The ligand-sensitive gate of a potassium channel lies close to the selectivity filter.
Potassium channels selectively conduct K(+) ions across cell membranes and have key roles in cell excitability. Their opening and closing can be spontaneous or controlled by membrane voltage or ligand binding. We used Ba(2+) as a probe to determine the location of the ligand-sensitive gate in an inwardly rectifying K(+) channel (Kir6.2). To a K(+) channel, Ba(2+) and K(+) are of similar sizes, but Ba(2+) blocks the pore by binding within the selectivity filter. We found that internal Ba(2+) could still access its binding site when the channel was shut, which indicates that the ligand-sensitive gate lies above the Ba(2+)-block site, and thus within or above the selectivity filter. This is in marked contrast to the voltage-dependent gate of K(V) channels, which is located at the intracellular mouth of the pore.
Proks
Peter
P
University Laboratory of Physiology, Parks Road, Oxford OX1 3PT, UK.
Antcliff
Jennifer F
JF
Ashcroft
Frances M
FM
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D002413:Cations, Divalent; D008024:Ligands; D024661:Potassium Channels, Inwardly Rectifying; D011994:Recombinant Proteins; D002104:Cadmium; D001464:Barium; D012834:Silver; D000255:Adenosine Triphosphate; D011188:Potassium