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Biophys. J. BioFAST: First Published March 2, 2006. doi:10.1529/biophysj.105.073569
© 2006 by the Biophysical Society.

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CHANNELS, RECEPTORS, AND ELECTRICAL SIGNALING

Base of Pore Loop is Important for Rectification, Activation, Permeation and Block of Kir3.1/Kir3.4

Samy Makary Youssef Makary 1, Tom W. Claydon 2, Katharine M. Dibb 1 and Mark R. Boyett 1*

1 University of Manchester
2 University of British Columbia

* To whom correspondence should be addressed. E-mail: mark.boyett{at}manchester.ac.uk.

Submitted on August 30, 2005
Revised on October 3, 2005
Accepted on 13 January 2006


  Abstract
The Kir3.1/Kir3.4 channel is an inward rectifier, agonist-activated K+ channel. The location of the binding site within the channel pore that coordinates polyamines (and is thus responsible for inward rectification) and the location of the gate that opens the channel in response to agonist-activation is unclear. In the present study, we show, not surprisingly, that mutation of residues at the base of the selectivity filter in the pore loop and second transmembrane domain weakens Cs+ block and decreases selectivity (as measured by Rb+ and spermine permeation). However, unexpectedly, the mutations also weaken inward rectification and abolish agonist-activation of the channel. In the wild-type channel and 34 mutant channels, there are significant (P<0.05) correlations among the KD for Cs+ block, Rb+ and spermine permeation, inward rectification and agonist-activation. The significance of these findings is discussed. One possible conclusion is that the selectivity filter is responsible for inward rectification and agonist-activation as well permeation and block.

Key Words: ACh-activated K+ channel, Agonist-activation, Inward rectification, Ion channels, Polyamines, Selectivity filter




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Copyright © 2006 by the Biophysical Society.