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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 110 (1989), S. 127-137 
    ISSN: 1432-1424
    Keywords: membrane ; volume regulation ; permeability cell pH
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary This paper describes computer programs which may be used to identify and analyze cation and anion channels. Weak acids are used to increase intracellular proton concentrations and by so doing to promote the exchange of osmotically active cations with protons. The time course of cation exchange is readily identified from the changes in cell volume which accompany the net changes in osmotically active cations. Weak bases are used to identify and analyze hydroxyl/anion exchange by a comparable strategy. The model was able to produce data that agreed with experimental data in the literatur with an accuracy equal to experimental error. One program, called PROPIONATE, uses the weak acid, propionic acid, to identify cation channels such as the sodium-proton exchanger or the calcium-dependent, potassium channel. A second program, called BASE, is more general because either a weak acid such as propionic acid or a weak base such as ammonia may be used individually or together. When experimental data ara available, the programs may be used to calculate permeability coefficients for ion channels and the capacity of intracellular buffers. The programs may be used also in the design of experiments. Initial values may be assigned to intracellular and extracellular electrolyte and proton concentrations. Values for intracellular buffer capacity and channel permeabilities may be chosen. The program will then generate changes in ions, cell volume, and intracellular pH when either a weak acid, a weak base of combination of the two is added to the external medium.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 134 (1993), S. 225-230 
    ISSN: 1432-1424
    Keywords: Cotransport ; Electrogenic ; Glutamate transport ; Modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract A model for the sodium-dependent accumulation of glutamate by synaptosomes has been presented which fits the data of Wheeler and his coworkers and supports their hypothesis of an electrogenic cotransporter. Since their hypothesis was based on experimental data on the operation of the cotransporter on the outer membrane, the model was expanded to predict events when the cotransporter was operating on both sides of the membrane. The model predicts that the accumulation of glutamate is sensitive to the synaptosomal sodium and emphasizes the importance of the sodium/potassium pump to maintain this value. A model which uses only an electrogenic form of the cotransporter on the external membrane and a neutral form on the inside of the membrane predicts too much or too little accumulation of glutamate at different membrane potentials. A model which uses an electrogenic cotransporter on the external membrane and a concentration-dependent sodium glutamate leak would require a significant increase in the permeability of sodium glutamate when the membrane depolarizes. Only the operation of all four mentioned mechanisms will fit experimental data at two different external sodium concentrations and over the range of membrane potentials measured experimentally.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The permeability of the membranes of different types of leucocytes from several mammalian species to the exosmotic flow of water has been measured at different temperatures. Heats of activation for the process have been calculated. Results indicate that the leucocyte has an unusually high heat of activation for the osmotic movement of water across its outer membrane, ranging between 13 to 18 kcal/mole. Unconstrained water movement usually has values between 3 to 5 kcal/mole. This property characterizes all leucocytes examined to date, regardless of species or type. It is apparent that water is intimately associated with the outer boundary of the cell and that this association is quite sensitive to the structural changes which must occur in response to changes in temperature.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: When exogenous ATP is added to suspensions of TA3 ascites tumor cells suspended in Ca++ and Mg++ free media, a significant increase in cell volume can be measured. This increase is reversible upon addition of Ca++ and/or Mg++ back to the media.The enlargement of these cells is temperature sensitive and specific for ATP; no other nucleotides, EDTA or ouabain were effective. The evidence suggest that this phenomena may be due to an alteration in membrane permeability and that the regulation of membrane permeability is an energy dependent process.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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