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. 1985 Sep;48(3):477–484. doi: 10.1016/S0006-3495(85)83803-0

The K+ channel of sarcoplasmic reticulum. A new look at Cs+ block.

S Cukierman, G Yellen, C Miller
PMCID: PMC1329361  PMID: 2412606

Abstract

K+-selective ion channels from mammalian sarcoplasmic reticulum were inserted into planar phospholipid bilayers, and single-channel currents measured in solutions containing Cs+. Current through this channel can be observed in symmetrical solutions containing only Cs+ salts. At zero voltage, the Cs+ conductance is approximately 15-fold lower than the corresponding K+ conductance. The open channel rectifies strongly in symmetrical Cs+ solutions, and the Cs+ currents are independent of Cs+ concentration in the range 18-600 mM. Biionic (Cs+/K+) reversal potentials are only 10 mV, showing that Cs+ is nearly as permeant as K+, though much less conductive. Addition of Cs+ to symmetrical K+ solutions reduces current through the channel in a voltage-dependent way. The results can be explained by a free energy profile in which the channel's selectivity filter acts in two ways: to provide binding sites for the conducting ions and to serve as a major rate-determining structure. According to this picture, the main difference between high-conductance K+ and low-conductance Cs+ is that Cs+ binds to an asymmetrically positioned site approximately 20-fold more tightly than does K+.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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