Ion Conduction through C-Type Inactivated Shaker Channels |
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Authors: | John G. Starkus Lioba Kuschel Martin D. Rayner Stefan H. Heinemann |
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Affiliation: | From the *Research Unit Molecular and Cellular Biophysics, Max Planck Society, D-07747 Jena, Germany; ‡Békésy Laboratory of Neurobiology, Pacific Biomedical Research Center, and §Department of Physiology, School of Medicine, University of Hawaii, Honolulu, Hawaii 96822-2359 |
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Abstract: | C-type inactivation of Shaker potassium channels involves entry into a state (or states) in which the inactivated channels appear nonconducting in physiological solutions. However, when Shaker channels, from which fast N-type inactivation has been removed by NH2-terminal deletions, are expressed in Xenopus oocytes and evaluated in inside-out patches, complete removal of K+ ions from the internal solution exposes conduction of Na+ and Li+ in C-type inactivated conformational states. The present paper uses this observation to investigate the properties of ion conduction through C-type inactivated channel states, and demonstrates that both activation and deactivation can occur in C-type states, although with slower than normal kinetics. Channels in the C-type states appear “inactivated” (i.e., nonconducting) in physiological solutions due to the summation of two separate effects: first, internal K+ ions prevent Na+ ions from permeating through the channel; second, C-type inactivation greatly reduces the permeability of K+ relative to the permeability of Na+, thus altering the ion selectivity of the channel. |
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Keywords: | potassium channels channel inactivation ion selectivity patch clamp Xenopus oocyte |
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