1. D. A view of ion permeation through the channel illustrates the changes in occupancy of the various K+ binding sites. A pair of ions hops in concert between a pair of binding sites in the selectivity filter. In the initial state, the "outer configuration," a pair of ions is bound to sites 1 and 3. As an ion enters the inner mouth of the channel, the ion in the inner chamber jumps to occupy the innermost binding site of the selectivity filter (site 4). This causes the pair of ions in the outer configuration to hop outward, expelling an ion from the channel. The two ions now in the inner configuration (sites 2 and 4) can hop to binding sites 1 and 3, returning the channel to its initial state (the outer configuration), from which it can conduct a second K+ ion. (Adapted, with permission, from Miller 2001.)
Source: Ion Channels, Principles of Neural Science, Fifth Editon
Citation: Kandel ER, Schwartz JH, Jessell TM, Siegelbaum SA, Hudspeth AJ, Mack S. Principles of Neural Science, Fifth Editon; 2012 Available at: Accessed: November 12, 2017
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