The multi-ion nature of the pore in Shaker K+ channels.
We have investigated some of the permeation properties of the pore in Shaker K channels. We determined the apparent permeability ratio of K+, Rb+, and NH4+ ions and block of the pore by external Cs+ ions. Shaker channels were expressed with the baculovirus/Sf9 expression system and the channel currents measured with the whole-cell variant of the patch clamp technique. The apparent permeability ratio, PRb/PK, determined in biionic conditions with internal K+, was a function of external Rb+ concentration. A large change in PRb/PK occurred with reversed ionic conditions (internal Rb+ and external K+). These changes in apparent permeability were not due to differences in membrane potential. With internal K+, PNH4/PK was not a function of external NH4+ concentration (at least over the range 50-120 mM). We also investigated block of the pore by external Cs+ ions. At a concentration of 20 mM, Cs+ block had a voltage dependence equivalent to that of an ion with a valence of 0.91; this increased to 1.3 at 40 mM Cs+. We show that a 4-barrier, 3-site permeation model can simulate these and many of the other known properties of ion permeation in Shaker channels.
Pérez-Cornejo
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University of Rochester Medical School, Department of Physiology, New York 14642.
Begenisich
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D000641:Ammonia / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D016367:Baculoviridae; D002460:Cell Line; D002463:Cell Membrane Permeability; D002586:Cesium / Q000494:pharmacology; D004330:Drosophila; D004558:Electric Stimulation; D007700:Kinetics; D008433:Mathematics; D008564:Membrane Potentials / Q000187:drug effects; D008954:Models, Biological; D009036:Moths; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D015221:Potassium Channels / Q000096:biosynthesis / Q000502:physiology*; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D012413:Rubidium / Q000378:metabolism / Q000494:pharmacology
D015221:Potassium Channels; D011994:Recombinant Proteins; D002586:Cesium; D000641:Ammonia; D012413:Rubidium; D011188:Potassium