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  • 1
    Electronic Resource
    Electronic Resource
    Slow conductance changes due to potassium depletion in the transverse tubules of frog muscle fibers during hyperpolarizing pulses (1973)
    Springer
    The journal of membrane biology 14 (1973), S. 243-292 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary When hyperpolarizing currents are applied between the inside and outside of a muscle fiber it is known that there is a slow transient decrease (300- to 600-msec time constant) in the measured fiber conductance sometimes referred to as “creep” which is maximal in K2SO4 Ringer's solutions and which disappears on disruption of the transverse tubular system. An approximate mathematical analysis of the situation indicates that these large, slow conductance changes are to be expected from changes in the K+ concentration in the tubular system and are due to differences in transport numbers between the walls and lumen of the tubules. Experiments using small constant-voltage and constant-current pulses (membrane p. d. changes ≲20 to 30 mV) on the same fibers followed by an approximate mathematical and more exact computed numerical analysis using the measured fiber parameters and published values of tubular system geometry factors showed close agreement between the conductance creep predicted and that observed, thus dispensing with the need for postulated changes in individual membrane conductances at least during small voltage pulses. It is further suggested that an examination of creep with constant-voltage and constant-current pulses may provide a useful tool for monitoring changes in tubular system parameters, such as those occurring during its disruption by presoaking the fibers in glycerol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868081
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  • 2
    Electronic Resource
    Electronic Resource
    GLYCINE RECEPTORS: WHAT GETS IN AND WHY? (1999)
    Melbourne, Australia : Blackwell Science Pty
    Clinical and experimental pharmacology and physiology 26 (1999), S. 0 
    Details
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 1. The glycine receptor channel (GlyR), a member of the ligand-gated ion channel superfamily, shares many similar permeation properties with the GABAA receptor channel.2. The GlyR is anion permeable, with PK/PCl 〈 0.05, has a 5–6 Å minimum pore diameter and a permeation selectivity sequence dominated by hydration energies.3. The channels, which display multiple subconductance states, can be multiply occupied.4. Two positive arginine rings at the ends of the pore region may contribute to the anion selectivity of the GlyR.5. Mutation of the extracellular charged arginine ring can impair channel function by decreasing the sensitivity of glycine activation, reducing channel conductance, shifting the normal multi-subconductance states to lower values and by decoupling the link between ligand binding and channel gating.6. These and other site-directed mutagenesis studies of recombinant GlyR, together with studies of native GlyR, are providing further insights into what controls gating and ion permeation and selectivity through this channel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1440-1681.1999.03149.x
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  • 3
    Electronic Resource
    Electronic Resource
    Volume flows and pressure changes during an action potential in cells ofChara australis (1970)
    Springer
    The journal of membrane biology 3 (1970), S. 313-334 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Methods have been used for monitoring either volume flows or pressure changes, simultaneously with membrane potentials, in giant algal cells ofChara australis during an action potential. The volume flows were measured from the movement of a mercury bead in a capillary tube recorded by a photo-transducer. The pressure changes were measured by monitoring the deflection of a thin wedge, resting transversely across a cell, and using the same photo-transducer, the deflection of the wedge being directly related to the cell's turgor pressure. The average maximum rate of volume flow per unit area during an action potential was 0.88±0.11 nliter·sec−1·cm−2 in the direction of an outflow from the cell (total volume outflow being about 3 nliter·cm−2 per action potential). Similarly, the maximum rate of change of pressure was 19.6±3.8×10−3 atm·sec−1 (peak change being 19.3±2.9×10−3 atm equivalent to 14.7±2.2 mm Hg). The volume flow and pressure changes followed the vacuolar potential quite closely, the peak rate of volume flow lagging behind the peak of the action potential by 0.17±0.08 sec and the peak rate of pressure change leading it by 0.09±0.07 sec.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868022
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  • 4
    Electronic Resource
    Electronic Resource
    Volume flows and pressure changes during an action potential in cells ofChara australis (1970)
    Springer
    The journal of membrane biology 3 (1970), S. 335-371 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary It has been suggested that electro-kinetic coupling may be involved in the mechanism of the action potential and that there should therefore be both consequent volume flows and pressure changes associated with such excitation. In a previous paper, such measurements were reported in cells ofChara australis, from which it is also known that during excitation there is an increase in KCl permeability and an efflux of KCl. In this paper, a number of theoretical analyses have been considered and developed pertaining to such measurements and the time-dependent relationships between apparent measured volume flows, true volume flows and turgor pressure changes in cells in various experimental situations. Such volume flows are quantitatively explained primarily from the frictional coupling of water by both K+ and Cl− ions and to a lesser extent by the local osmotic flow owing to KCl enhancement at the wall-membrane interface of the cell. The measured pressure changes of 12×10−3 to 28×10−3 atm during excitation are also correctly predicted as the result of such a volume outflow from the cell which behaves as a hydraulically leaky elastic cylinder and thereby drops in pressure. These conclusions then indicate that the volume flows and pressure changes measured are the incidental consequences of a change in membrane permeability and do not necessarily imply any electro-kinetic mechanism for the action potential itself.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868023
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  • 5
    Electronic Resource
    Electronic Resource
    Transport number effects in the transverse tubular system and their implications for low frequency impedance measurement of capacitance of skeletal muscle fibers (1977)
    Springer
    The journal of membrane biology 34 (1977), S. 383-408 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary It has been shown in an earlier paper that the slow transient decrease in conductance, somtimes referred to as “creep”, obtained with small-to-medium hyperpolarizing current or voltage pulses is due to K+ transport number differences across the walls of the transverse tubular system. Using the same basic numerical analysis and the parameters already obtained experimentally in the previous paper for frog skeletal muscle in a sulphate Ringer's solution, this paper predicts the equivalent membrane capacitance and dynamic resistance due to transport number effects for very low amplitude and low frequency sinusoidal currents from the phase lag of the voltage response behind the current. Such sinusoidal currentper se give rise to an equivalent capacitance which increased from less than 1μF·cm−2 at 10 Hz to about 16μF·cm−2 at 0.01 Hz and to an equivalent dynamic membrane resistance which increases from its instantaneous slope resistance value of 11.7kωcm2 at 10 Hz to about 16kωcm2 at 0.01 Hz. Similar small sinusoidal components of current superimposed on depolarizing and hyperpolarizing pulses (25–45 mV) give rise to even greater “capacitances” at low frequencies (e.g., 24–28μF·cm−2 at 0.01 Hz). The response due to large sinusoidal currents was also investigated. These transport number effects help to explain the small discrepancies obtained by some workers between experimental and predicted values of skeletal muscle fiber impedances measured in the 1–10 Hz range and would seem to be critical for the interpretation of any skeletal muscle fiber impedance studies done at frequencies less than 1 Hz.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870310
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  • 6
    Electronic Resource
    Electronic Resource
    Cation permeation at the amphibian motor end-plate (1979)
    Springer
    The journal of membrane biology 45 (1979), S. 245-276 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Measurements of acetylcholine-induced single-channel conductance and null potentials at the amphibian motor end-plate in solutions containing Na, K, Li and Cs ions (Gage & Van Helden, 1979;J. Physiol. (London) (in press) were analyzed in terms of three models. Two of these models, the “neutral” site channel model and the “charged” site channel model were developed to cater for three cations. Both were shown to be able to explain the dependence of single-channel conductance on membrane potential and gave the following sequences of equilibrium constants and mobilities.K Li/K Na/K K/K Cs=7∶1.7∶1∶0.9 andu Cs/u K/u Na/u Li=1.4∶1∶0.58∶0.13 at 8 °C. Similar sequences were obtained at 20 °C. Although the neutral model fitted the data for relative conductances in Li-, Cs-and Na-solutions slightly better than the charged model, experiments done in normal [NaCl] and [NaCl]/2 solutions could only be fitted by the neutral model. In contrast, the third model, the Constant Field Equation, was unable to fit the conductance data in any of the above situations. The data available suggests that permeation is through “long” neutral channels, lined with high field-strength negative polar groups and including one or possibly more high resistance barriers for anions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869288
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  • 7
    Electronic Resource
    Electronic Resource
    A theory of ion permeation through membranes with fixed neutral sites (1971)
    Springer
    The journal of membrane biology 4 (1971), S. 295-330 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Some model membranes and biological membranes behave as if ion permeation were controlled by fixed neutral sites, i.e., by groups that are polar but lack net charge. By solving the boundary conditions and Nernst-Planck flux equations, this paper derives the expected properties of four types of membranes with fixed neutral sites: model 1, a membrane thick enough that microscopic electroneutrality is obeyed; model 2, same as model 1 but with a free-solution shunt in parallel; model 3, a membrane thin enough that microscopic electroneutrality is violated; and model 4, same as model 3 but with a free-solution shunt in parallel. The conductance-concentration relation and the current-voltage relation in symmetrical solutions are approximately linear for all four models. Partial ionic conductances are independent of each other for a thin membrane but not for a thick membrane. Sets of permeability ratios derived from conductances, dilution potentials, or biionic potentials agree with each other in a thin membrane but not in a thick membrane. The current-voltage relation in asymmetrical single-salt solutions is linear for a thick membrane but nonlinear for a thin membrane. Examples of potential and concentration profiles in a thin membrane are calculated to illustrate the meaning of space charge and the electroneutrality condition. The experimentally determined properties (by A. Cass, A. Finkelstein & V. Krespi) of thin lipid membranes containing “pores” of the anion-selective antibiotic nystatin are in reasonable agreement with model 3. Tests are suggested for deciding if a membrane of unknown structure has neutral sites, whether it is thick or thin, and whether the sites are fixed or mobile.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02431977
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  • 8
    Electronic Resource
    Electronic Resource
    The mechanism of cation permeation in rabbit gallbladder (1971)
    Springer
    The journal of membrane biology 4 (1971), S. 331-357 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The questions underlying ion permeation mechanisms, the types of experiments available to answer these questions, and the properties of some likely permeation models are examined, as background to experiments designed to characterize the mechanism of alkali cation permeation across rabbit gallbladder epithelium. Conductance is found to increase linearly with bathing-solution salt concentrations up to at least 400mm. In symmetrical solutions of single alkali chloride salts, the conductance sequence is K+〉Rb+〉Na+〉Cs+∼Li+. The current-voltage relation is linear in symmetrical solutions and in the presence of a single-salt concentration gradient up to at least 800 mV. The anion/cation permeability ratio shows little change with concentration up to at least 300mm. Ca++ reduces alkali chloride single-salt dilution potentials, the magnitude of the effect being interpreted as an inverse measure of cation equilibrium constants. The equilibrium-constant sequence deduced on this basis is K+〉Rb+〉Na+∼Cs+∼Li+. These results suggest (1) that the mechanism of cation permeation in the gallbladder is not the same as that in a macroscopic ion-exchange membrane; (2) that cation mobility ratios are closer to one than are equilibrium-constant ratios; (3) that the rate-limiting step for cation permeation is in the membrane interior rather than at the membrane-solution interface; and (4) that the rate-controlling membrane is one which is sufficiently thick that it obeys microscopic electroneutrality.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02431978
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  • 9
    Electronic Resource
    Electronic Resource
    Slow potential changes due to transport number effects in cells with unstirred membrane invaginations or dendrites (1984)
    Springer
    The journal of membrane biology 82 (1984), S. 221-239 
    Details
    ISSN: 1432-1424
    Keywords: transport number effects ; membrane invaginations ; dendrites ; restricted diffusion space ; slow potential changes ; slow conductance changes ; neurones ; solute polarization ; membrane infoldings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Many neurones are extremely invaginated and possess branching processes, axons and dendrites. In general, they are surrounded by a restricted diffusion space. Many of these cells exhibit large, slow potential changes during the passage of current across their membranes. Whenever currents cross membranes separating aqueous solutions, differences in transport numbers of the major permeant ions give rise to local concentration changes of these ions adjacent to the membranes, which will result in various electrical and osmotic effects. These transport number effects are expected to be enhanced by the presence of membrane invaginations. Dendrites are equivalent to reversed invaginations and there should be significant changes in concentrations of permeant ions within them. In general, the effects of such changes on the electrical response of a cell will be greater when the concentration of a major permeant ion is low. The effects have been modelled in terms of two nondimensional parameters: the invagination transport number parameter β and the relative area occupied by the invaginations δA. If these two parameters are known, the magnitudes and time course of the slow potential changes can immediately be estimated and the time course converted to real time, if the length of the invaginations (l) and ionic diffusion coefficient (D) within them are also known. Both analytical and numerical solutions have been given and predictions compared. It is shown that in the case of large currents and potentials the analytical solution predictions will underestimate the magnitudes and rates of onset of the voltage responses. The relative magnitude of the transport number effect within the invaginations (or dendrites) and other transport number contributions to slow potential changes have also been assessed and order-of-magnitude values of these are estimated for some biological data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871632
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  • 10
    Electronic Resource
    Electronic Resource
    Slow potential changes in mammalian muscle fibers during prolonged hyperpolarization: Transport number effects and chloride depletion (1984)
    Springer
    The journal of membrane biology 78 (1984), S. 235-248 
    Details
    ISSN: 1432-1424
    Keywords: transport number effects ; chloride depletion ; slow potential changes ; slow conductance changes ; creep ; mammalian muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Mammalian skeletal muscle fibers exhibit large slow changes in membrane potential when hyperpolarized in standard chloride solutions. These large slow potential changes are radically reduced in low chloride solutions, where the faster and smaller potential change (“creep”), usually observed in amphibian fibers, becomes apparent. The slow potential change during a hyperpolarizing current pulse leads to an increase in apparent resistance of up to nine times the instantaneous value and takes minutes to reach a steady value. It then takes a similar time to decay very slowly back to the resting membrane potential after the current pulse. The halftime for the slow potential change was found to be inversely proportional to the current magnitude. From measurements of immediate postpulse membrane potentials, assuming constant ionic permeabilities, the internal chloride concentration was calculated to decrease exponentially towards a steady value (e.g., for one fiber from 12.3 to 6.6mm after a 330-sec pulse). The time course and magnitude of the concentration change were predicted from chloride transport number differences, and the known and measured properties of the fibers, and were found to agree very well with the values obtained from experimental measurements. In addition, the shapes of theV 2-V 1 responses, measured in the three-electrode current clamp set-up with either potassium chloride or potassium citrate current electrodes, were as predicted by transport number chloride depletion effects and were at variance with the predictions of a permeability change mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01925971
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