Conduction properties of the cloned Shaker K+ channel.
The conduction properties of the cloned Shaker K+ channel were studied using electrophysiological techniques. Single channel conductance increases in a sublinear manner with symmetric increases in K+ activity, reaching saturation by 0.6 M K+. The Shaker K+ channel is highly selective among monovalent cations; under bi-ionic conditions, its selectivity sequence is K+ > Rb+ > NH+4 > Cs+ > Na+, whereas, by relative conductance in symmetric solutions, it is K+ > NH+4 > Rb+ > Cs+. In Cs+ solutions, single channel currents were too small to be measured directly, so nonstationary fluctuation analysis was used to determine the unitary Cs+ conductance. The single channel conductance displays an anomalous molefraction effect in symmetric mixtures of K+ and NH+4, suggesting that the conducting pore is occupied by multiple ions simultaneously.
Heginbotham
L
L
Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115.
MacKinnon
R
R
D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D002414:Cations, Monovalent / Q000378:metabolism; D002586:Cesium / Q000378:metabolism; D003001:Cloning, Molecular; D004330:Drosophila / Q000235:genetics / Q000378:metabolism; D004553:Electric Conductivity; D004594:Electrophysiology; D005260:Female; D066298:In Vitro Techniques; D008564:Membrane Potentials; D009865:Oocytes / Q000378:metabolism; D010539:Permeability; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism*; D014981:Xenopus / Q000378:metabolism
D002414:Cations, Monovalent; D015221:Potassium Channels; D002586:Cesium