Permeation and gating of an inwardly rectifying potassium channel. Evidence for a variable energy well.
Permeation, gating, and their interrelationship in an inwardly rectifying potassium (K+) channel, ROMK2, were studied using heterologous expression in Xenopus oocytes. Patch-clamp recordings of single channels were obtained in the cell-attached mode. The gating kinetics of ROMK2 were well described by a model having one open and two closed states. One closed state was short lived (approximately 1 ms) and the other was longer lived (approximately 40 ms) and less frequent (approximately 1%). The long closed state was abolished by EDTA, suggesting that it was due to block by divalent cations. These closures exhibit a biphasic voltage dependence, implying that the divalent blockers can permeate the channel. The short closures had a similar biphasic voltage dependence, suggesting that they could be due to block by monovalent, permeating cations. The rate of entering the short closed state varied with the K+ concentration and was proportional to current amplitude, suggesting that permeating K+ ions may be related to the short closures. To explain the results, we propose a variable intrapore energy well model in which a shallow well may change into a deep one, resulting in a normally permeant K+ ion becoming a blocker of its own channel.
Choe
H
H
Department of Physiology and Biophysics, Cornell University Medical College, New York 10021, USA.
Sackin
H
H
Palmer
L G
LG
D000818:Animals; D001464:Barium / Q000494:pharmacology; D002586:Cesium / Q000494:pharmacology; D002614:Chelating Agents / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D004558:Electric Stimulation; D004734:Energy Metabolism / Q000502:physiology*; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D009865:Oocytes / Q000502:physiology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000502:physiology*; D024661:Potassium Channels, Inwardly Rectifying; D012413:Rubidium / Q000494:pharmacology; D014982:Xenopus laevis
D002614:Chelating Agents; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D002586:Cesium; D001464:Barium; D004492:Edetic Acid; D012413:Rubidium; D011188:Potassium