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J. Gen. Physiol., Volume 112, Number 4, October 1, 1998 433-446

Permeation and Gating of an Inwardly Rectifying Potassium Channel
Evidence for a Variable Energy Well

Han Choe,* Henry Sackin,Dagger and Lawrence G. Palmer*

From the * Department of Physiology and Biophysics, Cornell University Medical College, New York 10021; and Dagger  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


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