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Ionic permeation and blockade in Ca2+-activated K+ channels of bovine chromaffin cells

Single channel currents through Ca2+-activated K+ channels of bovine chromaffin cells were measured to determine the effects of small ions on permeation through the channel. The channel selects strongly for K+ over Na+ and Cs+, and Rb+ carries a smaller current through the channel than K+. Tetraethy...

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Detalles Bibliográficos
Formato: Texto
Lenguaje:English
Publicado: The Rockefeller University Press 1984
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2228735/
https://www.ncbi.nlm.nih.gov/pubmed/6092514
Descripción
Sumario:Single channel currents through Ca2+-activated K+ channels of bovine chromaffin cells were measured to determine the effects of small ions on permeation through the channel. The channel selects strongly for K+ over Na+ and Cs+, and Rb+ carries a smaller current through the channel than K+. Tetraethylammonium ion (TEA+) blocks channel currents when applied to either side of the membrane; it is effective at lower concentrations when applied externally. Millimolar concentrations of internal Na+ reduce the average current through the channel and produce large fluctuations (flicker) in the open channel currents. This flickery block is analyzed by a new method, amplitude distribution analysis, which can measure block and unblock rates in the microsecond time range even though individual blocking events are not time-resolved by the recording system. The analysis shows that the rate of block by Na+ is very voltage dependent, but the unblock rate is voltage independent. These results can be explained easily by supposing that current flow through the channel is diffusion limited, a hypothesis consistent with the large magnitude of the single channel current.