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© The Rockefeller University Press, 0022-1295/1998//433/ $5.00
Journal of General Physiology, Volume 112, Number 4, 1998

Article

Permeation and Gating of an Inwardly Rectifying Potassium Channel

Evidence for a Variable Energy Well



Han Choe*, Henry Sackin{ddagger}, and Lawrence G. Palmer*

From the * Department of Physiology and Biophysics, Cornell University Medical College, New York 10021; and {ddagger} Department of Physiology and Biophysics, The Chicago Medical School, North Chicago, Illinois 60064

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 (~1 ms) and the other was longer lived (~40 ms) and less frequent (~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.

Key Words: ROMK channel • barium • rubidium • cesium • oocyte

Address correspondence to Lawrence G. Palmer, Department of Physiology and Biophysics, Cornell University Medical College, 1300 York Avenue, New York, NY 10021. Fax: 212-746-8690; E-mail: lgpalm @mail.med.cornell.edu

Abbreviations: Kir channel, inwardly rectifying K+ channel


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