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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 136 (1993), S. 327-332 
    ISSN: 1432-1424
    Keywords: Guard cells ; Ionic relations ; Nonlinear network ; Membrane voltage ; Oscillations ; Osmosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract In the plasmalemma of plants, the major ion transporters are voltage gated. Hence, they are intrinsically coupled via the membrane voltage. Theoretical predictions and electrophysiological recordings on guard cells demonstrate nonlinear oscillations of a dynamic system which provides longterm osmotic adjustment by switching between periods of net uptake and net release of salt, rather than by a steady-state.
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  • 2
    ISSN: 1432-1424
    Keywords: Key words: KAT1 — Potassium channel — Permeation — Block — Ammonium (NH+4) — Methylammonium (MA)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. The permeation properties of KAT1, an inward rectifying potassium channel from plant cells, were investigated with different ions in the external medium. With either K+, NH+ 4 or methylammonium (MA) in the external solution, the channel, expressed in Xenopus oocytes, appeared permeable to K+ and, to a lesser extent, to NH+ 4 but not to the slightly bigger, methylated analogue of NH+ 4, MA. Substituting NH+ 4 for K+ shifted the voltage dependency of channel activation further negative and hastened activation kinetics. This suggests that channel operation depends on the transported substrate. In mixed solution (50 mm K+, 50 mm MA) MA inhibited K+ current in a voltage-independent manner. The maximum block did not exceed 50% of the K+ current. In contrast, when NH+ 4 was the permeant ion (50 mm NH+ 4, 50 mm MA) MA caused a voltage-dependent, slowly developing open channel block, achieving complete inhibition at very negative voltages. The latter block could be partially overcome by the addition of K+ in the external solution. The data support a model in which ions, after entering the channel pore, compete with different affinities for binding sites on their permeation pathway.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 141 (1994), S. 297-309 
    ISSN: 1432-1424
    Keywords: Action potential ; Chara ; Cell-attached patch clamp techniques ; (Single) Cl− and K+ channel recording
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Patch currents in the cell attached-mode and action potentials (AP) have been recorded simultaneously in internodal cells of Chara corallina. The action potentials are closely correlated with transient patch currents. With pipettes containing either 50 mm CaCl2 or 100 nm KCl plus 1 or 5 mm CaCl2, these transients measured up to 100 to 200 pA per patch at zero mV. Transients had a mean duration (time during which the current was ≥ half maximum peak amplitude) of about 1 sec, a maximum slope for current rising of about 400 pA sec−1 and a maximum rate of about 100 pA sec−1 for current decay, with no obvious effect of external Ca2+ on either of these parameters. In well-resolved recordings of current transients triggered by an action potential (AP), activities of two types of Cl−-conducting channels (15 and 38 pS) have been identified. Since activity of these channels was only observed during action potentials but not upon positive voltage steps, these channels are not directly voltage gated but point to a cytoplasmic gating factor which accumulates during excitation and propagates from excited areas to the patch. A K+-conducting channel (40 pS) could be identified as well during an AP, when 100 mm KCl was in the pipette solution. The activity of this channel relaxed at the end of the APs with a time constant of about 3 sec. Stimulated activity of this channel is understood to cause the repolarization overshoot during the final phase of the action potential, whereas the transient activation of the Cl− channels determines the fast voltage changes of the action potential.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 149 (1996), S. 9-20 
    ISSN: 1432-1424
    Keywords: Key words: Ca2+ block — Coleoptile growth — K+ channel — Patch clamping —Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. Plant growth requires a continuous supply of intracellular solutes in order to drive cell elongation. Ion fluxes through the plasma membrane provide a substantial portion of the required solutes. Here, patch clamp techniques have been used to investigate the electrical properties of the plasma membrane in protoplasts from the rapid growing tip of maize coleoptiles. Inward currents have been measured in the whole cell configuration from protoplasts of the outer epidermis and from the cortex. These currents are essentially mediated by K+ channels with a unitary conductance of about 12 pS. The activity of these channels was stimulated by negative membrane voltage and inhibited by extracellular Ca2+ and/or tetraethylammonium-CI (TEA). The kinetics of voltage- and Ca2+-gating of these channels have been determined experimentally in some detail (steady-state and relaxation kinetics). Various models have been tested for their ability to describe these experimental data in straightforward terms of mass action. As a first approach, the most appropriate model turned out to consist of an active state which can equilibrate with two inactive states via independent first order reactions: a fast inactivation/activation by Ca2+-binding and -release, respectively (rate constants 〉〉103 sec−1) and a slower inactivation/activation by positive/negative voltage, respectively (voltage-dependent rate constants in the range of 103 sec−1). With 10 mm K+ and 1 mm Ca2+ in the external solution, intact coleoptile cells have a membrane voltage (V) of −105 ± 7 mV. At this V, the density and open probability of the inward-rectifying channels is sufficient to mediate K+ uptake required for cell elongation. Extracellular TEA or Ca2+, which inhibit the K+ inward conductance, also inhibit elongation of auxin-depleted coleoptile segments in acidic solution. The comparable effects of Ca2+ and TEA on both processes and the similar Ca2+ concentration required for half maximal inhibition of growth (4.3 mm Ca2+) and for conductance (1.2 mm Ca2+) suggest that K+ uptake through the inward rectifier provides essential amounts of solute for osmotic driven elongation of maize coleoptiles.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 163 (1998), S. 183-191 
    ISSN: 1432-1424
    Keywords: Key words: Action potential —Chara— Patch clamp — Quantal release — Quantal analysis — Cl− channel gating
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. In attached patches on the plasma membrane of nonexcited Chara corallina cells, randomly activating, transient Cl− currents with variable amplitudes were recorded. The peak amplitudes of these currents could be grouped into distinct populations with approximately equidistant mean peak currents. Generally, the mean current of the smallest population measured about half of the distance between the means of subsequent populations. Currents of the smallest population occurred most frequently at all voltages; the frequency of observations decreased with increasing amplitudes of the currents. At all voltages transient currents from different populations were similar in duration with the exception of the smallest currents, which lasted only 0.6 times as long as larger currents. Furthermore, transient currents were most frequent at positive voltages, but once initiated at a positive conditioning pulse they were also observed during subsequent pulses to negative voltages. The results are consistent with the idea that Chara contains Ca2+ stores in the vicinity of the plasma membrane, which are indirectly filled from the external medium. Upon quantal Ca2+ discharge from adjacent stores, a process independent of membrane voltage, the concentration of Ca2+ in the cytoplasm increases transiently. Depending on the number of discharging stores, distinct numbers of Ca2+-stimulated Cl− channels activate, giving rise to the macroscopic excitatory Cl− current in these cells.
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  • 6
    ISSN: 1432-1424
    Keywords: Key words: Capacitance — Exocytosis — Endocytosis — Transient and permanent membrane fusion — Maize coleoptile
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. Exocytosis in protoplasts from Zea mays L. coleoptiles was studied using patch-clamp techniques. Fusion of individual vesicles with the plasma membrane was monitored as a step increase of the membrane capacitance (C m ). Vesicle fusion was observed as (i) An irreversible step increase in C m . (ii) Occasionally, irreversible C m steps were preceded by transient changes in C m , suggesting that the electrical connection between the vesicle with the plasma membrane opens and closes reversibly before full connection is achieved. (iii) Most frequently, however, stepwise transient changes in C m did not lead to an irreversible C m step. Within one patch of membrane capacitance steps due to transient and irreversible fusions were of similar amplitude. This suggests that the exocytosis events do not result from the fusion of vesicles with different sizes but are due to kinetically different states in a fusion process of the same vesicle type. The dwell time histogram of the transient fusion events peaked at about 100 msec. Fusion can be described with a circular three-state model for the fusion process of two fused states and one nonfused state. It predicts that energy input is required to drive the system into a prevailing direction.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    European biophysics journal 29 (2000), S. 515-522 
    ISSN: 1432-1017
    Keywords: Plant injury/stimulation Induced current/magnetic field SQUID magnetometer Injury-induced signal propagation Post-injury distribution of electrical activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract. A superconducting quantum interference device (SQUID) multichannel magnetometer was used to measure the temporal and spatial evolution of the magnetic field accompanying stimulation by burning and/or cutting of Vicia faba plants. These magnetic fields are caused by ionic currents that appear after injury in different parts of the plant. All measured V. faba plants responded to the burning stimulation with detectable quasi-d.c. magnetic signals. In order to measure these signals, a suitable modulation had to be used. The covariance method was applied to analyse the measured data. The results demonstrate a dipolar-like magnetic signal, exponentially decreasing in time, above the cutting type of injury. After the burning stimulation, the magnetically detected activity was concentrated predominantly above the leaves/petioles and less above the stem. Possible mechanisms for this behaviour are suggested. A comparison with previously known electrical measurements of plant injury is given.
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  • 8
    ISSN: 0020-1693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Plant Physiology and Plant Molecular Biology 44 (1993), S. 543-567 
    ISSN: 1040-2519
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    The @Journal of Chemical Thermodynamics 14 (1982), S. 1159-1166 
    ISSN: 0021-9614
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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