Charges in the Cytoplasmic Pore Control Intrinsic Inward Rectification and Single-Channel Properties in Kir1.1 and Kir2.1 Channels
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An E224G mutation of the Kir2.1 channel generates intrinsic inward rectification and single-channel fluctuations in the absence of intracellular blockers. In this study, we showed that positively charged residues H226, R228 and R260, near site 224, regulated the intrinsic inward rectification and single-channel properties of the E224G mutant. By carrying out systematic mutations, we found that the charge effect on the intrinsic inward rectification and single-channel conductance is consistent with a long-range electrostatic mechanism. A Kir1.1 channel where the site equivalent to E224 in the Kir2.1 channel is a glycine residue does not show inward rectification or single-channel fluctuations. The G223K and N259R mutations of the Kir1.1 channel induced intrinsic inward rectification and reduced the single-channel conductance but did not generate large open-channel fluctuations. Substituting the cytoplasmic pore of the E224G mutant into the Kir1.1 channel induced open-channel fluctuations and intrinsic inward rectification. The single-channel conductance of the E224G mutant showed inward rectification. Also, a voltage-dependent gating mechanism decreased open probability during depolarization and contributed to the intrinsic inward rectification in the E224G mutant. In addition to an electrostatic effect, a close interaction of K+ with channel pore may be required for generating open-channel fluctuations in the E224G mutant.
KeywordsIntrinsic inward rectification Kir channel Electrostatic potential Single-channel conductance Open-channel fluctuation Chimera
We thank Drs. Lily Jan and James N. Weiss for kindly providing the Kir2.1 and Kir1.1 clones, respectively. We are grateful to Dr. Tom Barkas for reading and editing the manuscript. This work was supported by the Academia Sinica and by the National Science Council of Taiwan (grants 94–2320-B-001–025 and 95–2320-B001–011).
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