|
|
|
|
|
|
|
||
Article |
Dual Roles of Surface Charge Screening and Pore Block
Address correspondence to James N. Weiss, Division of Cardiology, Rm. 3645, MRL Building, UCLA School of Medicine, Los Angeles, CA 90095. Fax: (310) 206-5777; E-mail: jweiss{at}mednet.ucla.edu
Inward rectification in strong inward rectifiers such as Kir2.1 is attributed to voltage-dependent block by intracellular polyamines and Mg2+. Block by the polyamine spermine has a complex voltage dependence with shallow and steep components and complex concentration dependence. To understand the mechanism, we measured macroscopic Kir2.1 currents in excised inside-out giant patches from Xenopus oocytes expressing Kir2.1, and single channel currents in the inside-out patches from COS7 cells transfected with Kir2.1. We found that as spermine concentration or voltage increased, the shallow voltage-dependent component of spermine block at more negative voltages was caused by progressive reduction in the single channel current amplitude, without a decrease in open probability. We attributed this effect to spermine screening negative surface charges involving E224 and E299 near the inner vestibule of the channel, thereby reducing K ion permeation rate. This idea was further supported by experiments in which increasing ionic strength also decreased Kir2.1 single channel amplitude, and by mutagenesis experiments showing that this component of spermine block decreased when E224 and E299, but not D172, were neutralized. The steep voltage-dependent component of block at more depolarized voltages was attributed to spermine migrating deeper into the pore and causing fast open channel block. A quantitative model incorporating both features showed excellent agreement with the steady-state and kinetic data. In addition, this model accounts for previously described substate behavior induced by a variety of Kir2.1 channel blockers.
Key Words: K+ channels • inward rectification • polyamine • spermine • modeling
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
 |
|
  L.-H. Xie, S. A. John, B. Ribalet, and J. N. Weiss Phosphatidylinositol-4,5-bisphosphate (PIP2) regulation of strong inward rectifier Kir2.1 channels: multilevel positive cooperativity J. Physiol., April 1, 2008; 586(7): 1833 - 1848. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
K. Ishihara and D.-H. Yan Low-affinity spermine block mediating outward currents through Kir2.1 and Kir2.2 inward rectifier potassium channels J. Physiol., September 15, 2007; 583(3): 891 - 908. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H. T. Kurata, W. W. Cheng, C. Arrabit, P. A. Slesinger, and C. G. Nichols The Role of the Cytoplasmic Pore in Inward Rectification of Kir2.1 Channels J. Gen. Physiol., July 30, 2007; 130(2): 145 - 155. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. Zhang, X. Niu, T. I. Brelidze, and K. L. Magleby Ring of Negative Charge in BK Channels Facilitates Block by Intracellular Mg2+ and Polyamines through Electrostatics J. Gen. Physiol., July 31, 2006; 128(2): 185 - 202. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. Fujiwara and Y. Kubo Functional Roles of Charged Amino Acid Residues on the Wall of the Cytoplasmic Pore of Kir2.1 J. Gen. Physiol., March 27, 2006; 127(4): 401 - 419. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
B. K. Panama and A. N. Lopatin Differential polyamine sensitivity in inwardly rectifying Kir2 potassium channels J. Physiol., March 1, 2006; 571(2): 287 - 302. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
L.-H. Xie, S. A. John, B. Ribalet, and J. N. Weiss Long Polyamines Act as Cofactors in PIP2 Activation of Inward Rectifier Potassium (Kir2.1) Channels J. Gen. Physiol., November 28, 2005; 126(6): 541 - 549. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S.-H. Yeh, H.-K. Chang, and R.-C. Shieh Electrostatics in the Cytoplasmic Pore Produce Intrinsic Inward Rectification in Kir2.1 Channels J. Gen. Physiol., November 28, 2005; 126(6): 551 - 562. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
E. W Newell and L. C Schlichter Integration of K+ and Cl- currents regulate steady-state and dynamic membrane potentials in cultured rat microglia J. Physiol., September 15, 2005; 567(3): 869 - 890. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. Loussouarn, L. J. Marton, and C. G. Nichols Molecular Basis of Inward Rectification: Structural Features of the Blocker Defined by Extended Polyamine Analogs Mol. Pharmacol., August 1, 2005; 68(2): 298 - 304. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H.-G. Shin, Y. Xu, and Z. Lu Evidence for Sequential Ion-binding Loci along the Inner Pore of the IRK1 Inward-rectifier K+ Channel J. Gen. Physiol., July 25, 2005; 126(2): 123 - 135. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H.-G. Shin and Z. Lu Mechanism of the Voltage Sensitivity of IRK1 Inward-rectifier K+ Channel Block by the Polyamine Spermine J. Gen. Physiol., March 28, 2005; 125(4): 413 - 426. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D.-H. Yan and K. Ishihara Two Kir2.1 channel populations with different sensitivities to Mg2+ and polyamine block: a model for the cardiac strong inward rectifier K+ channel J. Physiol., March 15, 2005; 563(3): 725 - 744. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H.-K. Chang, S.-H. Yeh, and R.-C. Shieh A Ring of Negative Charges in the Intracellular Vestibule of Kir2.1 Channel Modulates K+ Permeation Biophys. J., January 1, 2005; 88(1): 243 - 254. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
L.-H. Xie, S. A John, B. Ribalet, and J. N Weiss Regulation of gating by negative charges in the cytoplasmic pore in the Kir2.1 channel J. Physiol., November 15, 2004; 561(1): 159 - 168. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. T. Kurata, L. R. Phillips, T. Rose, G. Loussouarn, S. Herlitze, H. Fritzenschaft, D. Enkvetchakul, C. G. Nichols, and T. Baukrowitz Molecular Basis of Inward Rectification: Polyamine Interaction Sites Located by Combined Channel and Ligand Mutagenesis J. Gen. Physiol., October 25, 2004; 124(5): 541 - 554. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. A. John, L.-H. Xie, and J. N. Weiss Mechanism of Inward Rectification in Kir Channels J. Gen. Physiol., April 26, 2004; 123(5): 623 - 625. [Full Text] [PDF]
|
|
|
|
|
|
K. Ishihara and T. Ehara Two modes of polyamine block regulating the cardiac inward rectifier K+ current IK1 as revealed by a study of the Kir2.1 channel expressed in a human cell line J. Physiol., April 1, 2004; 556(1): 61 - 78. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
L. R. Phillips and C. G. Nichols Ligand-induced Closure of Inward Rectifier Kir6.2 Channels Traps Spermine in the Pore J. Gen. Physiol., November 24, 2003; 122(6): 795 - 805. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H.-K. Chang and R.-C. Shieh Conformational Changes in Kir2.1 Channels during NH4+-induced Inactivation J. Biol. Chem., January 3, 2003; 278(2): 908 - 918. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. Fujiwara and Y. Kubo Ser165 in the Second Transmembrane Region of the Kir2.1 Channel Determines its Susceptibility to Blockade by Intracellular Mg2+ J. Gen. Physiol., October 29, 2002; 120(5): 677 - 693. [Abstract] [Full Text] [PDF]
|
|
|
|
