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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
    A simple technique for transferring excised patches of membrane to different solutions for single channel measurements (1987)
    Springer
    Pflügers Archiv 410 (1987), S. 677-678 
    Details
    ISSN: 1432-2013
    Keywords: patch clamp ; single channels ; excised patches ; solution changes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A technical problem associated with the patch clamp technique has been the changing of solutions bathing the membrane patch. The simple technique described here solves this problem by means of a movable polythene sleeve placed on the shaft of the patch clamp pipette. The sleeve is initially placed so that the tip of the pipette is exposed. A gigaohm seal is formed using standard techniques. The patch is then excised and the sleeve is slipped down a few mm past the end of the tip of the pipette. When the pipette and sleeve is now removed from the solution, a small drop of solution covering the membrane patch is held in place at the end of the sleeve by surface tension. The pipette is then easily transferred to a different solution without passing the membrane patch through the air-water interface. The sleeve is then simply pulled back up the pipette shaft to expose the membrane patch to the new solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00581332
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  • 4
    Electronic Resource
    Electronic Resource
    An analysis of Na+ currents in rat olfactory receptor neurons (1992)
    Springer
    Pflügers Archiv 420 (1992), S. 342-346 
    Details
    ISSN: 1432-2013
    Keywords: Patch-clamp ; Rat ; Olfactory receptor neurons ; Sodium channels
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Na+ currents were observed in acutely-dissociated adult rat olfactory receptor neurons using the whole-cell recording techniques. The threshold for current activation was near −70mV and currents were fully activated by −10 mV (midpoint: −45 mV). Steady-state inactivation was complete at potentials more positive than −70mV and half complete at −110mV (±〈1, n=8). Complete recovery from inactivation required one second at −100 mV (n=7). The addition of 10 μM tetrodotoxin or 1 mM Zn2+ to the external solution was required to completely block the current. The current differs from those in amphibian and cultured neonatal rat olfactory neurons in its unusually negative voltage-dependence and slow recovery. Since mammalian olfactory neurons have very high input resistances, physiological resting potentials cannot usually be measured using whole-cell recording techniques. However, predominantly-capacitatively-coupled spikes activated by depolarisation were frequently observed in cell-attached patches. This indicates that the cells were excitable and implies that they must have had resting potentials more negative than −90 mV in order for this current to underlie the action potential.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00374468
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  • 5
    Electronic Resource
    Electronic Resource
    Ion permeation through single ACh-activated channels in denervated adult toad sartorius skeletal muscle fibres: effect of temperature (1988)
    Springer
    Pflügers Archiv 411 (1988), S. 101-112 
    Details
    ISSN: 1432-2013
    Keywords: Ion permeation ; Temperature ; Channels ; Single channels ; ACh channels ; Patch clamp ; Rate theory ; Electrodiffusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The gigaohm seal technique was used to study the effects of temperature on ion permeation through acetylcholine-activated channels. This was done in cell-attached patches of the extrajunctional membrane of chronicallydenervated, enzyme-treated cells from sartorius muscle of the toadBufo marinus. The predominant extracellular cation in the pipette solution was Na+. Single channel currentvoltage curves were measured at different temperatures and electrodiffusion and three-site-four-barrier rate theory models were used to characterize ion permeation through the channels and determine the effects of temperature on permeation parameters. The fitting of the experimental data to these models suggested the presence of at least three and probably more ion-selective sites within the channel. The most frequently occuring channel type (〉95% of channel openings) had a chord conductance of 25 pS at 11°C and −70 mV and was classified as ‘extrajunctional’. The single channel conductance of this channel had a low temperature-dependence (Q 10≈1.3). The apparent activation enthalpy, Ea, for the conductance between 11°C and 20°C, did not appear to be significantly voltage-sensitive and had a value of about 17±2 kJ·mol−1 at a voltage of −70 mV. The Arrhenius plot of conductance appeared linear between 11 and 20°C at all potentials examined. The data was consistent with a break in the slope of the Arrhenius plot at temperatures between 5 and 11°C at all potentials examined, suggesting a possible phase transition of the membrane lipids. In contrast to the relative permeability, which was not very temperature sensitive, the relative binding constant was significantly affected by temperature. The relative Na/K binding constant sequence was:K 5°C〉 K 20°C〉 K 15°C≫K 11°C. In addition, the decrease in conductance observed at the most depolarized potentials was accentuated as the temperature was increased, suggesting a rate-limiting access step for ions from the intracellular solution into the channel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00581653
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  • 6
    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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  • 7
    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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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    The mechanism of cation permeation in rabbit gallbladder (1971)
    Springer
    The journal of membrane biology 4 (1971), S. 358-394 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The experimental measurements of passive ion permeation in rabbit gallbladder presented in this paper include: single-salt dilution potentials as a function of concentration gradient; comparison of dilution potentials for different alkali chlorides; comparison of biionic potentials for different alkali chlorides; and biionic mixture potentials as a function of cation concentration gradient. Both dilution potentials and biionic potentials yield the permeability sequence K+〉Rb+〉Na+〉Li+〉Cs+, a sequence consistent with simple considerations of ion-site interactions and ion hydration energies. Construction of empirical selectivity isotherms for alkali cation permeation in epithelia shows that permeability ratios are nearer one in the gallbladder and other epithelia than in most other biological membranes, indicating a relatively hydrated permeation route. Evaluation of the results of this and the preceding paper suggests the following: that cations permeate gallbladder epithelium via channels with fixed neutral sites; that the rate-controlling membrane is thick enough that microscopic electroneutrality must be obeyed; that virtually all anion conductance is in a shunt which develops with time after dissection; that apparent permeability changes with solution composition are due to the non-ideal activity factorn being less than 1.0; that effects of pH, Ca++, and ionic strength may involve changes in the anion/cation mobility ratio owing to changes in wall charges or dipoles; and that the permeation route may reside in the tight junctions. A similar mechanism may be applicable to cation permeation in other epithelia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02431979
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  • 10
    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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