scholarly journals Block of inward rectification by intracellular H+ in immature oocytes of the starfish Mediaster aequalis.

1982 ◽  
Vol 79 (1) ◽  
pp. 115-130 ◽  
Author(s):  
W J Moody ◽  
S Hagiwara
Keyword(s):  
Intracellular Ph ◽  
Voltage Dependence ◽  
Sea Water ◽  
Inward Rectification ◽  
Activation Kinetics ◽  
Internal Ph ◽  
A Site ◽  
The Relationship ◽  
Inwardly Rectifying ◽  
Kinetics Of

Intracellular pH was recorded in immature starfish oocytes using pH-sensitive microelectrodes, and inwardly rectifying potassium currents were measured under voltage clamp. When the intracellular pH was lowered using acetate-buffered artificial sea water from the normal value of 7.09 to 5.9, inward rectification was completely blocked. The relationship between inward rectification and internal pH between 7.09 and 5.9 could be fit by a titration curve for the binding of three H ions to a site with a pK of 6.26 to block the channel. The H+ block showed no voltage dependence, and the activation kinetics of the inwardly rectifying currents were not affected by the changes in internal pH.

scholarly journals Locale and chemistry of spermine binding in the archetypal inward rectifier Kir2.1

2010 ◽  
Vol 135 (5) ◽  
pp. 495-508 ◽  
Author(s):  
Harley T. Kurata ◽  
Emily A. Zhu ◽  
Colin G. Nichols
Keyword(s):  
Binding Site ◽  
Voltage Dependence ◽  
Inward Rectifier ◽  
Selectivity Filter ◽  
Inward Rectification ◽  
Before And After ◽  
Voltage Dependent ◽  
Inwardly Rectifying ◽  
Kinetics Of

Polyamine block of inwardly rectifying potassium (Kir) channels underlies their steep voltage dependence observed in vivo. We have examined the potency, voltage dependence, and kinetics of spermine block in dimeric Kir2.1 constructs containing one nonreactive subunit and one cysteine-substituted subunit before and after modification by methanethiosulfonate (MTS) reagents. At position 169C (between the D172 “rectification controller” and the selectivity filter), modification by either 2-aminoethyl MTS (MTSEA) or 2-(trimethylammonium)ethyl MTS (MTSET) reduced the potency and voltage dependence of spermine block, consistent with this position overlapping the spermine binding site. At position 176C (between D172 and the M2 helix bundle crossing), modification by MTSEA also weakened spermine block. In contrast, MTSET modification of 176C dramatically slowed the kinetics of spermine unblock, with almost no effect on potency or voltage dependence. The data are consistent with MTSET modification of 176C introducing a localized barrier in the inner cavity, resulting in slower spermine entry into and exit from a “deep” binding site (likely between the D172 rectification controller and the selectivity filter), but leaving the spermine binding site mostly unaffected. These findings constrain the location of deep spermine binding that underlies steeply voltage-dependent block, and further suggest important chemical details of high affinity binding of spermine in Kir2.1 channels—the archetypal model of strong inward rectification.

Intracellular H+ inhibits a cloned rat kidney outer medulla K+ channel expressed in Xenopus oocytes

1995 ◽  
Vol 268 (5) ◽  
pp. C1173-C1178 ◽  
Author(s):  
T. D. Tsai ◽  
M. E. Shuck ◽  
D. P. Thompson ◽  
M. J. Bienkowski ◽  
K. S. Lee
Keyword(s):  
Xenopus Oocytes ◽  
Rat Kidney ◽  
Ph Sensitivity ◽  
Resting Potential ◽  
K Channel ◽  
K Current ◽  
A Site ◽  
The Relationship ◽  
Inwardly Rectifying ◽  
External Ph

The pH sensitivity of a cloned rat kidney K+ channel, ROMK1, was examined after expression in Xenopus oocytes. Membrane currents and intracellular pH (pHi) were concomitantly monitored by the two-microelectrode voltage-clamp technique and a pH-sensitive microelectrode. Oocytes injected with ROMK1 cRNA developed a hyperpolarized resting potential of -98.7 +/- 0.98 mV and a slightly inwardly rectifying Ba(2+)-sensitive K+ current. Lowering external pH from 7.4 to 6.7 using membrane-permeable acetate buffer reduced measured pHi from 7.2 to 6.6 and reduced the ROMK1 current by 80%. The H+ blockade of ROMK1 currents was voltage independent. The relationship between ROMK1 slope conductance and pHi fitted to a titration curve suggested binding of four H+ to a site with a pK of 6.79. Extracellular acidification from pH 7.4 to 6.0 using membrane-impermeable biphthalate buffer had no effect on the ROMK1 current. The pH sensitivity of the ROMK1 channel is similar to that reported for a small-conductance native kidney K+ channel.

scholarly journals Permeation and Gating of an Inwardly Rectifying Potassium Channel

1998 ◽  
Vol 112 (4) ◽  
pp. 433-446 ◽  
Author(s):  
Han Choe ◽  
Henry Sackin ◽  
Lawrence G. Palmer
Keyword(s):  
Voltage Dependence ◽  
Divalent Cations ◽  
K Channel ◽  
Single Channels ◽  
Closed State ◽  
Inwardly Rectifying Potassium Channel ◽  
Well Model ◽  
K Concentration ◽  
Inwardly Rectifying ◽  
Kinetics Of

Permeation, gating, and their interrelationship in an inwardly rectifying potassium (K+) channel, ROMK2, were studied using heterologous expression in Xenopus oocytes. Patch-clamp recordings of single channels were obtained in the cell-attached mode. The gating kinetics of ROMK2 were well described by a model having one open and two closed states. One closed state was short lived (∼1 ms) and the other was longer lived (∼40 ms) and less frequent (∼1%). The long closed state was abolished by EDTA, suggesting that it was due to block by divalent cations. These closures exhibit a biphasic voltage dependence, implying that the divalent blockers can permeate the channel. The short closures had a similar biphasic voltage dependence, suggesting that they could be due to block by monovalent, permeating cations. The rate of entering the short closed state varied with the K+ concentration and was proportional to current amplitude, suggesting that permeating K+ ions may be related to the short closures. To explain the results, we propose a variable intrapore energy well model in which a shallow well may change into a deep one, resulting in a normally permeant K+ ion becoming a blocker of its own channel.

scholarly journals Mg2+-dependent Gating and Strong Inward Rectification of the Cation Channel TRPV6

2003 ◽  
Vol 121 (3) ◽  
pp. 245-260 ◽  
Author(s):  
Thomas Voets ◽  
Annelies Janssens ◽  
Jean Prenen ◽  
Guy Droogmans ◽  
Bernd Nilius
Keyword(s):  
Divalent Cations ◽  
Inward Rectification ◽  
Electrical Field ◽  
Gating Mechanism ◽  
Voltage Dependent ◽  
A Site ◽  
Inwardly Rectifying ◽  
Inside Out ◽  
Aspartate Residue

TRPV6 (CaT1/ECaC2), a highly Ca2+-selective member of the TRP superfamily of cation channels, becomes permeable to monovalent cations in the absence of extracellular divalent cations. The monovalent currents display characteristic voltage-dependent gating and almost absolute inward rectification. Here, we show that these two features are dependent on the voltage-dependent block/unblock of the channel by intracellular Mg2+. Mg2+ blocks the channel by binding to a site within the transmembrane electrical field where it interacts with permeant cations. The block is relieved at positive potentials, indicating that under these conditions Mg2+ is able to permeate the selectivity filter of the channel. Although sizeable outward monovalent currents were recorded in the absence of intracellular Mg2+, outward conductance is still ∼10 times lower than inward conductance under symmetric, divalent-free ionic conditions. This Mg2+-independent rectification was preserved in inside-out patches and not altered by high intracellular concentrations of spermine, indicating that TRPV6 displays intrinsic rectification. Neutralization of a single aspartate residue within the putative pore loop abolished the Mg2+ sensitivity of the channel, yielding voltage-independent, moderately inwardly rectifying monovalent currents in the presence of intracellular Mg2+. The effects of intracellular Mg2+ on TRPV6 are partially reminiscent of the gating mechanism of inwardly rectifying K+ channels and may represent a novel regulatory mechanism for TRPV6 function in vivo.

Mutations throughout the S6 region of the hKv1.5 channel alter the stability of the activation gate

2002 ◽  
Vol 282 (1) ◽  
pp. C161-C171 ◽  
Author(s):  
Thomas C. Rich ◽  
Sarita W. Yeola ◽  
Michael M. Tamkun ◽  
Dirk J. Snyders
Keyword(s):  
Voltage Dependence ◽  
Channel Gating ◽  
Temperature Sensitive ◽  
Voltage Sensitivity ◽  
Wild Type ◽  
Activation Kinetics ◽  
Deactivation Kinetics ◽  
Activation Gate ◽  
The Stability ◽  
Kinetics Of

First published September 21, 2001; 10.1152/ ajpcell.00232.2001.—The S6 segment of voltage-gated K+ channels is thought to contribute to the gate that opens the central permeation pathway. Here we present evidence that mutations throughout the cytoplasmic end of S6 strongly influence hKv1.5 channel gating characteristics. Modification of hKv1.5 at positions T505, V512, and S515 resulted in large negative shifts in the voltage dependence of activation, whereas modifications at position Y519 resulted in negative (Y519N) and positive (Y519F) shifts. When adjusted for the altered voltage sensitivity, activation kinetics of mutated channels were similar to those of the wild-type (WT) channel; however, deactivation kinetics of mutations T505I, T505V, V512A, and V512M [time constant (τ) = 35, 250, 170, and 420 ms, respectively] were still slower than WT (τ = 8.3 ms). In addition, deactivation of WT channels was highly temperature sensitive. However, deactivation of T505I and V512A channels was largely temperature insensitive. Together, these data suggest that mutations in S6 decouple activation from deactivation by altering the open-state stability and that residues on both sides of the highly conserved Pro-X-Pro sequence influence the movement of S6 during channel gating.

scholarly journals Kir4.1/Kir5.1 channels possess strong intrinsic inward rectification determined by a voltage-dependent K+-flux gating mechanism

2021 ◽  
Vol 153 (5) ◽  
Author(s):  
Leticia G. Marmolejo-Murillo ◽  
Iván A. Aréchiga-Figueroa ◽  
Eloy G. Moreno-Galindo ◽  
Tania Ferrer ◽  
Rodrigo Zamora-Cárdenas ◽  
...  
Keyword(s):  
Voltage Dependence ◽  
Inward Rectification ◽  
Potassium Ions ◽  
Cellular Functions ◽  
Kir Channels ◽  
Gating Mechanism ◽  
Dependent Behavior ◽  
Voltage Dependent ◽  
Inwardly Rectifying ◽  
Dependent Mechanism

Inwardly rectifying potassium (Kir) channels are broadly expressed in both excitable and nonexcitable tissues, where they contribute to a wide variety of cellular functions. Numerous studies have established that rectification of Kir channels is not an inherent property of the channel protein itself, but rather reflects strong voltage dependence of channel block by intracellular cations, such as polyamines and Mg2+. Here, we identify a previously unknown mechanism of inward rectification in Kir4.1/Kir5.1 channels in the absence of these endogenous blockers. This novel intrinsic rectification originates from the voltage-dependent behavior of Kir4.1/Kir5.1, which is generated by the flux of potassium ions through the channel pore; the inward K+-flux induces the opening of the gate, whereas the outward flux is unable to maintain the gate open. This gating mechanism powered by the K+-flux is convergent with the gating of PIP2 because, at a saturating concentration, PIP2 greatly reduces the inward rectification. Our findings provide evidence of the coexistence of two rectification mechanisms in Kir4.1/Kir5.1 channels: the classical inward rectification induced by blocking cations and an intrinsic voltage-dependent mechanism generated by the K+-flux gating.

Inward rectification in the inner segment of single retinal cone photoreceptors

1990 ◽  
Vol 64 (6) ◽  
pp. 1917-1928 ◽  
Author(s):  
A. V. Maricq ◽  
J. I. Korenbrot
Keyword(s):  
Voltage Dependence ◽  
Reversal Potential ◽  
Input Resistance ◽  
Resting Potential ◽  
Inward Rectification ◽  
Delayed Rectifier ◽  
Light Illumination ◽  
Cone Photoreceptors ◽  
Voltage Dependent ◽  
Kinetics Of

1. Single cone photoreceptors were dissociated from the retina of a lizard with the aid of papain. The majority of the cells lost their outer segments but had well-preserved, large synaptic pedicles. Electrical properties of the cells were studied with tight-seal electrodes in the whole cell configuration. On the average, cone inner segments had a resting potential of -55 mV, and at this potential their input resistance was 2.6 G omega and their capacitance was 8 pF. 2. Under current clamp the cones exhibited a pronounced anomalous voltage rectification in response to hyperpolarizing currents. The voltage rectification was eliminated by external Cs+. 3. The Cs(+)-sensitive current underlying voltage rectification was isolated by blocking other currents present in the cone. Co2+ blocked a voltage-dependent Ca2+ current and a Ca2(+)-dependent Cl- current, and tetraethylammonium (TEA)+ blocked a delayed-rectifier K+ current. 4. The Cs(+)-sensitive current was activated by hyperpolarization to potentials more negative than -50 mV, and its current-voltage (I-V) relationship exhibited inward rectification. 5. The inward-rectifying current was selective for K+, but not exclusively. Increasing external K+ concentration 10-fold shifted the reversal potential by 13 mV. If Na ions also permeate through the inward-rectifying channels, the ratio of permeabilities (PK+/PNa+) in normal solution is approximately 3.9. 6. The kinetics of the inward-rectifying current were described by the sum of two exponentials, the amplitudes and time constants of which were voltage dependent. 7. The voltage dependence of the inward-rectifying current was described by Boltzmann's function, with half-maximum activation at -79 mV and a steepness parameter of 7.5 mV. 8. The voltage dependence and kinetics of the inward-rectifying current suggest that it is inactive in a cone photoreceptor in the dark. However, it becomes activated in the course of large hyperpolarizations generated by bright-light illumination. This activity will modify the waveform of the photovoltage--the current will generate a depolarizing component that opposes the light-generated hyperpolarization.

Fast and Slow Activation Kinetics of Voltage-Gated Sodium Channels in Molluscan Neurons

1997 ◽  
Vol 77 (5) ◽  
pp. 2373-2384 ◽  
Author(s):  
William F. Gilly ◽  
Rhanor Gillette ◽  
Matthew McFarlane
Keyword(s):  
Sodium Channels ◽  
Voltage Dependence ◽  
Na Channel ◽  
Molluscan Neurons ◽  
Na Channels ◽  
Activation Kinetics ◽  
Voltage Gated ◽  
Voltage Gated Sodium Channels ◽  
Voltage Dependent ◽  
Kinetics Of

Gilly, William F., Rhanor Gillette, and Matthew McFarlane. Fast and slow activation kinetics of voltage-gated sodium channels in molluscan neurons. J. Neurophysiol. 77: 2373–2384, 1997. Whole cell patch-clamp recordings of Na current ( I Na) were made under identical experimental conditions from isolated neurons from cephalopod ( Loligo, Octopus) and gastropod ( Aplysia, Pleurobranchaea, Doriopsilla) species to compare properties of activation gating. Voltage dependence of peak Na conductance ( g Na) is very similar in all cases, but activation kinetics in the gastropod neurons studied are markedly slower. Kinetic differences are very pronounced only over the voltage range spanned by the g Na-voltage relation. At positive and negative extremes of voltage, activation and deactivation kinetics of I Na are practically indistinguishable in all species studied. Voltage-dependent rate constants underlying activation of the slow type of Na channel found in gastropods thus appear to be much more voltage dependent than are the equivalent rates in the universally fast type of channel that predominates in cephalopods. Voltage dependence of inactivation kinetics shows a similar pattern and is representative of activation kinetics for the two types of Na channels. Neurons with fast Na channels can thus make much more rapid adjustments in the number of open Na channels at physiologically relevant voltages than would be possible with only slow Na channels. This capability appears to be an adaptation that is highly evolved in cephalopods, which are well known for their high-speed swimming behaviors. Similarities in slow and fast Na channel subtypes in molluscan and mammalian neurons are discussed.

Heterogeneity of IK1 in the mouse heart

2007 ◽  
Vol 293 (6) ◽  
pp. H3558-H3567 ◽  
Author(s):  
Brian K. Panama ◽  
Meredith McLerie ◽  
Anatoli N. Lopatin
Keyword(s):  
Potassium Current ◽  
Inward Rectification ◽  
Mouse Heart ◽  
Regional Heterogeneity ◽  
Activation Kinetics ◽  
Ventricular Cells ◽  
Subunit Stoichiometry ◽  
Quantitative Explanation ◽  
Kinetics Of ◽  
Kir2.1 Channel

Previous studies have shown that cardiac inward rectifier potassium current ( IK1) channels are heteromers of distinct Kir2 subunits and suggested that species- and tissue-dependent expression of these subunits may underlie variability of IK1. In this study, we investigated the contribution of the slowly activating Kir2.3 subunit and free intracellular polyamines (PAs) to variability of IK1 in the mouse heart. The kinetics of activation was measured in Kir2 concatemeric tetramers with known subunit stoichiometry. Inclusion of only one Kir2.3 subunit to a Kir2.1 channel led to an approximate threefold slowing of activation kinetics, with greater slowing on subsequent additions of Kir2.3 subunits. Activation kinetics of IK1 in both ventricles and both atria was found to correspond to fast-activating Kir2.1/Kir2.2 channels, suggesting no major contribution of Kir2.3 subunits. In contrast, IK1 displayed significant variation in both the current density and inward rectification, suggesting involvement of intracellular PAs. The total levels of PAs were similar across the mouse heart. Measurements of the free intracellular PAs in isolated myocytes, using transgenically expressed Kir2.1 channels as PA sensors, revealed “microheterogeneity” of IK1 rectification as well as lower levels of free PAs in atrial myocytes compared with ventricular cells. These findings provide a quantitative explanation for the regional heterogeneity of IK1.

Colonialism and the Highland Clearances

2017 ◽  
Vol 8 (1) ◽  
pp. 22-48 ◽  
Author(s):  
Iain Mackinnon
Keyword(s):  
Industrial Development ◽  
Comparative Approach ◽  
Indigenous Research ◽  
Internal Colonialism ◽  
New Approach ◽  
A Site ◽  
Relationship Of ◽  
The Relationship ◽  
Imperial State ◽  
Late Modern

This article employs a new approach to studying internal colonialism in northern Scotland during the 18th and 19th centuries. A common approach to examining internal colonial situations within modern state territories is to compare characteristics of the internal colonial situation with attested attributes of external colonial relations. Although this article does not reject the comparative approach, it seeks to avoid criticisms that this approach can be misleading by demonstrating that promoters and managers of projects involving land use change, territorial dispossession and industrial development in the late modern Gàidhealtachd consistently conceived of their work as projects of colonization. It further argues that the new social, cultural and political structures these projects imposed on the area's indigenous population correspond to those found in other colonial situations, and that racist and racialist attitudes towards Gaels of the time are typical of those in colonial situations during the period. The article concludes that the late modern Gàidhealtachd has been a site of internal colonization where the relationship of domination between colonizer and colonized is complex, longstanding and occurring within the imperial state. In doing so it demonstrates that the history and present of the Gaels of Scotland belongs within the ambit of an emerging indigenous research paradigm.

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