scholarly journals External barium influences the gating charge movement of Shaker potassium channels

1997 ◽  
Vol 72 (1) ◽  
pp. 77-84 ◽  
Author(s):  
R.S. Hurst ◽  
M.J. Roux ◽  
L. Toro ◽  
E. Stefani
Keyword(s):  
Potassium Channels ◽  
Charge Movement ◽  
Gating Charge ◽  
Shaker Potassium Channels

scholarly journals Activation of Shaker Potassium Channels

1998 ◽  
Vol 111 (2) ◽  
pp. 271-294 ◽  
Author(s):  
N.E. Schoppa ◽  
F.J. Sigworth
Keyword(s):  
Potassium Channels ◽  
Conformational Changes ◽  
Average Charge ◽  
Xenopus Laevis Oocytes ◽  
Activation Process ◽  
Subsequent Paper ◽  
Charge Movement ◽  
Partial Charges ◽  
Activation Gating ◽  
Shaker Potassium Channels

The conformational changes associated with activation gating in Shaker potassium channels are functionally characterized in patch-clamp recordings made from Xenopus laevis oocytes expressing Shaker channels with fast inactivation removed. Estimates of the forward and backward rates for transitions are obtained by fitting exponentials to macroscopic ionic and gating current relaxations at voltage extremes, where we assume that transitions are unidirectional. The assignment of different rates is facilitated by using voltage protocols that incorporate prepulses to preload channels into different distributions of states, yielding test currents that reflect different subsets of transitions. These data yield direct estimates of the rate constants and partial charges associated with three forward and three backward transitions, as well as estimates of the partial charges associated with other transitions. The partial charges correspond to an average charge movement of 0.5 e0 during each transition in the activation process. This value implies that activation gating involves a large number of transitions to account for the total gating charge displacement of 13 e0. The characterization of the gating transitions here forms the basis for constraining a detailed gating model to be described in a subsequent paper of this series.

scholarly journals Specificity of Charge-carrying Residues in the Voltage Sensor of Potassium Channels

2004 ◽  
Vol 123 (3) ◽  
pp. 205-216 ◽  
Author(s):  
Christopher A. Ahern ◽  
Richard Horn
Keyword(s):  
Potassium Channels ◽  
Electric Field ◽  
Protein A ◽  
Membrane Lipid ◽  
Voltage Sensor ◽  
Charge Movement ◽  
Gating Currents ◽  
Gating Charge ◽  
Channel Opening ◽  
Positively Charged

Positively charged voltage sensors of sodium and potassium channels are driven outward through the membrane's electric field upon depolarization. This movement is coupled to channel opening. A recent model based on studies of the KvAP channel proposes that the positively charged voltage sensor, christened the “voltage-sensor paddle”, is a peripheral domain that shuttles its charged cargo through membrane lipid like a hydrophobic cation. We tested this idea by attaching charged adducts to cysteines introduced into the putative voltage-sensor paddle of Shaker potassium channels and measuring fractional changes in the total gating charge from gating currents. The only residues capable of translocating attached charges through the membrane-electric field are those that serve this function in the native channel. This remarkable specificity indicates that charge movement involves highly specialized interactions between the voltage sensor and other regions of the protein, a mechanism inconsistent with the paddle model.

Molecular basis of gating charge immobilization in Shaker potassium channels

Science ◽  
1991 ◽  
Vol 254 (5032) ◽  
pp. 679-683 ◽  
Author(s):  
F Bezanilla ◽  
E Perozo ◽  
D. Papazian ◽  
E Stefani
Keyword(s):  
Potassium Channels ◽  
Molecular Basis ◽  
Gating Charge ◽  
Shaker Potassium Channels

scholarly journals Electrostatics and the Gating Pore of Shaker Potassium Channels

2001 ◽  
Vol 117 (1) ◽  
pp. 69-90 ◽  
Author(s):  
Leon D. Islas ◽  
Fred J. Sigworth
Keyword(s):  
Charge Movement ◽  
Transmembrane Helices ◽  
Gating Currents ◽  
Conical Cavity ◽  
K Channels ◽  
Gating Charge ◽  
Voltage Dependent ◽  
Shaker Potassium Channels ◽  
Electrostatic Calculations ◽  
S4 Segment

Various experiments have suggested that the S4 segment in voltage-dependent Na+ and K+ channels is in contact with a solvent-accessible cavity. We explore the consequences of the existence of such a cavity through the electrostatic effects on the gating currents of Shaker K+ channels under conditions of reduced ionic strength S. We observe that ∼10-fold reductions of intracellular S produce reductions of the measured gating charge of ∼10%. These effects continue at even lower values of S. The reduction of gating charge when S is reduced by 10-fold at the extracellular surface is much smaller (∼2%). Shifts of the Q(V) curve because of a reduced S are small (<10 mV in size), which is consistent with very little fixed surface charge. Continuum electrostatic calculations show that the S effects on gating charge can be explained by the alteration of the local potential in an intracellular conical cavity of 20–24-Å depth and 12-Å aperture, and a smaller extracellular cavity of 3-Å depth and the same aperture. In this case, the attenuation of the membrane potential at low S leads to reduction of the apparent gating charge. We suggest that this cavity is made by a bundle of transmembrane helices, and that the gating charge movement occurs by translocation of charged residues across a thin septum of ∼3–7 Å thickness.

The size of gating charge in wild-type and mutant Shaker potassium channels

Science ◽  
1992 ◽  
Vol 255 (5052) ◽  
pp. 1712-1715 ◽  
Author(s):  
N. Schoppa ◽  
K McCormack ◽  
M. Tanouye ◽  
F. Sigworth
Keyword(s):  
Potassium Channels ◽  
Wild Type ◽  
Gating Charge ◽  
Shaker Potassium Channels

scholarly journals A Dipeptidyl Aminopeptidase–like Protein Remodels Gating Charge Dynamics in Kv4.2 Channels

2006 ◽  
Vol 128 (6) ◽  
pp. 745-753 ◽  
Author(s):  
Kevin Dougherty ◽  
Manuel Covarrubias
Keyword(s):  
Membrane Potentials ◽  
Charge Movement ◽  
Transmembrane Segment ◽  
Gating Currents ◽  
Voltage Sensing ◽  
Charge Voltage ◽  
Charge Dynamics ◽  
Gating Charge ◽  
Kv4 Channels ◽  
Dipeptidyl Aminopeptidase

Dipeptidyl aminopeptidase–like proteins (DPLPs) interact with Kv4 channels and thereby induce a profound remodeling of activation and inactivation gating. DPLPs are constitutive components of the neuronal Kv4 channel complex, and recent observations have suggested the critical functional role of the single transmembrane segment of these proteins (Zagha, E., A. Ozaita, S.Y. Chang, M.S. Nadal, U. Lin, M.J. Saganich, T. McCormack, K.O. Akinsanya, S.Y. Qi, and B. Rudy. 2005. J. Biol. Chem. 280:18853–18861). However, the underlying mechanism of action is unknown. We hypothesized that a unique interaction between the Kv4.2 channel and a DPLP found in brain (DPPX-S) may remodel the channel's voltage-sensing domain. To test this hypothesis, we implemented a robust experimental system to measure Kv4.2 gating currents and study gating charge dynamics in the absence and presence of DPPX-S. The results demonstrated that coexpression of Kv4.2 and DPPX-S causes a −26 mV parallel shift in the gating charge-voltage (Q-V) relationship. This shift is associated with faster outward movements of the gating charge over a broad range of relevant membrane potentials and accelerated gating charge return upon repolarization. In sharp contrast, DPPX-S had no effect on gating charge movements of the Shaker B Kv channel. We propose that DPPX-S destabilizes resting and intermediate states in the voltage-dependent activation pathway, which promotes the outward gating charge movement. The remodeling of gating charge dynamics may involve specific protein–protein interactions of the DPPX-S's transmembrane segment with the voltage-sensing and pore domains of the Kv4.2 channel. This mechanism may determine the characteristic fast operation of neuronal Kv4 channels in the subthreshold range of membrane potentials.

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