CHANNELS, RECEPTORS, AND ELECTRICAL SIGNALING |
ON THE ORIGIN OF ASYMMETRIC INTERACTIONS BETWEEN PERMEANT ANIONS AND THE CFTR CHLORIDE CHANNEL PORE
Mohammad Fatehi 1, Chantal N St. Aubin 1 and Paul Linsdell 1*
1 Dalhousie University
* To whom correspondence should be addressed. E-mail: paul.linsdell{at}dal.ca.
Submitted on August 15, 2006
Revised on September 11, 2006
Accepted on 7 November 2006
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Abstract |
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Single channel and macroscopic current recording was used to investigate block of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel pore by the permeant anion Au(CN)2-. Block was one to two orders of magnitude stronger when Au(CN)2- was added to the intracellular versus the extracellular solution, depending on membrane potential. A point mutation within the pore, T338A, strongly decreased the asymmetry of block, by weakening block by intracellular Au(CN)2- and at the same time strengthening block by external Au(CN)2-. Block of T338A, but not wild type, was strongest at the current reversal potential and weakened by either depolarization or hyperpolarization. In contrast to these effects, the T338A mutation had no impact on block by the impermeant Pt(NO2)42- ion. We suggest that the CFTR pore has at least two anion binding sites at which Au(CN)2- and Pt(NO2)42- block Cl- permeation. The T338A mutation decreases a barrier for Au(CN)2- movement between different sites, leading to significant changes in its blocking action. Our finding that apparent blocker binding affinity can be altered by mutagenesis of a residue which does not contribute to a blocker binding site have important implications for interpreting the effects of mutagenesis on channel blocker effects.
Key Words:
Anion permeation, Au(CN)2, Ion channel, Ionic selectivity, Lyotropic anions, Open channel block
