Slow kinetics of a potassium channel inAcetabularia

Bertl, Adam; Klieber, Hans-Georg; Gradmann, Dietrich

doi:10.1007/bf01870452

Cited by 31 publications

(27 citation statements)

References 10 publications

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“…Acetabularia, data fitted a three-state model with two closed states and four rate constants, in which equilibration between the two closed states was potential-dependent (Bertl et al, 1988). In Chara, data fitted a model with at least seven distinct closed states and one open state (Laver & Walker, 1987).…”

Section: Gating and Kineticsmentioning

confidence: 94%

Tansley Review No. 21 Plant ion channels: whole‐cell and single channel studies

Tester¹

1990

New Phytologist

301

166

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SUMMARY Ion channels are proteins which catalyse rapid, passive, electrogenic uniport of ions through pores spanning an otherwise poorly permeable lipid bilayer. Among other processes, fluxes through ion channels are responsible for action potentials – large, transient changes in membrane potential which have been known of in plants for over 100 years. Much disparate information on ion channels in plant cells has accumulated over the past few years. In an attempt to synthesize these data, the properties of at least 18 different ion channels are collated in this review. Channels are initially classified according to ion selectivity (Ca2+, Cl−, K+ and H+); then gating characteristics (i.e. control of opening and closing), unitary conductance and pharmacology are used to distinguish further different sub‐types of channels. To provide a background for this overview, the fundamental properties which define ion channels in animal cells, namely conduction, selectivity and gating, are described. Appropriate techniques for the study of ion channels are also assessed. The review concludes with a discussion on the role of ion channels in plant cells, although any comment on functions beyond turgor regulation and general statements about signalling remains largely speculative. The study of ion channels in plant cells is still at an early stage and it is hoped that this review will provide a framework upon which further work in both algae and vascular plants can be based.

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Section: Gating and Kineticsmentioning

confidence: 94%

Tansley Review No. 21 Plant ion channels: whole‐cell and single channel studies

Tester¹

1990

New Phytologist

301

166

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“…The differential equations for this model have been described previously (Bertl et al, 1988;Blatt and Gradmann, 1997), and their solution yields Equations 3 to 8. Steady-state conductances were fitted to Equation 4, and current relaxations were fitted to Equation 6, allowing a minimum of parameter values to vary between data sets representing each of the KAT1 constructs.…”

Section: Reaction-kinetic Modelingmentioning

confidence: 99%

“…The two relaxation constants, l 1 and l 2 , of Equation 4 denote the eigenvalues of the differential rate equations (Bertl et al, 1988;Blatt and Gradmann, 1997), each equivalent to the inverse of the corresponding time constant, and are given by:…”

Section: D105ementioning

confidence: 99%

“…Distances resolved following molecular dynamic equilibration are listed in Table II. exponential terms thus correspond to a series of asymmetric Eyring barriers (d ij Þ d ji ). Now, at any given time t, the macroscopic current I(t) comprises the sum of a steady-state component I s and two exponential components (Bertl et al, 1988;Blatt and Gradmann, 1997):…”

Section: D105ementioning

confidence: 99%

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Voltage-Sensor Transitions of the Inward-Rectifying K+ Channel KAT1 Indicate a Latching Mechanism Biased by Hydration within the Voltage Sensor

et al. 2014

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The Kv-like (potassium voltage-dependent) K + channels at the plasma membrane, including the inward-rectifying KAT1 K + channel of Arabidopsis (Arabidopsis thaliana), are important targets for manipulating K + homeostasis in plants. Gating modification, especially, has been identified as a promising means by which to engineer plants with improved characteristics in mineral and water use. Understanding plant K + channel gating poses several challenges, despite many similarities to that of mammalian Kv and Shaker channel models. We have used site-directed mutagenesis to explore residues that are thought to form two electrostatic countercharge centers on either side of a conserved phenylalanine (Phe) residue within the S2 and S3 a-helices of the voltage sensor domain (VSD) of Kv channels. Consistent with molecular dynamic simulations of KAT1, we show that the voltage dependence of the channel gate is highly sensitive to manipulations affecting these residues. Mutations of the central Phe residue favored the closed KAT1 channel, whereas mutations affecting the countercharge centers favored the open channel. Modeling of the macroscopic current kinetics also highlighted a substantial difference between the two sets of mutations. We interpret these findings in the context of the effects on hydration of amino acid residues within the VSD and with an inherent bias of the VSD, when hydrated around a central Phe residue, to the closed state of the channel.

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“…9A inset; cf. Bertl et al 1988). In addition, two time constants less than 100 ms could be resolved in the frequency distribution of closed durations (Fig.…”

Section: Monovalent-cation Selectivity Of the 49ps K + Channelmentioning

confidence: 93%

Potassium channels from the plasma membrane of rye roots characterized following incorporation into planar lipid bilayers

White

Tester

1992

Planta

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Plasma membrane was purified from roots of rye (Secale cereale L. cv. Rheidol) by aqueous-polymer two-phase partitioning and incorporated into planar bilayers of 1-palmitoyl-2-oleoyl phosphatidylethanolamine by stirring with an osmotic gradient. Since plasmamembrane vesicles were predominantly oriented with their cytoplasmic face internal, when fused to the bilayer the cytoplasmic side of channels faced the trans chamber. In asymmetrical (cis:trans) 280∶100 mM KCl, five distinct K(+)-selective channels were detected with mean chord-conductances (between +30 and -30 mV; volyages cis with respect to trans) of 500 pS, 194 pS, 49 pS, 21 pS and 10 pS. The frequencies of incorporation of these K(+) channels into the bilayer were 48, 21, 50, 10 and 9%, in the order given (data from 159 bilayers). Only the 49 pS channel was characterized further in this paper, but the remarkable diversity of K(+) channels found in this preparation is noteworthy and is the subject of further study. In symmetrical KCl solutions, the 49 pS channel exhibited non-ohmic unitary-current/voltage relationships. The chord-conductance (between +30 and-30 mV) of the channel in symmetrical 100 mM KCl was 39 pS. The unitary current was greater at positive voltages than at corresponding negative voltages and showed considerable rectification with increasing positive and negative voltages. This would represent 'inward rectification' in vivo. Gating of the channel was not voltage-dependent and the channel was open for approx. 80% of the time. Presumably this is not the case in vivo, but we are at present uncertain of the in vivo controls of channel gating. The distribution of channel-open times could be approximated by the sum of two negative exponential functions, yielding two open-state time constants (τo, the apparent mean lifetime of the channel-open state) of 1.0 ms and 5.7 s. The distribution of channel-closed times was best approximated by the sum of three negative exponential functions, yielding time constants (τc, the apparent mean lifetime of the channel-closed state) of 1.1 ms, 51 ms and 11 s. This indicates at least a five-state kinetic model for the activity of the channel. The selectivity of the 49 pS channel, determined from both reversal potentials under biionic conditions (100 mM KCl∶100 mM cation chloride) and from conductance measurements in symmetrical 100 mM cation chloride, was Rb(+)≥ K(+)> Cs(+) > Na(+) > Li(+) > tetraethylammonium (TEA(+)). The 49 pS channel was reversibly inhibited by quinine (1 mM) but TEA(+) (10 mM), Ba(2+) (3 mM), Ca(2+) (1 mM), 4-aminopyridine (1 mM) and charybdotoxin (3 μM) were without effect when applied to the extracellular (cis) surface.

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Slow kinetics of a potassium channel inAcetabularia

Cited by 31 publications

References 10 publications

Tansley Review No. 21 Plant ion channels: whole‐cell and single channel studies

Tansley Review No. 21 Plant ion channels: whole‐cell and single channel studies

Voltage-Sensor Transitions of the Inward-Rectifying K+ Channel KAT1 Indicate a Latching Mechanism Biased by Hydration within the Voltage Sensor

Potassium channels from the plasma membrane of rye roots characterized following incorporation into planar lipid bilayers

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