membrane potentials ; intracellular K+ activity ; 42K fluxes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Previous studies of rabbit descending colon have disagreed concerning potassium transport across this epithelium. Some authors reported active K+ secretion underin vitro short-circuited conditions, while others suggested that K+ transport occurs by passive diffusion through a highly potassium-selective paracellular route. For this reason, we re-examined potassium fluxes across the colon in the presence of specific and general metabolic inhibitors. In addition, electrochemical driving forces for potassium across the apical and basolateral membranes were measured using conventional and ion-sensitive microelectrodes. Under normal conditions a significant net K+ secretion was observed (J net K =−0.39±0.081 μeq/cm2hr) with42K fluxes, usually reaching steady-state within approximately 50 min following isotope addition. In colons treated with serosal addition of 10−4 m ouabain,J sm K was lowered by nearly 70% andJ ms K was elevated by approximately 50%. Thus a small but significant net absorption was present (J net K =0.12±0.027 μeq/cm2hr). Under control conditions, the net cellular electrochemical driving force for K+ was 17 mV, favoring K+ exit from the cell. Cell potential measurements indicated that potassium remained above equilibrium after ouabain, assuming that passive membrane permeabilities are not altered by this drug. Net K+ fluxes were abolished by low temperature. The results indicate that potassium transport by the colon may occur via transcellular mechanisms and is not solely restricted to a paracellular pathway. These findings are consistent with our previous electrical results which indicated a nonselective paracellular pathway. Thus potassium transport across the colon can be modeled as a paracellular shunt pathway in parallel with pump-leak systems on the apical and basolateral membranes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870886
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of calcium and lanthanum on phosphate efflux from nonmyelinated nerve fibers (1982)
    Springer
    The journal of membrane biology 65 (1982), S. 125-130 
    Details
    ISSN: 1432-1424
    Keywords: nerve fibers ; membrane ; transport ; phosphate ; calcium ; lanthanum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Phosphate efflux was measured as the fractional rate of loss of radioactivity from rabbit vagus loaded with radiophosphate. The effects of changes in extracellular calcium and of lanthanum have been investigated. In Locke solution with normal, 0.9mm, calcium and without phosphate, the fractional rate of loss was 1.62×10−3 min−1 at 120 min after the beginning of the washing period and fell slowly (9% hr−1) during washing from 2 to 6 hr. Addition of calcium to the Locke solution produced a transient increase followed by a reversible maintained increase in phosphate efflux. The latter was 40 and 75% above efflux in normal calcium for 20 and 50mm calcium, respectively. Removal of calcium, with or without addition of EGTA, produced only a transient increase in phosphate efflux, with no subsequent maintained change. Addition of low concentrations of lanthanum produced a reversible inhibition of phosphate efflux. Half-maximal inhibition was at 3.5 μm lanthanum and appeared to be due to binding of lanthanum to more than one, probably two, sites. Measurements of inhibition by lanthanum at different calcium concentrations did not indicate any competition between calcium and lanthanum. It is suggested that at least a part of phosphate efflux depends on internal calcium and that lanthanum acts by preventing release of phosphate from the phosphate transport mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870475
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  • 4
    Electronic Resource
    Electronic Resource
    Amino acid transport in isolated rat hepatocytes (1982)
    Springer
    The journal of membrane biology 69 (1982), S. 1-12 
    Details
    ISSN: 1432-1424
    Keywords: amino acids ; transport ; hepatocytes ; hormones ; adaptive control ; liver
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Improvements in the collagenase perfusion techniques have made isolated rat hepatocytes a popular model in which to study hepatic function. Our knowledge of hepatic amino acid transport has been advanced as a result of this methodology. Translocation across the hepatocyte plasma membrane can, in some instances, represent the rate-limiting step in the overall metabolism of certain amino acids. Furthermore, regulation of amino acid uptake by hepatocytes appears to play a role in diabetes, and perhaps in malignant transformation. Comparisons between normal adult hepatocytes and several hepatoma cell lines show basic differences in amino acids transport. There are at least eight distinct systems in normal hepatocytes for transport of the amino acids. One of these, System A, transports the small neutral amino acids most efficiently and responds to a wide variety of hormones. Systems A and N exhibit enhanced uptake rates after the cells have been maintained in the absence of extracellular amino acids, a phenomenon termed adaptive control. Further studies using isolated hepatocytes will increase our basic understanding of membrane transport processes and their regulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871236
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  • 5
    Electronic Resource
    Electronic Resource
    Study of maturation of membrane transport function in red blood cells by X-ray microanalysis (1982)
    Springer
    The journal of membrane biology 67 (1982), S. 103-111 
    Details
    ISSN: 1432-1424
    Keywords: X-ray microanalysis ; electron probe ; maturation ; transport ; red blood cells ; erythropoiesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Red blood cells of certain species of animals, such as dogs and cats, contain low potassium and high sodium, whereas the erythropoietic stem cells giving rise to these cells are of high potassium type. This paper examines the sequence of membrane transport changes during erythropoiesis by analyzing the K, Na and Fe in single bone marrow cells, reticulocytes and mature red blood cells with X-ray microanalysis. The relationship between K/Na ratios and Fe/(K+Na) ratios were examined by X-ray microanalysis. The K/Na ratios give a measure of the membrane cation transport function. The Fe/(K+Na), which is analogous to hemoglobin concentration, gives an index of maturation stage. The relationships between K/Na and Fe/(K+Na) in the marrow cells of normal adult dog and those of a phenylhydrazine-injected dog with accelerated erythropoiesis show that the modification of cation composition occurs after the initiation of hemoglobin synthesis but before its completion. Similar relationships in the reticulocytes obtained from phenylhydrazine-injected dogs as well as from newborn dogs show a consistent decrease in K/Na with increased Hb, indicating a drastic change in cation composition during the maturation of the reticulocytes. Therefore the modification in membrane transport function must have occurred before or during the formation of reticulocytes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868653
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  • 6
    Electronic Resource
    Electronic Resource
    Thiocyanate transport across fish intestine (Pleuronectes platessa) (1982)
    Springer
    The journal of membrane biology 66 (1982), S. 9-14 
    Details
    ISSN: 1432-1424
    Keywords: thiocyanate ; chloride ; transport ; intestine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary When bathed on both sides with identical chloride-containing salines thein vitro preparation of the plaice intestine maintains a negative (serosa to mucosa) short-circuit current of 107±11 μA/cm2, a transepithelial potential difference of 5.5±0.6 mV (serosa negative), and a mean mucosal membrane potential of −45.4±0.6 mV. Under these conditions the intracellular chloride activity is 32mm. If chloride in the bathing media is partially, or completely substituted by thiocyanate the measured electrical parameters do not change but transepithelial flux determinations show a reduction in chloride fluxes and the presence of a significant thiocyanate flux. The addition of piretanide (10−4 m) reduced the short-circuit current and the mucosa-to-serosa fluxes of chloride and thiocyanate; this inhibition is similar to the effect of piretanide on chloride transport in this tissue. The results indicate that thiocyanate is transported in this tissue via the piretanide-sensitive “chloride” pathway and are compared with the effects of thiocyanate on other tissues reported in the literature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868477
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  • 7
    Electronic Resource
    Electronic Resource
    Entrainment, deposition, and transport of fine-grained sediments in lakes (1982)
    Springer
    Hydrobiologia 91-92 (1982), S. 31-40 
    Details
    ISSN: 1573-5117
    Keywords: sediment ; entrainment ; deposition ; transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Recent work on the settling, diffusion, entrainment, and deposition of fine-grained sediments in fresh water is reviewed and synthesized. Particular attention is given to the dependence of these processes on sediment properties such as particle size. The application of this knowledge to the analysis and numerical modeling of sediment transport is also discussed. Much of the work is concerned with the Great Lakes and, more specifically, with the Western Basin of Lake Erie.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00940094
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  • 8
    Electronic Resource
    Electronic Resource
    Transport of iron and manganese in relation to the shapes of their concentration-depth profiles (1982)
    Springer
    Hydrobiologia 91-92 (1982), S. 463-471 
    Details
    ISSN: 1573-5117
    Keywords: iron ; manganese ; sediments ; water ; transport ; model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A model is presented which describes the transport of iron and manganese in the vicinity of a redox boundary. It is based on input of a particulate component, to form a point source, from which soluble species diffuse along a concentration gradient. The shapes of concentration-depth profiles in marine and freshwater sediments and water columns are reviewed and discussed in terms of the model. Transport, either entirely within a water column or within the sediment, may be simply treated because the rate of vertical transport can be regarded as constant. The discontinuity in the rate of vertical transport which occurs at the sediment-water interface can provide a complicated example of the model, especially when it coincides with the redox boundary. Authigenic mineral formation processes can modify the model, sometimes to such an extent that it becomes invalid. This is particularly true for soluble iron profiles in organically rich marine sediments. Sampling interval is critical to the resultant profile shape and must be relevant to the particular environment, e.g. metres in water columns and millimetres in sediments. The differences in the rates of reduction and oxidation of iron and manganese tend to modify both the position of the profile with respect to the redox-cline and its stage of development in a seasonally anoxic system. It is these factors which determine why most of the iron which reaches a sediment is permanently incorporated whereas manganese is re-released. This mechanism determines the average ratio of iron to manganese in sedimentary rocks. The development of peaked profile shapes in water columns implies that under certain conditions dissolved iron and manganese may be transported from the water column to the pore waters of the sediment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00000044
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  • 9
    Electronic Resource
    Electronic Resource
    Transport of iron and manganese in relation to the shapes of their concentration-depth profiles (1982)
    Springer
    Hydrobiologia 91-92 (1982), S. 463-471 
    Details
    ISSN: 1573-5117
    Keywords: iron ; manganese ; sediments ; water ; transport ; model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A model is presented which describes the transport of iron and manganese in the vicinity of a redox boundary. It is based on input of a particulate component, to form a point source, from which soluble species diffuse along a concentration gradient. The shapes of concentration-depth profiles in marine and freshwater sediments and water columns are reviewed and discussed in terms of the model. Transport, either entirely within a water column or within the sediment, may be simply treated because the rate of vertical transport can be regarded as constant. The discontinuity in the rate of vertical transport which occurs at the sediment-water interface can provide a complicated example of the model, especially when it coincides with the redox boundary. Authigenic mineral formation processes can modify the model, sometimes to such an extent that it becomes invalid. This is particularly true for soluble iron profiles in organically rich marine sediments. Sampling interval is critical to the resultant profile shape and must be relevant to the particular environment, e.g. metres in water columns and millimetres in sediments. The differences in the rates of reduction and oxidation of iron and manganese tend to modify both the position of the profile with respect to the redox-cline and its stage of development in a seasonally anoxic system. It is these factors which determine why most of the iron which reaches a sediment is permanently incorporated whereas manganese is re-released. This mechanism determines the average ratio of iron to manganese in sedimentary rocks. The development of peaked profile shapes in water columns implies that under certain conditions dissolved iron and manganese may be transported from the water column to the pore waters of the sediment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02391960
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  • 10
    Electronic Resource
    Electronic Resource
    An analysis of total phosphorus transport in river systems (1982)
    Springer
    Hydrobiologia 91-92 (1982), S. 241-252 
    Details
    ISSN: 1573-5117
    Keywords: pollution ; rivers ; transport ; calculation ; phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Human activities generate many pollutants from different land uses. These pollutants include nutrients (e.g., phosphorus and nitrogen), toxic substances (e.g., heavy metals and pesticides), and other substances (e.g., chlorides and salts). These materials often enter a river at some upstream point and are transported downstream by the flowing water. Many substances are transported both during storms and during normal river flow and often the major portion of the transport occurs during the storms. This paper considers the quantification of transport primarily during storms. First, the characteristics of storm transport are discussed. Then, a calculation method for estimating the distance of travel for sediment related materials is presented. Third, a technique to estimate the amount of a given chemical passing a point in a stream over a specified period of time is presented. The last part of this paper contains a technique for tracing the movement of substances through a river network. In particular, this procedure yields information as to the source of given pollutants over the entire Storm period.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02391941
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