| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
We recently characterized two distinct mechanisms by which the polyamine spermine blocks Kir2.1 channels: (1) by reduction of negative surface charges in the cytoplasmic pore, thereby reducing single-channel conductance, and (2) by direct open channel transmembrane pore block. The extent to which the surface charge reduction component is mediated by passive surface charge screening versus binding of polyamines to these charges, as well as the extent to which the surface charge reduction and pore block mechanisms are synergistic, versus simply additive, was not established. To address these issues, macroscopic currents were recorded from inside-out giant patches from Xenopus oocytes and from single-channel currents from COS7 cells expressing wild-type and mutant Kir2.1 channels, during exposure to polyamines of varying length and charge. The surface charge reduction component was decreased when polyamine charge (at constant length) was decreased from 4 (spermine) to 2 (diamine 10, DA10). Moreover, the surface charge reduction component of block involved more than passive surface charge screening and required binding of polyamines to the cytoplasmic pore, since it was eliminated when polyamine length was shortened below six alkyl groups. Loss of surface charge reduction also dramatically affected open channel pore block. The latter consisted of two subcomponents with fast and slow kinetics, respectively. The slow subcomponent decreased as blocker length decreased (DA10, DA8 and DA6), whereas the fast subcomponent was sensitive to blocker charge (spermine vs. DA10). Neutralization of E224 and E299, which eliminated the surface charge reduction component of block, also eliminated the fast subcomponent of pore block. Neutralization of D172 had no effect on the surface charge reduction component, but weakened both of the subcomponents of pore block. These findings can be accounted for by a model in which the negative charges at E224, E299 and D172 act in a concerted manner to coordinate the surface charge reduction and open channel components of polyamine block. In this model, the binding of polyamines to surface charges E224 and E299 pre-positions them in the cytoplasmic pore in a manner that directly facilitates their entry and exit from a transmembrane pore-occluding site involving D172. A molecular model using the recently reported 1.8 Å resolution structure of the inward-rectifier cytoplasmic pore, adapted to Kir2.1, is consistent with longer polyamines binding at their positively charged ends to the E224 and E299 positions in the same subunit, potentially accommodating four polyamine molecules per channel.
This article has been cited by other articles:
|
|
 |
|
  H. T. Kurata, K. Diraviyam, L. J. Marton, and C. G. Nichols Blocker Protection by Short Spermine Analogs: Refined Mapping of the Spermine Binding Site in a Kir Channel Biophys. J., October 15, 2008; 95(8): 3827 - 3839. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Hassinen, V. Paajanen, and M. Vornanen A novel inwardly rectifying K+ channel, Kir2.5, is upregulated under chronic cold stress in fish cardiac myocytes J. Exp. Biol., July 1, 2008; 211(13): 2162 - 2171. [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]
|
|
|
|
 |
|
 M. Hassinen, V. Paajanen, J. Haverinen, H. Eronen, and M. Vornanen Cloning and expression of cardiac Kir2.1 and Kir2.2 channels in thermally acclimated rainbow trout Am J Physiol Regulatory Integrative Comp Physiol, June 1, 2007; 292(6): R2328 - R2339. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. Bichet, M. Grabe, Y. N. Jan, and L. Y. Jan Electrostatic interactions in the channel cavity as an important determinant of potassium channel selectivity PNAS, September 26, 2006; 103(39): 14355 - 14360. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Grabe, D. Bichet, X. Qian, Y. N. Jan, and L. Y. Jan K+ channel selectivity depends on kinetic as well as thermodynamic factors PNAS, September 26, 2006; 103(39): 14361 - 14366. [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]
|
|
|
|
|
|
S. M. Y. Makary, T. W. Claydon, K. M. Dibb, and M. R. Boyett Base of Pore Loop Is Important for Rectification, Activation, Permeation, and Block of Kir3.1/Kir3.4 Biophys. J., June 1, 2006; 90(11): 4018 - 4034. [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]
|
|
|
|
|
|
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. M. Y Makary, T. W Claydon, D. Enkvetchakul, C. G Nichols, and M. R Boyett A difference in inward rectification and polyamine block and permeation between the Kir2.1 and Kir3.1/Kir3.4 K+ channels J. Physiol., November 1, 2005; 568(3): 749 - 766. [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]
|
|
|
|
|
|
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]
|
|
|
|
|
|
E. Zaks-Makhina, Y. Kim, E. Aizenman, and E. S. Levitan Novel Neuroprotective K+ Channel Inhibitor Identified by High-Throughput Screening in Yeast Mol. Pharmacol., January 1, 2004; 65(1): 214 - 219. [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]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
